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Departments of 1Biomedical Sciences and 2Medical Pharmacology and Physiology and 3Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri 65211; and 4Department of Kinesiology and Noll Physiological Research Center, The Pennsylvania State University, University Park, Pennsylvania 16802
Submitted 3 October 2003 ; accepted in final form 8 December 2003
The intracellular mechanisms underlying enhanced myogenic contraction (MC) in coronary resistance arteries (CRAs) from exercise-trained (EX) pigs have not been established. The purpose of this study was to test the hypothesis that exercise-induced alterations in protein kinase C (PKC) signaling underlie enhanced MC. Furthermore, we sought to determine whether modulation of intracellular Ca2+ signaling by PKC underlies enhanced MC in EX animals. Male Yucatan miniature swine were treadmill trained (n = 7) at 
75% of maximal O2 uptake for 16 wk (6 miles/h, 60 min) or remained sedentary (SED, n = 6). Diameter measurements in response to intraluminal pressure (60, 75, and 90 cmH2O) or 60 mM KCl were determined in single, cannulated CRAs (100 µm ID) with and without the PKC inhibitor chelerythrine (CE, 1 µM). Confocal imaging of Ca2+ signaling [myogenic Ca2+ (Cam)] was also performed in CRAs of similar internal diameter after abluminal loading of the Ca2+ indicator dye fluo 4 (1 µM, 37°C, 30 min). We observed significantly greater MC in CRAs isolated from EX than from SED animals at 90 cmH2O, as well as greater reductions in MC after CE at all pressures studied. At intraluminal pressures of 75 and 90 cmH2O, CE produced greater decreases in Cam in CRAs from EX than from SED animals (64% vs. 25%, P < 0.05). Inhibition of KCl constriction and Cam by CE was also greater in EX animals (P < 0.05). Western blotting revealed significant increases in Ca2+-dependent PKC-
(50%) but not Ca2+-independent PKC-
levels in CRAs isolated from EX animals (P < 0.05). We also observed significant group differences in phosphorylated PKC- levels. Finally, voltage-gated Ca2+ current (VGCC) was effectively blocked by CE, bisindolylmaleimide, and staurosporine in isolated smooth muscle cells from CRAs, providing evidence for a mechanistic link between VGCCs and PKC in our experimental paradigm. These results suggest that enhanced MC in CRAs from EX animals involves PKC-dependent modulation of intracellular Ca2+, including regulation of VGCCs.
protein kinase C; voltage-gated calcium channels
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