Increased expression of L-type calcium channels in vascular smooth muscle cells at spastic site in a porcine model of coronary artery spasm

Coronary artery spasm is caused primarily by increased contractility of vascular smooth muscle. Excessive Ca²⁺ entry into vascular smooth muscle cells (VSMCs) may be one of the key mechanisms for the spasm, but no study has ever directly examined the possible alterations of Ca²⁺ channels in the spastic coronary artery. Here we show that L-type Ca²⁺ channels are excessively expressed at the spastic site of the coronary artery. In a porcine model of coronary spasm with balloon injury, both receptor-mediated stimulation of L-type Ca²⁺ channels by serotonin and direct stimulation of the channels by Bay K 8644 (a dihydropyridine Ca²⁺ channel agonist) repeatedly induced coronary spasm in vivo, which was abolished by pretreatment with nifedipine, a dihydropyridine Ca²⁺ channel antagonist. In a single VSMC freshly dispersed from coronary arteries in vitro, patch-clamp experiments showed that current density of L-type Ca²⁺ channel current was significantly increased in VSMCs from the spastic site compared with that from the control site even when the channels were maximally stimulated by Bay K 8644. There was no difference in the sensitivity of the channels to Bay K 8644. These result-indicate that functionally available L-type Ca²⁺ channels are excessively expressed at the spastic site of the coronary artery in our porcine model, suggesting that increased expression of L-type Ca²⁺ channels and concomitant increase in Ca²⁺ entry into VSMCs through the channels may contribute, at least in part, to the pathogenesis of coronary artery spasm.