Journal of Applied Physiology
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J Appl Physiol (December 12, 2003). doi:10.1152/japplphysiol.01077.2003
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Submitted on October 3, 2003
Accepted on December 8, 2003

Alterations in PKC signaling underlie enhanced myogenic tone in exercise-trained porcine coronary resistance arteries

D. H Korzick1, M. H Laughlin2, and D. K Bowles3*

1 Biomedical Sciences, University of Missouri, Columbia, Missouri, USA; Kinesiology, The Pennsylvania State University, University Park, Pennsylvania, USA; Noll Physiological Research Center, The Pennsylvania State University, University Park, Pennsylvania, USA
2 Biomedical Sciences, University of Missouri, Columbia, Missouri, USA; Medical Pharmacology and Physiology, University of Missouri, Columbia, Missouri, USA; Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri, USA
3 Biomedical Sciences, University of Missouri, Columbia, Missouri, USA; Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri, USA

* To whom correspondence should be addressed. E-mail: bowlesd{at}missouri.edu.

The intracellular mechanisms underlying enhanced myogenic contraction (MC) in coronary resistance arteries from exercise-trained (EX) pigs have not been established. The purpose of this study was to test the hypothesis that EX-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. Male Yucatan miniature swine were treadmill-trained (n=7) at ~75% of VO2max for 16 weeks (6 mph, 60 min) or remained sedentary (SED; n=6). Diameter measurements in response to intraluminal pressure (60, 75, 90 cmH20) or potassium chloride (KCl; 60 mM) were determined in single, cannulated resistance arteries (CRAs; ~100 µm ID) with and without the PKC inhibitor chelerythrine (CE; 1 µM). Confocal imaging of Ca2+ signaling (Cam) was also performed in CRAs of similar ID following 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 vs SED at 90 cmH20, as well as greater reductions in MC following CE at all pressures studied. At intraluminal pressures of 75 and 90 cmH20, CE produced greater decreases in Cam in CRAs from EX than SED (64% vs 25%; p<0.05). Inhibition of KCl constriction and Cam by CE was also greater in EX (p<0.05). Western blotting revealed significant increases in Ca2+-dependent PKC{alpha} (~50%) but not Ca2+-independent PKC{epsilon} levels in CRAs isolated from EX (p<0.05). We also observed significant group differences in phosphorylated-PKC{alpha} levels. Finally, voltage-gated Ca2+ current (VGCC) was effectively blocked by CE, bis-indolylmaleimide and staurosporine in isolated cells from CRAs, providing evidence for a mechanistic link between VGCCs and PKC in our experimental paradigm. These results suggest that enhanced MC by EX in CRAs involves PKC-dependent modulation of intracellular Ca2+, including regulation of VGCCs.




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