Our previous study demonstrated that multiple ion channels were heterogeneously expressed in human cardiac fibroblasts, including a large-conductance Ca(2+)-activated K(+) current (BKCa), a volume-sensitive chloride current (I(Cl.vol)), and voltage-gated sodium currents (I(Na)). The present study was designed to examine the possible involvement of these ion channels in proliferation of cultured human cardiac fibroblasts using approaches of cell proliferation assay, whole-cell patch voltage-clamp, siRNA and Western blot analysis. It was found that the blockade of BKCa with paxilline (1-3μM) or I(Cl.vol) with 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid disodium (DIDS, 100-200μM), but not I(Na) with tetrodotoxin (0.1-10μM), remarkably suppressed proliferation in human cardiac fibroblasts. Knockdown of KCa1.1 or Clcn3 with specific siRNAs significantly reduced BKCa or I(Cl.vol) current, mRNA and channel protein levels, and inhibited growth of human cardiac fibroblasts. Flow cytometry analysis showed accumulation of cardiac fibroblasts at G0/G1 phase and reduced cell number in S phase after inhibition of BKCa or I(Cl.vol) with channel blockers or knock down of the corresponding channels with specific siRNAs; these effects were accompanied by a decreased expression of cyclin D1 and cyclin E. The present results demonstrate the novel information that BKCa and I(Cl.vol) channels, but not I(Na) channels, are involved in the regulation of proliferation in cultured human cardiac fibroblasts by promoting cell cycle progression via modulating cyclin D1 and cyclin E expression.
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