Journal of Applied Physiology Watch the video to learn how APS reaches out to developing nations.
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

J Appl Physiol 102: 628-633, 2007. First published November 2, 2006; doi:10.1152/japplphysiol.00449.2006 Free Article
8750-7587/07 $8.00
This Article
Free upon publication Free Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF) Free
Right arrow All Versions of this Article:
102/2/628    most recent
00449.2006v1
Right arrow Submit a response
Right arrow Alert me when this article is cited
Right arrow Alert me when eLetters are posted
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via ISI Web of Science (1)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Kolwicz, S. C.
Right arrow Articles by Libonati, J. R.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Kolwicz, S. C.
Right arrow Articles by Libonati, J. R.

Effects of forskolin on inotropic performance and phospholamban phosphorylation in exercise-trained hypertensive myocardium

Stephen C. Kolwicz,1 Hajime Kubo,2 Scott M. MacDonnell,3 Steven R. Houser,2,3 and Joseph R. Libonati1,2,3

1Department of Kinesiology, 2Cardiovascular Research Center, and 3Department of Physiology, Temple University, Philadelphia, Pennsylvania

Submitted 19 April 2006 ; accepted in final form 30 October 2006


   ABSTRACT
TOP
 ABSTRACT
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
beta-Adrenergic receptor (beta-AR) responsiveness is downregulated in left ventricular (LV) hypertrophy induced by chronic hypertension. While exercise training in hypertension enhances beta-AR responsiveness, the role of adenylyl cyclase remains unclear. The purpose of the present study was to test whether treadmill running in the spontaneously hypertensive rat (SHR) model improves LV responsiveness to forskolin (FOR) or the combination of FOR + isoproterenol (FOR+ISO). Female SHR (16-wk) were randomly placed into sedentary (SHR-SED; n = 7) or treadmill-trained (SHR-TRD; n = 8) groups. Wistar-Kyoto (WKY; n = 7) animals acted as normotensive controls. Langendorff, isovolumic LV performance was established at baseline and during incremental FOR infusion (1 and 5 µmol/l) and FOR+ISO (5 µmol/l + 1x10–8 mol/l). Heart rate, systolic blood pressure, and heart-to-body weight ratio were lower in WKY relative to both SHR groups (P < 0.05). LV performance and heart rate significantly increased in all groups to a similar extent with incremental FOR infusion. However, in the presence of 5 µmol/l FOR, ISO increased LV developed pressure, positive change in LV pressure, and negative change in LV pressure to a greater extent in SHR-TRD relative to SHR-SED (P < 0.05). Phospholamban phosphorylation at the Thr17 was greater in SHR-TRD relative to SHR-SED and WKY (P < 0.05). Absolute LV developed pressure was moderately correlated with phospholamban phosphorylation at both the Ser16 (r = 0.64; P < 0.05) and Thr17 (r = 0.52; P < 0.05). Our data suggest that the adenylyl cyclase step in the beta-AR cascade is not downregulated in the early course of hypertension and that the enhanced beta-AR responsiveness with training is likely mediated at levels other than adenylyl cyclase. Our data also suggest that beta-AR inotropic responsiveness in the presence of direct adenylyl cyclase agonism is improved in trained compared with sedentary SHR hearts.

heart; hypertrophy; diastole; proteins; spontaneously hypertensive rat

THE beta-ADRENERGIC RECEPTOR (beta-AR) system is an integral pathway in regulating myocardial inotropy and lusitropy, particularly during the stress of exercise (43, 46, 51). With hypertension, however, the beta-AR system is downregulated via receptor uncoupling (10, 27) and is clearly one hallmark of the maladaptive phenotype associated with compensatory hypertrophy (50). Recent data from our laboratory have shown that exercise training improves beta-AR responsiveness in the spontaneously hypertensive rat (SHR) model by mitigating the left ventricular (LV) abundance of the beta-AR receptor desensitizing kinase, G protein receptor kinase 2 (GRK2) (27). As a result of "restored" beta-AR signaling, PKA-mediated phosphorylation of key sarcoplasmic reticulum (SR) Ca2+ handling proteins, such as the ryanodine receptor and phospholamban (PLB), were improved with training (27). However, given that direct adenylyl cyclase/cAMP signaling may also be altered with hypertension (9, 28, 31), it remains unclear from our previous work whether "downstream-associated" beta-AR mechanisms are likewise improved by training.

Thus one purpose of the present study was to examine whether exercise training superimposed on hypertension would also elicit a putative physiological effect in response to direct adenylyl cyclase agonism via forskolin infusion. Forskolin is a diterpene derivative synthesized from the root of Coleus forskolii (4). Forskolin activates adenylate cyclase by binding to the cytosolic domain of the membrane-bound enzyme and leads to cAMP generation in a reversible manner, irrespective of cell surface receptors (44). This is of particular interest because, although both direct beta-AR agonism with isoproterenol and downstream signaling with forskolin result in a dose-dependent increase in intracellular cAMP, differences in cellular compartmentation of these systems allow for a more prolific rise in intracellular Ca2+ concentration ([Ca2+]i) and inotropy with isoproterenol (18, 23, 25, 45, 48). Moreover, since PKA can phosphorylate and uncouple beta-AR signaling, we also examined whether concurrent forskolin and isoproterenol infusion would induce a differential inotropic response in the hypertensive sedentary and trained myocardium. We hypothesized that beta-AR responsiveness would be enhanced with exercise training in the presence of elevated forskolin-induced increases in cAMP.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
Animal care and exercise training.   Twenty-two 16-wk-old female Wistar Kyoto (WKY, n = 7) and SHR (n = 15) (weighing ~200 g) were obtained from Charles River Laboratories (St. Constant, Quebec, Canada). Animals within the SHR group were randomly assigned into either a sedentary (SHR-SED) (N = 7) or an exercise-trained (SHR-TRD) (N = 8) group. All rats were housed three to five per cage. Animals were maintained on a 12:12-h light-dark cycle and fed ad libitum (Harlan Teklad Global Diets, 18% protein diet, Madison, WI). Exercise training consisted of low-intensity endurance training at a speed of 22 m/min, 0% grade, 60 continuous minutes, 5 days/wk, for a period of 12 wk. Resting heart rates (HRs) (mean of 25 cardiac cycles) and blood pressures were collected before death, utilizing a tail cuff apparatus (Kent Scientific, Torrington, CT). At 28 wk of age, animals were killed, and functional studies were performed. All animals received humane care in compliance with Temple University Institutional Animal Care and Use Committee Standards and the "Principles of Laboratory Animal Care" formulated by the National Society for Medical Research and the "Guide for the Care and Use of Laboratory Animals" prepared by the Institute of Laboratory Animal Resources and published by the National Institutes of Health (NIH Publication no. 85–23, revised 1985).

Langendorff isovolumic preparation.   Rats were anesthetized with pentobarbital sodium (60 mg/kg ip) and heparinized intravenously (500 units iv). The heart was excised, trimmed of excess tissue, and rapidly immersed in cold (4°C) Ca2+-free Krebs-Henseleit buffer. As previously described (27, 40, 41), hearts were placed on a Langendorff perfusion apparatus (ML785B2, ADInstruments, Colorado Springs, CO) and perfused at 16 ml/min (STH pump controller ML175, ADInstruments, Colorado Springs, CO) with a modified Krebs-Henseleit solution containing (in mM) 2.0 Ca2+ Cl2, 130 NaCl, 5.4 KCl, 11 dextrose, 2 pyruvate, 0.5 MgCl2, 0.5 NaH2PO4, and 25 NaHCO3, and aerated with 95% oxygen and 5% carbon dioxide, pH 7.35–7.4. A drainage cannula was inserted into the apex of the LV cavity through a left atrial incision. A balloon was inserted into the LV cavity, and the balloon volume was adjusted to yield 9–10 mmHg of LV end-diastolic pressure (LVEDP), and no further alterations in balloon volume were made. All hearts were immersed in a water-jacketed organ chamber to maintain a constant temperature of 37°C and allowed to equilibrate for 20 min.

LV pressure, LVEDP, the maximum rate of positive and negative change in LV pressure (±dP/dt), and coronary flow rate were continuously recorded by a data-acquisition system (Powerlab/8SP, ADI Instruments, Colorado Springs, CO). LV developed pressure (LVDP) was calculated by subtracting the LVEDP from the LV systolic pressure. The mean of five cardiac cycles was used to quantify LV performance.

Experimental paradigm.   Following equilibration, preagonist baseline data were recorded. Following baseline, isolated hearts underwent incremental forskolin infusion at 5-min intervals at the following concentrations: 1 and 5 µmol/l. The peak LV response was analyzed at both concentrations. Isoproterenol infusion (1x10–8 mol/l) was then superimposed on 5 µmol/l forskolin to examine whether direct adenylyl cyclase activation would lead to beta-AR uncoupling.

Western blot analysis.   Following the isolated heart experiments, an apical section of the LV was frozen in liquid nitrogen. Frozen tissue was weighed and homogenized on ice in a PBS lysis buffer containing 2% SDS, 1% Igepal CA-630, 0.5% deoxycholate, 5 mM EDTA (pH 7.4), and proteinase inhibitors [10 µg/ml aprotinin, 10 µg/ml leupeptin, 1 mM 4-(2-aminoethyl) benzenesulfonyl fluoride hydrochloride, 5 µg/ml pepstatin A, and 200 µg/ml benzamidine]. The supernatant was assayed for total protein concentration, mixed with equal volume of SDS sample buffer [2% SDS, 0.1 M Tris·HCl (pH 6.8), 20% glycerol, 100 mM dithiothreitol, and 0.02% bromphenol blue], and stored at –80°C.

Tissue protein abundance and phosphorylation levels in isolated protein were analyzed using Western blot analysis, as described previously (27). Target antigens were probed with the nonphosphorylation-specific monoclonal antibodies: PLB total (Upstate Biotechnology, Waltham, MA) and sarcomeric actin (Sigma, St. Louis, MO). Phosphorylation-specific polyclonal antibodies Ser16-PLB (Ser16) and Thr17-PLB (Thr17) (gift from Dr. J Colyer, University of Leeds, UK) also were probed.

Films were scanned (UMAX PowerLook 1100), and band intensities were quantified with densitometric analysis using the Scion Image program (version 1.62). To normalize blot-to-blot difference in protein loading or transfer efficiency, a common sample was included. Target bands were normalized to actin measured in the same sample. All of the PLB phosphorylation data reported in this paper are following joint agonism with both forskolin and isoproterenol stimulation.

Soleus citrate synthase activity.   Immediately following death, the right soleus from a subset of animals was dissected from each hindlimb, frozen in liquid nitrogen, and stored at –80°C until analysis. In brief, samples were homogenized on ice in a cell lysis reagent (Sigma) and centrifuged at 4°C for 15 min at 12,000 rpm. The supernatant was collected, and a standardized concentration of protein was assayed for citrate synthase activity using a commercial reagent kit (Sigma) by methods previously described by Srere (47).

Data analysis and interpretation.   In vivo hemodynamics, animal characteristics, Western blots, and citrate synthase activity were compared with one-way analysis of variance followed by a least significant difference post hoc analysis. The LV response to forskolin was compared with ANOVA for repeated measures followed by one-way analysis of variance and Fisher's least significant difference post hoc comparisons at each forskolin concentration. Pearson product correlations were performed between LVDP and phosphamban phosphorylation. All analyses were performed on SPSS (SPSS, Chicago, IL, release 13.0). Significance was set at an {alpha}-level of P < 0.05. All data are reported as the means ± SE.


   RESULTS
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 GRANTS
 REFERENCES
 
In vivo hemodynamics and physical characteristics.   Resting HR and systolic blood pressure (SBP) immediately before the time of death are presented in Table 1. HR and SBP were significantly lower in WKY vs. both SHR groups (P < 0.01), while SBP was unaffected by training. The physical characteristics of the animals are also presented in Table 1. Before death, body weight was significantly lower in SHR-SED relative to SHR-TRD. Absolute heart weight (HW) was greater in SHR-TRD relative to WKY (P < 0.05). HW-to-body weight ratio was significantly lower in WKY vs. both SHR groups (P < 0.01). Absolute tibial length and HW-to-tibial length ratio were similar between groups. Table 2 shows that soleus citrate synthase activity was increased in SHR-TRD relative to both WKY and SHR-SED (P < 0.01).


View this table:
[in this window]
[in a new window]

  		Table 1. In vivo hemodynamics and physical characteristics

 

View this table:
[in this window]
[in a new window]

  		Table 2. Citrate synthase activity

 
Langendorff LV performance.   Table 3 shows that the LV baseline performance was similar between groups when the LVEDP was experimentally fixed at 9–10 mmHg. Coronary perfusion pressure was greater in SHR-SED relative to WKY (P < 0.05), and SHR-TRD was similar to WKY. Figure 1 illustrates the LV responsiveness to incremental forskolin infusion and forskolin + isoproterenol. LVDP, +dP/dt, –dP/dt, and HR increased similarly from baseline in all groups with incremental forskolin infusion (Fig. 1, A, C, D, and E). In the presence of 5 µmol/l forskolin, isoproterenol increased LVDP, +dP/dt, and –dP/dt to a significantly greater extent in SHR-TRD relative to SHR-SED. Incremental forskolin infusion did not impact coronary perfusion pressure differently between groups (Table 4), with the caveat that differences in baseline coronary perfusion pressure between WKY and SHR persisted throughout the protocol.


View this table:
[in this window]
[in a new window]

  		Table 3. Baseline Langendorff LV performance

 

Figure 1
View larger version (13K):
[in this window]
[in a new window]

  		Fig. 1. Left ventricular (LV) Langendorff performance was established in response to incremental drug infusion [1 µM forskolin (For), 5 µM forskolin, and 5 µM forskolin + 1x10–8 M isoproterenol (Iso)]. A: LV developed pressure (LV Dev P); B: LV end-diastolic pressure (LVEDP); C: positive change in LV pressure (+dP/dt); D: negative change in LV pressure (–dP/dt); E: heart rate. Administration of forskolin increased LV inotropic performance beyond baseline values in all groups. With 5 µM forskolin + 1x10–8 M isoproterenol, LV developed pressure, +dP/dt, and –dP/dt were greater in trained spontaneously hypertensive rats (SHR-TRD) compared with sedentary spontaneously hypertensive rats (SHR-SED) (P < 0.05). bpm, Beats/min. Values are presented as means ± SE. {blacklozenge}, Wistar Kyoto (WKY; n = 7); {blacksquare}, SHR-SED (n = 7); {triangleup}, SHR-TRD (n = 8). *P < 0.05 vs. SHR-SED. {dagger}P < 0.05 vs. baseline. {ddagger}P < 0.05 vs. 1 µM forskolin.

 

View this table:
[in this window]
[in a new window]

  		Table 4. Coronary perfusion pressure

 
Western blot analysis.   Figure 2 illustrates total PLB abundance normalized to actin (A) and PLB phosphorylation at the Ser16 (B) and Thr17 (C) residues. Although PLB phosphorylation at Ser16 was similar between groups, PLB phosphorylation at Thr17 was significantly greater in SHR-TRD relative to SHR-SED and WKY. Furthermore, absolute LVDP was moderately correlated with PLB phosphorylation at both the Ser16 (r = 0.64; P < 0.05) and Thr17 (r = 0.52; P < 0.05) residues (see Fig. 3).


Figure 2
View larger version (27K):
[in this window]
[in a new window]

  		Fig. 2. Western blot analysis for total phospholamban (PLBt) abundance relative to actin (A) and phosphorylated PLB [Ser16 (B) and Thr17 (C)] relative to PLBt. Phosphorylated PLB at the Thr17 residues was significantly greater in SHR-TRD compared with WKY and SHR-SED (C), despite similar Ser16 phosphorylation between groups. MW, molecular weight. Solid bars, WKY; open bars, SHR-SED; hatched bars, SHR-TRD. Values are presented as means ± SE. *P < 0.05 SHR-TRD vs. WKY; {dagger}P < 0.05 SHR-TRD vs. SHR-SED.

 

Figure 3
View larger version (10K):
[in this window]
[in a new window]

  		Fig. 3. Correlation analysis between LV developed pressure and phosphorylated PLB [Ser16 (A) and Thr17 (B)] relative to PLBt abundance. LV developed pressure was moderately correlated with PLB phosphorylation at both the Ser16 (r = 0.64; P < 0.05) and Thr17 (r = 0.52; P < 0.05) residues.

 

   DISCUSSION
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
GRANTS
 REFERENCES
 
The major findings of this study are that, in myocardium harvested from the female SHR model: 1) the adenylyl cyclase step in the beta-AR cascade is not downregulated in the early course of hypertension; 2) exercise training-induced improvements in beta-AR responsiveness are not adenylyl cyclase dependent; and 3) in the presence of direct adenylyl cyclase agonism, beta-AR inotropic responsiveness is improved in SHR-TRD relative to SHR-SED hearts.

Our laboratory recently reported that exercise training improved beta-AR receptor responsiveness in the SHR model by attenuating myocardial levels of the beta-AR desensitizing kinase GRK2 (27). Improved beta-AR signaling with exercise training provided one mechanism for increased PKA-mediated phosphorylation of key SR Ca2+ handling proteins, such as the ryanodine receptor and PLB (Ser16 and Thr17). However, given that several studies have shown that G protein to adenylyl cyclase signaling is impaired in hypertension (1, 2, 5, 9, 14, 26, 28, 31, 32), we further examined whether improved beta-AR signaling with exercise training in hypertension was also, in part, mediated at the level of adenylyl cyclase. To our knowledge, the present study is the first to explore this topic.

In the present study, LV inotropic and lusitropic function was increased to a similar extent between groups with infusion of low doses of forskolin (1 and 5 µmol/l), suggesting that the adenylyl cyclase step in the beta-AR cascade is not downregulated in early compensated hypertrophy. These data are consistent with the paradigm that the training-induced improvement in beta-AR responsiveness in hypertension occurs at steps preceding the generation of cAMP and are consistent with previous studies that reported no differences in forskolin-stimulated inotropic responsiveness between SHR and WKY (2, 3).

Increased [Ca2+]i with beta-AR agonism activates Ca2+ calmodulin kinase, which, in turn, phosphorylates PLB, resulting in enhanced SR Ca2+ loading and subsequent increases in LV inotropic performance. LV inotropic performance is also regulated via PKA activation and subsequent PLB phosphorylation at the Ser16 residue. Our previous study showed that both Ser16 and Thr17 phosphorylation were attenuated in isoproterenol-treated SHR-SED hearts relative to WKY and SHR-TRD hearts (27). In the present study, however, PLB phosphorylation at both the Ser16 and Thr17 residues was normalized in SHR-SED after the infusion of concomitant forskolin and isoproterenol. These data reiterate the significance of steps preceding the generation of cAMP in dictating beta-AR downregulation in hypertension.

Protein kinase A exerts negative feedback control on the beta-AR by phosphorylating and uncoupling the receptor (21, 24). One aim of the present study was to determine whether adenylyl cyclase agonism with forskolin can exhibit inhibition on beta-AR differently in hypertensive sedentary and trained myocardium. These studies were performed on the basis that the beta-AR can, in seconds, become acutely desensitized via phosphorylation of its serine residue on the carboxy terminus, either by the GRK2 or by PKA directly. In the phosphorylated state, beta-arrestin can then induce internalization of the beta-AR. Our data show that beta-AR inotropic responsiveness with forskolin + isoproterenol was improved in trained vs. sedentary hypertensive hearts. Furthermore, Ca2+ calmodulin kinase-mediated PLB phosphorylation at the Thr17 residue was augmented with training. Training-induced alterations in beta-AR phosphorylation status and/or a reduction GRK2 abundance (27) are likely mechanistic candidates in explaining the enhanced inotropic responsiveness to forskolin and isoproterenol in exercise-trained hearts. However, differences in the cellular compartmentation of the cAMP system are also an important consideration. Although both isoproterenol and forskolin are known to increase LV inotropic and lusitropic function via increasing cAMP (8, 18, 22), it is hypothesized that cellular compartmentation allows for a more profuse increase in [Ca2+]i and contractility with isoproterenol (18, 23, 48). Patch-clamp experiments in LV cardiomyocytes show L-type Ca2+ current is more localized to the beta-AR with isoproterenol, whereas L-type Ca2+ current is more widely dispersed throughout the entire sarcolemma with forskolin (25). Thus, although speculative, another potential mechanism is that training may alter cellular compartmentation of the beta-AR system, such that the trained myocardium elicits a more localized and prolific response to beta-AR agonism compared with SHR-SED hearts.

Early studies show that one bout of acute exercise increases cAMP levels (19, 35, 36), an effect that is dependent upon the intensity and duration of exercise (20). However, data in chronic exercise training models are less clear. Exercise training studies in nonpathological models have elicited variable results with respect to myocardial beta-AR responsiveness, with some studies showing increased (29, 49, 52), decreased (11, 17), or no change (34, 37) with training. The unpredictable adaptive pattern of the beta-AR with training in normotensive myocardium is likewise reflected in variable observations reported in the plasticity of the adenylyl cyclase step in the cascade. In the basal state, adenylyl cyclase has been shown to be increased (6), decreased (16, 33), or unaltered (12, 30, 42) with training. Likewise, agonist stimulated adenylyl cyclase has also been reported to be increased (30, 39, 52), decreased (12, 30), or unaltered with training (6, 12, 42). Thus, in normotensive rodent myocardium, it is difficult to generate any categorical conclusions with respect to how exercise training impacts beta-AR responsiveness and adenylyl cyclase activity. Furthermore, there is a paucity of data with respect to how training impacts forskolin-stimulated adenylyl cyclase activity in compensatory hypertrophy, illustrating the novelty of the present study.

The SHR model was selected for our study because it mimics the slowly progressing clinical course of untreated essential hypertension in humans. It has been documented that concentric hypertrophy occurs in SHR between 6 and 12 mo of age, decompensating to heart failure near 15 mo (15, 38). We chose to study these animals at 7 mo of age because cardiac function is well maintained and fibrosis is minimal (7). There are several design considerations that may affect the interpretability of the present study. First, inclusion of a normotensive exercise group would have expanded our understanding of the exercise-induced adaptation. However, this was not the direct purpose of the present study, as we instead focused our efforts toward establishing the phenotype of the hypertensive myocardium in response to training. Second, although we utilized forskolin-stimulated Langendorff LV performance as an adenylyl cyclase activity surrogate, we did not directly measure adenylyl cyclase activity, phosphodiesterase activity, or G protein isoforms. Third, we did not uncouple the influence of Gs on adenylate cyclase such that the binding affinity for forskolin is relatively high in the presence of Gs{alpha} (EC50 = 0.1 µmol/l) and relatively low in the absence of Gs{alpha} (EC50 ~15 µmol/l) (13). Fourth, we only assessed PLB phosphorylation following agonism with forskolin and isoproterenol, thus not allowing for interpretation of basal differences.

In summary, our data suggest that the adenylyl cyclase step in the beta-AR cascade is not downregulated in the early course of hypertension and that the enhanced beta-AR responsiveness with training previously established in hypertension (27) is likely mediated at levels other than adenylyl cyclase. Our data also suggest that exercise training in hypertension shifts PKA-mediated phosphorylation and desensitization of the beta-AR rightward. The clinical significance of this paper is that, during acute stress and exercise, beta-AR responsiveness is more likely to be maintained in patients with hypertension-induced LV hypertrophy who are exercise trained.


   GRANTS
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 GRANTS
REFERENCES
 
This study was supported by a beginning-grant-in-aide from the American Heart Association, Mid-Atlantic Affiliate (J. R. Libonati), and National Heart, Lung, and Blood Institute Grant HL-33921 (S. R. Houser).


   FOOTNOTES
 

Address for reprint requests and other correspondence: J. R. Libonati, Temple Univ., 122 Pearson Hall, 1800 North Broad St., Philadelphia, PA 19122 (e-mail: jlibonat{at}temple.edu)

The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.


   REFERENCES
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 

  1. Anand-Srivastava MB. G-proteins and adenylyl cyclase signaling in hypertension. Mol Cell Biochem 157: 163–170, 1996.[Web of Science][Medline]
  2. Atkins FL, Bing O, Dimauro PG, Conrad CH, Robinson KG, Brooks WW. Modulation of left and right ventricular beta-adrenergic receptors from spontaneously hypertensive rats with left ventricular hypertrophy and failure. Hypertension 26: 78–82, 1995.[Abstract/Free Full Text]
  3. Beenan OH, Batink HD, Pfaffendorf M, van Zwieten PA. Beta-adrenoceptors in the hearts of diabetic-hypertensive rats: radioligand binding and functional experiments. Blood Press 6: 44–51, 1997.[Medline]
  4. Bhat SV, Bajwa BS, Dornauer H, De Souza NJ, Fehlhaber HW. Structures and stereochemistry of new Labdane diterpenoids from coleus forskolii. Tetrahedron Lett 19: 1669–1672, 1997.[CrossRef]
  5. Bohm M, Gierschik P, Knorr A, Larisch K, Weismann K, Erdmann E. Desensitization of adenylate cyclase and increase of Gi{alpha} in cardiac hypertrophy due to acquired hypertension. Hypertension 20: 103–112, 1992.[Abstract/Free Full Text]
  6. Bohm M, Dorner H, Htun P, Lensche H, Platt D, Erdmann E. Effects of exercise on myocardial adenylate cyclase and Gi{alpha} expression in senescence. Am J Physiol Heart Circ Physiol 264: H805–H814, 1993.[Abstract/Free Full Text]
  7. Boluyt MO, O'Neill L, Meredith AL, Bing OHL, Brooks WW, Conrad CH, Crow MT, Lakatta EG. Alterations in cardiac gene expression during the transition from stable hypertrophy to heart failure: marked upregulation of genes encoding extracellular matrix components. Circ Res 75: 23–32, 1994.[Abstract/Free Full Text]
  8. Buschmans E, Hearse DJ, Manning AS. Forskolin: effects on cyclic AMP and contractile function in the isolated rat and guinea pig heart. Can J Cardiol 1: 385–394, 1985.[Medline]
  9. Chen LC, Vatner DE, Vatner SF, Hittinger L, Homcy CJ. Decreased Gs{alpha} mRNA levels accompany the fall in Gs adenylyl cyclase activities in compensated left ventricular hypertrophy. J Clin Invest 87: 293–298, 1991.[Web of Science][Medline]
  10. Choi DJ, Koch WJ, Hunter JJ, Rockman HA. Mechanism of beta-adrenergic receptor desensitization in cardiac hypertrophy is increased beta-adrenergic receptor kinase. J Biol Chem 272: 17223–17229, 1997.[Abstract/Free Full Text]
  11. Crews J, Aldinger EE. Effect of chronic exercise on myocardial function. Am Heart J 74: 536–542, 1967.[CrossRef][Web of Science][Medline]
  12. Davidson WR, Banerjee SP, Liang CS. Dobutamine-induced cardiac adaptations: comparison with exercise-trained and sedentary rats. Am J Physiol Heart Circ Physiol 250: H725–H730, 1986.[Abstract/Free Full Text]
  13. Dessauer CW, Scully TT, Gilman AG. Interactions of forskolin and ATP with the cytosolic domains of mammalian adenylyl cyclase. J Biol Chem 272: 22272–22277, 1997.[Abstract/Free Full Text]
  14. DiFusco F, Hashim S, and Anand-Srivastava MB. Volume overload cardiac hypertrophy exhibits decreased expression of Gs{alpha} and not of Gi{alpha} heart. Am J Physiol Cell Physiol 279: C990–C998, 2000.[Abstract/Free Full Text]
  15. Doggrel SA, Brown L. Rat models of hypertension, cardiac hypertrophy and failure. Cardiovasc Res 39: 89–105, 1998.[Free Full Text]
  16. Dohm GL, Pennington SN, Barakat H. Effect of exercise training on adenylyl cyclase and phosphodiesterase in skeletal muscle, heart, and liver. Biochem Med 16: 138–142, 1976.[CrossRef][Web of Science][Medline]
  17. Ekblom B, Kilbom A, Soltysiak J. Sympathectomy and pharmacological blockade in trained rats. Acta Physiol Scand 89: 283–285, 1973.[Web of Science][Medline]
  18. England PJ, Shahid M. Effects of forskolin on contractile responses and protein phosphorylation in the isolated perfused rat heart. Biochem J 246: 687–695, 1987.[Web of Science][Medline]
  19. Goldfarb AH, Kendrick ZV. Effect of an exercise run to exhaustion on cAMP in the rat heart. J Appl Physiol 51: 1539–1542, 1981.[Abstract/Free Full Text]
  20. Goldfarb AH, Bruno JF, Buckenmeyer PJ. Intensity and duration effects of exercise on heart cAMP, phosphorylase, and glycogen. J Appl Physiol 60: 1268–1273, 1986.[Abstract/Free Full Text]
  21. Hausdorff WP, Caron MG, Lefkowitz RJ. Turning off the signal: densensitization of beta-adrenergic function. FASEB J 4: 2881–2890, 1990.[Abstract]
  22. Hearse DJ, Zucchi R, Buschmans E, Manning AS. Forskolin and myocardial function in the normal, ischemic and reperfused rat heart. Can J Cardiol 2: 303–312, 1986.[Medline]
  23. Hohl CM, Li QA. Compartmentation of cAMP in adult canine ventricular myocytes: relation to single-cell free Ca2+ transients. Circ Res 69: 1369–1379, 1991.[Abstract/Free Full Text]
  24. Iwami G, Kawabe J, Ebina T, Cannon PJ, Homcy CJ, Ishikawa Y. Regulation of adenylyl cyclase by protein kinase A. J Biol Chem 270: 12481–12484, 1995.[Abstract/Free Full Text]
  25. Jurevicius J, Fischmeister R. cAMP compartmentation is responsible for a local activation of cardiac Ca2+ channels by beta-adrenergic agonists. Proc Natl Acad Sci USA 93: 295–299, 1996.[Abstract/Free Full Text]
  26. Kumano K, Upsher ME, Khairallah PA. Beta-adrenergic receptor response coupling in hypertrophied hearts. Hypertension 5: I175–I183, 1983.[Web of Science][Medline]
  27. MacDonnell SM, Kubo H, Crabbe DL, Renna BF, Reger PO, Mohara J, Smithwick LA, Koch WJ, Houser SR, Libonati JR. Improved myocardial beta adrenergic responsiveness and signaling with exercise training in hypertension. Circulation 111: 3420–3428, 2005.
  28. McLellan AR, Milligan G, Houslay MD, Connell JM. G-proteins in experimental hypertension: a study of spontaneously hypertensive rat myocardial and renal cortical plasma membranes. J Hypertens 11: 365–372, 1993.[CrossRef][Web of Science][Medline]
  29. Mole PA. Increased contractile potential of papillary muscles from exercise-trained rat hearts. Am J Physiol Heart Circ Physiol 234: H421–H425, 1978.[Abstract/Free Full Text]
  30. Moore RL, Riedy M, Gollnick PD. Effect of training on beta-adrenergic receptor number in rat heart. J Appl Physiol 52: 1133–1137, 1982.[Abstract/Free Full Text]
  31. Morano I, Adler K, Weismann K, Knorr A, Erdmann E, Bohm M. Correlation of myosin heavy chain expression in the rat with cAMP in different models of hypertension-induced cardiac hypertrophy. J Mol Cell Cardiol 25: 387–394, 1993.[CrossRef][Web of Science][Medline]
  32. Nieto JL, Diaz-Laviada I, Guillen A, Garcia-Barreno P, Haro A. Cardiac beta-adrenoceptors, G-proteins and adenylate cyclase regulation during myocardial hypertrophy. Cell Signal 5: 169–179, 1993.[CrossRef][Web of Science][Medline]
  33. Nieto JL, Laviada ID, Guillen A, Haro A. Adenylyl cyclase system is affected differently by endurance physical training in heart and adipose tissue. Biochem Pharmacol 51: 1321–1329, 1996.[CrossRef][Web of Science][Medline]
  34. Nutter DO, Priest RE, Fuller EO. Endurance training in the rat. I. Myocardial mechanics and biochemistry. J Appl Physiol 51: 934–940, 1981.[Abstract/Free Full Text]
  35. Palmer WK, Studney TA, Doukas S. Exercise-induced increases in myocardial adenosine 3',5'-cyclic monophosphate and phosphodiesterase activity. Biochim Biophys Acta 672: 114–122, 1981.[Medline]
  36. Palmer WK. Effect of exercise on cardiac cyclic AMP. Med Sci Sports Exerc 20: 525–530, 1988.
  37. Paynter DE, Tipton CM, Tcheng T. Response of immunosympathectomized rats in training. J Appl Physiol 42: 935–940, 1977.[Abstract/Free Full Text]
  38. Pinto YM, Paul M, Ganten D. Lessons from rat models of hypertension: from Goldblatt to genetic engineering. Cardiovasc Res 39: 77–88, 1998.[Abstract/Free Full Text]
  39. Plourde G, Rousseau-Migneron S, Nadeau A. beta-Adrenergic adenylate cyclase system adaptation to physical training in rat ventricular tissue. J Appl Physiol 70: 1633–1638, 1991.[Abstract/Free Full Text]
  40. Reger PO, Barbe MF, Amin M, Renna BF, Hewston LA, MacDonnell SM, Houser SR, Libonati JR. Myocardial hypoperfusion/reperfusion tolerance with exercise training in hypertension. J Appl Physiol 100: 541–547, 2006.[Abstract/Free Full Text]
  41. Renna BF, Kubo H, MacDonnell SM, Crabbe DL, Reger PO, Houser SR, Libonati JR. Improved tolerance to acidosis with exercise in pressure-overload hypertrophy. Med Sci Sports Exerc 38: 847–855, 2006.
  42. Roth DA, White CD, Podolin DA, Mazzeo RS. Alterations in myocardial signal transduction due to aging and chronic dynamic exercise. J Appl Physiol 84: 177–184, 1998.[Abstract/Free Full Text]
  43. Scarpace PJ, Shu Y, Tumer N. Influence of exercise training on myocardial beta-adrenergic signal transduction: differential regulation with age. J Appl Physiol 77: 737–741, 1994.[Abstract/Free Full Text]
  44. Seamon KB, Padgett W, Daly JW. Forskolin: unique diterpene activator of adenylate cyclase in membranes and in intact cells. Proc Natl Acad Sci USA 78: 3363–3367, 1981.[Abstract/Free Full Text]
  45. Spah F. Forskolin, a new positive inotropic agent and its influence on myocardial electrogenic cation movements. J Cardiovasc Pharmacol 6: 99–106, 1984.[Medline]
  46. Spina RJ, Ogawa T, Coggan AR, Holloszy JO, Ehsani AA. Exercise training improves left ventricular contractile response to beta-adrenergic agonist. J Appl Physiol 72: 307–311, 1992.[Abstract/Free Full Text]
  47. Srere PA. Citrate synthase. Methods Enzymol 13: 3–11, 1969.[CrossRef]
  48. Steinberg SF, Brunton LL. Compartmentation of G protein-coupled signaling pathways in cardiac myocytes. Annu Rev Pharmacol Toxicol 41: 751–773, 2001.
  49. Takeda N, Dominiak D, Turek D, Rupp H, Jacob R. The influence of endurance training on mechanical catecholamine responsiveness, beta-adrenoceptor density and myosin isozyme pattern of rat ventricular myocardium. Basic Res Cardiol 80: 88–99, 1985.[CrossRef][Web of Science][Medline]
  50. Vatner DE, Asai K, Iwase M, Ishikawa Y, Shannon RP, Homcy CH, Vatner SF. Beta-adrenergic receptor-G protein-adenylyl cyclase signal transduction in the failing heart. Am J Cardiol 83: 80H–85H, 1999.[CrossRef][Web of Science][Medline]
  51. Vatner SF, Vatner DE, Homcy CJ. Beta-adrenergic receptor signaling: an acute compensatory adjustment-inappropriate for the chronic stress of heart failure? Insights from Gs alpha overexpression and other genetically engineered animal models. Circ Res 86: 502–506, 2000.[Free Full Text]
  52. Wyatt HL, Chuck L, Rabinowitz B, Tyberg JV, Parmley WW. Enhanced cardiac response to catecholamines in physically trained cats. Am J Physiol Heart Circ Physiol 234: H608–H613, 1978.[Free Full Text]



This article has been cited by other articles:


Home page
 Am. J. Physiol. Heart Circ. Physiol.Home page
S. M. MacDonnell, H. Kubo, D. M. Harris, X. Chen, R. Berretta, M. F. Barbe, S. Kolwicz, P. O. Reger, A. Eckhart, B. F. Renna, et al.
Calcineurin inhibition normalizes beta-adrenergic responsiveness in the spontaneously hypertensive rat
Am J Physiol Heart Circ Physiol, November 1, 2007; 293(5): H3122 - H3129.
[Abstract] [Full Text] [PDF]

This Article
Free upon publication Free Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF) Free
Right arrow All Versions of this Article:
102/2/628    most recent
00449.2006v1
Right arrow Submit a response
Right arrow Alert me when this article is cited
Right arrow Alert me when eLetters are posted
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via ISI Web of Science (1)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Kolwicz, S. C.
Right arrow Articles by Libonati, J. R.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Kolwicz, S. C.
Right arrow Articles by Libonati, J. R.

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
Visit Other APS Journals Online
Copyright © 2007 by the American Physiological Society.