TRPC1, STIM1 and Orai1 Mediate Capacitative Calcium Entry Activated by Acute Hypoxia in Mouse Pulmonary Arterial Smooth Muscle Cells

Abstract

Previous studies in pulmonary artery smooth muscle cells (PASMCs) showed that acute hypoxia activates capacitative Ca2+ entry (CCE) but the molecular channel(s) and the molecular signal(s) mediating CCE caused by acute hypoxia remain unclear. The present study aimed to determine if TRPC1, STIM1 and Orai1 mediate CCE caused by acute hypoxia in mouse PASMCs. In primary cultured PASMCs loaded with fura-2, acute hypoxia caused a transient followed by a sustained rise in intracellular Ca2+ concentration ([Ca2+]i). The transient but not sustained rise in [Ca2+]i was partially inhibited by nifedipine. In addition, acute hypoxia increased the rate of Mn2+ quench of fura-2 fluorescence that was inhibited by SKF 96365, Ni2+, La3+ and Gd3, exhibiting pharmacological properties characteristic of CCE. The nifedipine-insensitive rise in [Ca2+]i and the increase in Mn2+ quench rate were both inhibited in cells pretreated with antibodies raised against extracellular epitopes of TRPC1, in cells transfected with STIM1 siRNA and in cells transfected with Orai1 siRNA. Taken together, acute hypoxia causes activation of voltage-operated Ca2+ entry and CCE. These data suggest that TRPC1, STIM1 and Orai1 mediate CCE activated by acute hypoxia in mouse PASMCs. [Supported by HL49254, NCRR P20RR15581 (JR Hume) and AHA Scientist Development Grant (LC Ng)]