Exercise training increases L-type calcium current density in coronary smooth muscle

Exercise training produces numerous adaptations in the coronary circulation, including an increase in coronary tone, both in conduit and resistance arteries. On the basis of the importance of voltage-gated Ca2+ channels (VGCC) in regulation of vascular tone, we hypothesized that exercise training would increase VGCC current density in coronary smooth muscle. To test this hypothesis, VGCC current was compared in smooth muscle from conduit arteries (>1.0 mm), small arteries (200-250 mu m), and large arterioles (75-150 mu m) from endurance-trained (Ex) or sedentary miniature swine (Sed). After 16-20 wk of treadmill training, VGCC current was determined using whole cell voltage-clamp techniques. In both Ex and Sed, VGCC current density was inversely related to arterial diameter, i.e., large arterioles > small arteries > conduit arteries. Exercise training increased peak inward currents approximately twofold in smooth muscle from all arterial sizes compared with those from Sed (large arteriole, -12.52 +/- 2.05 vs. -5.74 +/- 0.99 pA/pF; small artery, -6.20 +/- 0.97 vs. -3.18 +/- 0.44 pA/pF; and conduit arteries, -4.22 +/- 0.30 vs. -2.41 +/- 0.55 pA/pF; 10 mM Ba2+ external). Dihydropyridine sensitivity, voltage dependence, and inactivation kinetics identified this Ca2+ current to be L-type current in all arterial sizes from both Sed and Ex. Furthermore, peak VG;CC current density was correlated with treadmill endurance in all arterial sizes. We conclude that smooth muscle L-type Ca2+ current density is increased within the coronary arterial bed by endurance exercise training. This increased VGCC density may provide an important mechanistic link between functional and cellular adaptations in the coronary circulation to exercise training.