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

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⁺ (Ca_m)] was also performed in CRAs of similar internal diameter after abluminal loading of the Ca ²⁺ 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 Ca_m in CRAs from EX than from SED animals (64% vs. 25%, P < 0.05). Inhibition of KCl constriction and C_am by CE was also greater in EX animals (P < 0.05). Western blotting revealed significant increases in Ca²⁺-dependent PKC-α (∼50%) but not Ca²⁺-independent PKC-ε levels in CRAs isolated from EX animals (P < 0.05). We also observed significant group differences in phosphorylated PKC-α 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.