Activation of Ca2+-activated Cl–channels by store-operated Ca2+entry in arterial smooth muscle cells does not require reverse-mode Na+/Ca2+exchange

Abstract

The main purpose of this study was to characterize the stimulation of Ca2+-activated Cl–(ClCa) by store-operated Ca2+entry (SOCE) channels in rabbit pulmonary arterial smooth muscle cells (PASMCs) and determine if this process requires reverse-mode Na+/Ca2+exchange (NCX). In whole-cell voltage clamped PASMCs incubated with 1 μmol/L nifedipine (Nif) to inhibit Ca2+channels, 30 μmol/L cyclopiazonic acid (CPA), a SERCA pump inhibitor, activated a nonselective cation conductance permeable to Na+(ISOC) during an initial 1–3 s step, ranging from–120 to +60 mV, and Ca2+-activated Cl–current (ICl(Ca)) during a second step to +90 mV that increased with the level of the preceding hyperpolarizing step. Niflumic acid (100 μmol/L), a ClCachannel blocker, abolished ICl(Ca)but had no effect on ISOC, whereas the ISOCblocker SKF-96365 (50 μmol/L) suppressed both currents. Dual patch clamp and Fluo-4 fluorescence measurements revealed the appearance of CPA-induced Ca2+transients of increasing magnitude with increasing hyperpolarizing steps, which correlated with ICl(Ca)amplitude. The absence of Ca2+transients at positive potentials following a hyperpolarizing step combined with the observation that SOCE-stimulated ICl(Ca)was unaffected by the NCX blocker KB-R7943 (1 μmol/L) suggest that the SOCE/ClCainteraction does not require reverse-mode NCX in our conditions.