CALCIUM-SENSITIVE CHLORIDE CHANNELS IN VASCULAR SMOOTH-MUSCLE CELLS

Chloride(Cl-) channels were characterized in vascular smooth muscle ce lls (VSMC) using radioisotope flux and patch-clamp electrophysiologica l techniques. Transmembrane (125)iodine (I-125) efflux from subculture d (Passage 1-5) rat aortic VSMCs was used as an indicator of Cl- movem ents to study the relationship between intracellular calcium concentra tion ([Ca2+](i)) and Cl- channel activity, Angiotensin II (Ang II) (10 (-7) M) and adenosine 5'-triphosphate (ATP) (10(-4) M) induced rapid i ncreases (9.7- and 14.9-fold, respectively) in I-125 efflux rates. We found that both Ang II- and ATP-stimulated I-125 efflux and [Ca2+](i) increases were completely abolished after brief incubation (20 mu M, 2 0 min) with the acetoxymethyl ester of ,2-bis(o-aminophenoxy)ethane-N, N,N',N'-tetraacetic acid (BAPTA-AM), a membrane-permeable Ca2+ chelato r. However, when external EGTA was used to blunt agonist-stimulated Ca 2+ influx, I-125 efflux was still increased in response to Ang II and ATP, These data suggest that Ca2+ release from intracellular sites is sufficient to activate Cl- channels in response to Ang II and ATP. Usi ng standard patch-clamp electrophysiological techniques, we found that Ang II, a Ca2+-mobilizing agonist, stimulated outward Cl- currents (g (Cl) = 75 pS) in cell-attached (C/A) patches of primary and subculture d VSMCs, Collectively, these data suggest that Ang II and other vasoco nstrictor agents stimulate Cl- channel activity via increases in [Ca2](i), Cl- channel activation may help to depolarize the VSMC membrane leading to increased Ca2+ influx during agonist stimulation.