Role of Cl− currents in rat aortic smooth muscle activation by prostaglandin F2α

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.

Pleiotropic Effects of Hydrogen Peroxide in Arteries and Veins From Normotensive and Hypertensive Rats

Hydrogen peroxide causes vascular contraction and relaxation and contributes to the pathogenesis of hypertension. We hypothesized that the contractile state of blood vessels governs whether H 2 O 2 causes contraction or relaxation. Hydrogen peroxide (1 μmol/L to 1 mmol/L) concentration-dependently contracted thoracic aorta and vena cava from sham normotensive and deoxycorticosterone acetate (DOCA)-salt hypertensive rats. The maximal contraction to H 2 O 2 was 3 times greater in DOCA aorta compared with sham aorta but unchanged in DOCA vena cava compared with sham vena cava. In prostaglandin F 2α (20 μmol/L)–contracted aorta and vena cava from sham and DOCA rats, H 2 O 2 (1 μmol/L to 1 mmol/L) induced a concentration-dependent relaxation that was impaired in DOCA aorta but not DOCA vena cava. In contrast, in KCl (30 mmol/L)-contracted vessels, maximal H 2 O 2 -induced contraction was enhanced 15-fold in sham aorta and 5-fold in DOCA aorta but only 2-fold in sham vena cava. Tetraethylammonium (10 mmol/L), BAY K 8644 (100 nmol/L), and ouabain (1 mmol/L) all enhanced maximal aortic H 2 O 2 -induced contraction, whereas only ouabain enhanced venous H 2 O 2 -induced contraction. The removal of extracellular Ca 2+ reduced H 2 O 2 -induced contraction in KCl-contracted aorta, whereas maximal venous H 2 O 2 -induced contraction (under basal conditions) was unchanged. Our data suggest that differences in arterial and venous K + channel activity and extracellular Ca 2+ influx are responsible for differences in arterial and venous contraction to H 2 O 2 . In DOCA-salt hypertension, arterial but not venous contraction to H 2 O 2 is enhanced, and relaxation to H 2 O 2 is reduced.