Activation of Ca 2+-activated Cl - channels by store-operated Ca 2+ entry in arterial smooth muscle cells does not require reverse-mode Na +/Ca 2+ exchange

摘要

The main purpose of this study was to characterize the stimulation of Ca 2+-activated Cl - (Cl Ca) by store-operated Ca 2+ entry (SOCE) channels in rabbit pulmonary arterial smooth muscle cells (PASMCs) and determine if this process requires reverse-mode Na +/Ca 2+ exchange (NCX). In whole-cell voltage clamped PASMCs incubated with 1 μmol/L nifedi-pine (Nif) to inhibit Ca 2+ channels, 30 mmol/L cyclopiazonic acid (CPA), a SERCA pump inhibitor, activated a nonselective cation conductance permeable to Na + (I SOC) during an initial 1-3 s step, ranging from-120 to +60 mV, and Ca 2+-activated Cl - current (I Cl(Ca)) during a second step to +90 mV that increased with the level of the preceding hyperpola-rizing step. Niflumic acid (100 μmol/L), a Cl Ca channel blocker, abolished I Cl(Ca) but had no effect on I SOC, whereas the I SOC blocker SKF-96365 (50 μmol/L) suppressed both currents. Dual patch clamp and Fluo-4 fluorescence measurements revealed the appearance of CPA-induced Ca 2+ transients of increasing magnitude with increasing hyperpolarizing steps, which correlated with I Cl(Ca) amplitude. The absence of Ca 2+ transients at positive potentials following a hyperpolarizing step combined with the observation that SOCE-stimulated I Cl(Ca) was unaffected by the NCX blocker KB-R7943 (1 μmol/L) suggest that the SOCE/Cl Ca interaction does not require reverse-mode NCX in our conditions.