Store‐operated Ca2+ entry (SOCE) and canonical transient receptor potential channel (TRPC) proteins are expressed in rat distal pulmonary venous smooth muscle

Abstract

Chronic hypoxia causes remodeling and alters contractile responses in both pulmonary arteries (PA) and pulmonary veins (PV). Although PA have been studied extensively in this disorder, the mechanisms by which PV respond to hypoxia and whether these responses contribute to chronic hypoxic pulmonary hypertension (CHPH) remain poorly understood. In pulmonary arterial smooth muscle, we have previously demonstrated that influx of Ca2+ through store‐operated calcium channels (SOCC) thought to be composed of TRPC proteins is likely to play an important role in development of CHPH. To determine whether this mechanism could also be operative in pulmonary venous smooth muscle, we measured intracellular Ca2+ concentration ([Ca2+]i) by fura‐2 fluorescence microscopy in primary cultures of pulmonary venous smooth muscle cells (PVSMC) isolated from rat distal PV. In cells perfused with Ca2+‐free media containing cyclopiazonic acid (10 µM) and nifedipine (5 µM) to deplete SR Ca2+ stores and block voltage‐dependent Ca2+ channels, restoration of extracellular Ca2+ caused marked increases in [Ca2+]i whereas MnCl2 (200 µM) quenched fura‐2 fluorescence, indicating SOCE. SKF‐96365 and NiCl2, antagonists of SOCC, blocked SOCE at concentrations that did not alter Ca2+ responses to 60 mM KCl. Real‐time PCR revealed mRNA expression of TRPC1, ‐4, and ‐6, and Western blotting confirmed protein expression of TRPC1, ‐4, and ‐6 in both rat de‐endolthelialized distal PV and PVSMC. Our results suggest that SOCE through Ca2+ channels composed of TRPC proteins could contribute to Ca2+ signaling in distal PVSMC.