Hypercholesterolemia inhibits L-type calcium current in coronary macro-, not microcirculation

Hypercholesterolemia (HC) is a mary risk factor for the development of coronary heart disease. Coronary ion regulation, especially calcium, is thought to be important in coronary heart disease development; however, the influence of high dietary fat and cholesterol on coronary arterial smooth muscle (CASM) ion channels is unknown. The purpose of this study was to determine the effect of diet-induced HC on CASM voltage-gated calcium current (I(Ca)). Male miniature swine were fed a high-fat, high-cholesterol diet (40% kcal fat, 2% wt cholesterol) for 20-24 wk, resulting in elevated serum total and low-density lipoprotein cholesterol. Histochemistry indicated early atherosclerosis in large coronary arteries. CASM were isolated from the right coronary artery (>1.0 mm ID), small arteries ( approximately 200 microm), and large arterioles ( approximately 100 microm). I(Ca) was determined by whole cell voltage clamp. L-type I(Ca) was reduced approximately 30% by HC compared with controls in the right coronary artery (-5.29 +/- 0.42 vs. -7.59 +/- 0.41 pA/pF) but not the microcirculation (small artery, -8.39 +/- 0.80 vs. -10.13 +/- 0.60; arterioles, -10.78 +/- 0.93 vs. -11.31 +/- 0.95 pA/pF). Voltage-dependent activation was unaffected by HC in both the macro- and microcirculation. L-type voltage-gated calcium channel (Ca(v)1.2) mRNA and membrane protein levels were unaffected by HC. Inhibition of I(Ca) by HC was reversed in vitro by the cholesterol scavenger methyl-beta-cyclodextrin and mimicked in control CASM by incubation with the cholesterol donor cholesterol:methyl-beta-cyclodextrin. These data indicate that CASM L-type I(Ca) is decreased in large coronary arteries in early stages of atherosclerosis, whereas I(Ca) in the microcirculation is unaffected. The inhibition of calcium channel activity in CASM of large coronary arteries is likely due to increases in membrane free cholesterol.