Calcium channel blockade limits transcriptional, translational and functional up-regulation of the cardiac calpain system after myocardial infarction

Abnormal Ca 2+ inward current through cardiac Ca 2+ channels during ischemia has been shown to be an initial signal for activation of myocardial Ca 2+-dependent enzymes. This study investigated the contribution of cardiac L- and T-type Ca 2+ channels in the calpain-mediated myocardial damage following myocardial infarction. Myocardial infarction was induced by permanent ligation of the left coronary artery. Infarcted rats were orally treated with placebo, amlodipine (L-channel blockade; 4 mg/kg/day) or mibefradil (L-/T-channel blockade; 10 mg/kg/day) beginning 7 days before induction of myocardial infarction. Gene expression, protein levels and enzyme activity of calpains I and II were measured 1, 3, 7 and 14 days postcoronary occlusion in the noninfarcted and infarcted myocardium. Infarct size, left ventricular dilation and interstitial collagen volume fraction were determined in picrosirius red-stained hearts. Myocardial infarction induced an up-regulation of calpain I mRNA, protein and activity in the noninfarcted myocardium (maximum 14 days postinfarction), whereas mRNA, protein and activity of calpain II were maximally increased in the infarcted myocardium 3 days postinfarction. Fourteen days postinfarction, infarct size was 49%, the left ventricle was dilated and interstitial collagen volume fraction was increased. Amlodipine-inhibited mRNA, protein and activity up-regulation of calpain I decreased interstitial collagen volume fraction and infarct size. Mibefradil-attenuated mRNA, protein and activity up-regulation of calpain II at all four time points measured and of calpain I at 7 and 14 days postinfarction reduced infarct size and prevented left ventricular dilation. Infarction-induced cardiac hypertrophy was accompanied by an up-regulation of calpain I, whereas calpain II was up-regulated in the infarcted myocardium. Cardiac L- and T-type Ca 2+ channel blockade differentially reduced postinfarction remodeling associated with selective inhibition of cardiac calpains I and II, respectively.