Store-operated channels mediate Ca2+ influx and contraction in rat pulmonary artery

Cation channels activated by Ca2+ store depletion have been proposed to med iate Ca2+ influx in vascular smooth muscle cells. The aim of this study was to determine if store-operated channels have a functional role in pulmonar y artery smooth muscle cells (PASMCs). In intact rat pulmonary artery rings , cyclopiazonic acid (CPA) produced a sustained contraction that was resist ant to inhibition by nifedipine, but abolished in Ca2+-free solution and 50 % blocked in the presence of 6 mu mol/L Cd2+, 10 mu mol/L Ni2+, 600 mu mol/ L La3+, and 7 mu mol/L SKF96365. In freshly isolated PASMCs loaded with fur a-2, CPA increased the intracellular Ca2+ concentration by stimulating dihy dropyridine-resistant Ca2+ influx, which was approximate to 50% blocked by 10 mu mol/L Ni2+ and 7 mu mol/L SKF96365. In perforated-patch recordings, C PA activated a sustained inward current at negative membrane potentials, wh ich persisted in cells dialyzed with BAPTA, showed a near linear dependence on membrane potential when Cs+ was the main intracellular cation, and was blocked by Ni2+, Cd2+, and SKF96365 at concentrations preventing contractio n. The current showed a bimodal dependence on extracellular Ca2+, being enh anced 2-fold in the absence of Ca2+ and around 10-fold on reducing Ca from 1.8 to 0.2 mmol/L. RT-PCR revealed the expression of Trp1, Trp3, Trp4, Trp5 , and Trp6 mRNA, whereas immunostaining identified Trp1, Trp3, Trp4, and Tr p6 channel proteins in isolated PASMCs. At least one of these subunits may contribute to cation channels in PASMCs, which are activated by store deple tion to bring about Ca2+ influx and contraction.