Ca2+-dependent Cl- channels in mouse and rabbit aortic smooth muscle cells:: regulation by intracellular Ca2+ and NO

Ca2+-dependent Cl- (Cl-Ca(-)) channels and their regulation by intracellular Ca2+ concentration ([Ca2+](i)) and nitric oxide (NO) were characterized in mouse and rabbit aortic smooth muscle cells (SMC) using patch clamp and fura 2 imaging. Single channels (1.8 pS) and whole cell Cl-Ca(-) currents were activated by caffeine-induced Ca2+ release. Single Cl-Ca(-) channels were also activated by greater than or equal to 200 nM Ca2+ in inside-out membrane patches and remained active for >5 min in less than or equal to 1 mu M Ca2+ but showed rapid rundown in 2 mM Ca2+. Authentic NO or S-nitroso-N-acetylpenicillamine (SNAP) did not affect their activation or rundown in inside-out patches. In the whole cell, SNAP (100 mu M) and 8-(4-chlorophenylthio)-guanosine 3',5'-cyclic monophosphate (50 mu M) did not affect Cl-Ca(-) current, but at a higher concentration SNAP (1 mM) induced a sustained [Ca2+]i rise, accompanied by a dramatic decrease in caffeine-induced Ca2+ release and Cl-Ca(-) current. These results indicate that 1) mouse and rabbit aortic SMC possess 1.8-pS Cl-Ca(-) channels that are activated by Ca2+ release from the stores, 2) both activation and rundown of single Cl-Ca(-), channels depend on [Ca2+](i), and 3) NO does not affect Cl-Ca(-) channels directly or via cGMP but can inhibit their activation indirectly by decreasing Ca2+ release from the stores.