Ca2+ regulatory mechanisms of exercise protection against coronary artery disease in metabolic syndrome and diabetes.

Chronic exercise attenuates coronary artery disease (CAD) in humans largely independent of reductions in risk factors; thus major protective mechanisms of exercise are directly within the coronary vasculature. Further, tight control of diabetes, e.g., blood glucose, can be detrimental. Accordingly, knowledge of mechanisms by which exercise attenuates diabetic CAD could catalyze development of molecular therapies. Exercise attenuates CAD (atherosclerosis) and restenosis in miniature swine models, which enable precise control of exercise parameters (intensity, duration, and frequency) and characterization of the metabolic syndrome (MetS) and diabetic milieu. Intracellular Ca(2+) is a pivotal second messenger for coronary smooth muscle (CSM) excitation-contraction and excitation-transcription coupling that modulates CSM proliferation, migration, and calcification. CSM of diabetic dyslipidemic Yucatan swine have impaired Ca(2+) extrusion via the plasmalemma Ca(2+) ATPase (PMCA), downregulation of L-type voltage-gated Ca(2+) channels (VGCC), increased Ca(2+) sequestration by the sarcoplasmic reticulum (SR) Ca(2+) ATPase (SERCA), increased nuclear Ca(2+) localization, and greater activation of K channels by Ca(2+) release from the SR. Endurance exercise training prevents Ca(2+) transport changes with virtually no effect on the diabetic milieu (glucose, lipids). In MetS Ossabaw swine transient receptor potential canonical (TRPC) channels are upregulated and exercise training reverses expression and TRPC-mediated Ca(2+) influx with almost no change in the MetS milieu. Overall, exercise effects on Ca(2+) signaling modulate CSM phenotype. Future studies should 1) selectively target key Ca(2+) transporters to determine definitively their causal role in atherosclerosis and 2) combine mechanistic studies with clinical outcomes, e.g., reduction of myocardial infarction.