Activity of Ca -activated Cl channels contributes to regulating receptor- and store-operated Ca 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 muM), flufenamic acid (100 muM), and 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (100 muM). 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 muM cyclopiazonic acid. In addition, ROCE and SOCE were abolished by SKF-96365 (50 muM) and 2-aminoethyl diphenylborinate (100 muM), and were slightly decreased in the presence of diltiazem (10 muM). 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

Enhanced Ca2+-sensing Receptor Function in Idiopathic Pulmonary Arterial Hypertension

Rationale: A rise in cytosolic Ca2+ concentration ([Ca2+]cyt) in pulmonary arterial smooth muscle cells (PASMC) is an important stimulus for pulmonary vasoconstriction and vascular remodeling. Increased resting [Ca2+]cyt and enhanced Ca2+ influx have been implicated in PASMC from patients with idiopathic pulmonary arterial hypertension (IPAH). Objective: We examined whether the extracellular Ca2+-sensing receptor (CaSR) is involved in the enhanced Ca2+ influx and proliferation in IPAH-PASMC and whether blockade of CaSR inhibits experimental pulmonary hypertension. Methods and Results: In normal PASMC superfused with Ca2+-free solution, addition of 2.2 mM Ca2+ to the perfusate had little effect on [Ca2+]cyt. In IPAH-PASMC, however, restoration of extracellular Ca2+ induced a significant increase in [Ca2+]cyt. Extracellular application of spermine also markedly raised [Ca2+]cyt in IPAH-PASMC, but not in normal PASMC. The calcimimetic R568 enhanced, whereas the calcilytic NPS 2143 attenuated, the extracellular Ca2+-induced [Ca2+]cyt rise in IPAH-PASMC. Furthermore, the protein expression level of CaSR in IPAH-PASMC was greater than in normal PASMC; knockdown of CaSR in IPAH-PASMC with siRNA attenuated the extracellular Ca2+-mediated [Ca2+]cyt increase and inhibited IPAH-PASMC proliferation. Using animal models of pulmonary hypertension, our data showed that CaSR expression and function were both enhanced in PASMC, whereas intraperitoneal injection of the calcilytic NPS 2143 prevented the development of pulmonary hypertension and right ventricular hypertrophy in rats injected with monocrotaline and mice exposed to hypoxia. Conclusions: The extracellular Ca2+-induced increase in [Ca2+]cyt due to upregulated CaSR is a novel pathogenic mechanism contributing to the augmented Ca2+ influx and excessive PASMC proliferation in patients and animals with pulmonary arterial hypertension