Contribution of ASIC to Increased Pulmonary Vascular Smooth Muscle Resting [Ca 2+]i and Store‐Operated Ca2+ Entry Following Chronic Hypoxia

Abstract

Increases in basal pulmonary vascular smooth muscle (VSM) intracellular Ca2+([Ca2+]i) and store‐operated Ca2+ entry (SOCE) have been implicated in mediating the vasoconstrictor and arterial remodeling components of chronic hypoxia (CH)‐induced pulmonary hypertension. The goal of the present study was to characterize a role for the unique class of ion channels, acid sensing ion channels (ASICs), in regulating basal VSM [Ca2+]i and SOCE in the hypertensive pulmonary circulation. We hypothesized that enhanced Ca2+ entry through ASIC contributes to elevated basal VSM [Ca2+]i and increased SOCE following CH. Inhibition of ASIC with amiloride or benzamil attenuated SOCE and associated vasoconstriction in fura‐2‐loaded, endothelium‐disrupted, pressurized small pulmonary arteries from control rats. Furthermore, siRNA knockdown of ASIC1, but not ASIC2 or ‐3, diminished SOCE in primary cultures of rat pulmonary VSM cells. Resting [Ca2+]i and SOCE were enhanced in isolated small pulmonary arteries from CH rats (4 wk at 0.5 atm) vs. controls. Benzamil reduced basal [Ca2+]i in arteries from both groups, but caused a greater reduction in resting [Ca2+]i in arteries from CH rats compared to controls. In addition, benzamil attenuated the increase in SOCE in CH arteries and normalized responses between groups. Consistent with these findings, CH upregulated pulmonary vascular ASIC1, but not ASIC2 or ‐3 expression as determined by Western blotting. These studies support a novel role of ASIC to mediate elevated basal VSM [Ca2+]i and increased SOCE following CH.