Regulation of Proliferation and Membrane Potential by Chloride Currents in Rat Pulmonary Artery Smooth Muscle Cells

Pulmonary artery smooth muscle cell (PASMC) proliferation contributes to increased pulmonary vascular resistance and pulmonary hypertension. Because proliferation depends on membrane potential (V(m)) and because V(m) is, in part, determined by Cl(-) currents (I(Cl)), we examined the effects of I(Cl) inhibition with 4,4;-diisothiocyanatostilbene-2,2;-disulfonic acid (DIDS) on cultured rat PASMCs. DIDS (30 mumol/L) reduced cell numbers, decreased 5-bromodeoxyuridine incorporation and delayed cell cycle progression. I(Cl) inhibition with 5-Nitro-2-(3-phenylpropylamino) benzoic acid (100 mumol/L) also reduced cell numbers of cultured rat PASMCs. To test the possible involvement of I(Cl) in the regulation of PASMC proliferation, we measured V(m) and I(Cl) in both cultured (proliferating) and acutely dissociated (nonproliferating) rat PASMCs. V(m) (-39.3+/-1.4 mV) was close to the equilibrium potential of Cl(-) (-39 mV) in proliferating PASMCs but differed from equilibrium potential of Cl(-) in acutely dissociated cells (-45.3+/-0.9 mV). DIDS and substitution of extracellular Cl(-) with I(-) induced V(m) hyperpolarization in proliferating but not nonproliferating PASMCs. Consistent with V(m) recordings, DIDS-sensitive baseline and swelling-activated (Ca(2+)-independent) I(Cl)s, recorded with low Ca(2+) (<1 nmol/L) pipette solutions, were approximately 5-fold greater in proliferating than in nonproliferating PASMCs. By contrast, Ca(2+)-activated I(Cl) did not differ between proliferating and nonproliferating PASMCs. Ca(2+)-independent I(Cl)s were also increased in proliferating PASMCs acutely dissociated from rats exposed to hypoxia (10% O(2); 7 days). These findings are consistent with the conclusion that I(Cl)s regulate proliferation of PASMCs and suggest that selective I(Cl) inhibition may be useful in treating pulmonary hypertension.