Activity of Ca 2+ ‐Activated Cl − Channels Contributes to Regulating Receptor‐ and Store‐Operated Ca 2+ Entry in Human Pulmonary Artery Smooth Muscle Cells

Intracellular Ca 2+ plays a fundamental role in regulating cell functions in pulmonary arterial smooth muscle cells (PASMCs). A rise in cytosolic Ca 2+ concentration ([Ca 2+ ] cyt ) triggers pulmonary vasoconstriction and stimulates PASMC proliferation. [Ca 2+ ] cyt is increased mainly by Ca 2+ release from intracellular stores and Ca 2+ influx through plasmalemmal Ca 2+ ‐permeable channels. Given the high concentration of intracellular Cl − in PASMCs, Ca 2+ ‐activated Cl − (Cl Ca ) channels play an important role in regulating membrane potential and cell excitability of PASMCs. In this study, we examined whether activity of Cl Ca channels was involved in regulating [Ca 2+ ] cyt in human PASMCs via regulating receptor‐ (ROCE) and store‐ (SOCE) operated Ca 2+ entry. The data demonstrated that an angiotensin II (100 nM)‐mediated increase in [Ca 2+ ] cyt via ROCE was markedly attenuated by the Cl Ca channel inhibitors, niflumic acid (100 µM), flufenamic acid (100 µM), and 4,4′‐diisothiocyanatostilbene‐2,2′‐disulfonic acid (100 µM). The inhibition of Cl Ca channels by niflumic acid and flufenamic acid significantly reduced both transient and plateau phases of SOCE that was induced by passive depletion of Ca 2+ from the sarcoplasmic reticulum by 10 µM cyclopiazonic acid. In addition, ROCE and SOCE were abolished by SKF‐96365 (50 µM) and 2‐aminoethyl diphenylborinate (100 µM), and were slightly decreased in the presence of diltiazem (10 µM). The electrophysiological and immunocytochemical data indicate that Cl Ca currents were present and TMEM16A was functionally expressed in human PASMCs. The results from this study suggest that the function of Cl Ca channels, potentially formed by TMEM16A proteins, contributes to regulating [Ca 2+ ] cyt by affecting ROCE and SOCE in human PASMCs.