TRPC1 and STIM1 Mediate Capacitative Calcium Entry in Mouse Pulmonary Arterial Smooth Muscle Cells

Abstract

Previous studies in pulmonary arterial smooth muscle cells (PASMCs) showed that TRPC1 channel mediates capacitative Ca2+ entry (CCE) but the molecular signal(s) that activate TRPC1 in PASMCs remains unknown. The aim of the present study was to determine if TRPC1 mediate CCE through activation of STIM1 protein in mouse PASMCs. In primary cultured PASMCs loaded with fura‐2, 10μM CPA caused a rise in [Ca2+]i but it was abolished when extracellular Ca2+ was removed. Subsequent addition of 2mM Ca2+ elicited a transient rise in [Ca2+]i that was partially inhibited by 10μM nifedipine, leaving a nifedipine‐insensitive transient and nifedipine‐insensitive sustained rise in [Ca2+]i. The nifedipine‐insensitive sustained, but not transient rise in [Ca2+]i was inhibited in cells pretreated with antibodies raised against extracellular epitope of TRPC1 and STIM1. RT‐PCR revealed TRPC1 and STIM1 mRNAs, whereas Western blot analysis identified TRPC1 and STIM1 proteins in cultured mouse PASMCs. Taken together, store‐depletion causes activation of voltage‐operated Ca2+ entry, CCE and another as yet unidentified voltage‐independent Ca2+ entry pathway. These data suggest that CCE is mediated by TRPC1 channel possibly through activation of STIM1 protein in mouse PASMCs. (Supported by HL49254 and NCRR P20RR15581)