CHARACTERIZATION OF VOLUME-SENSITIVE TAURINE-PERMEABLE AND CL--PERMEABLE CHANNELS

Volume-sensitive Cl- channels [I-Cl(vol)] were studied using taurine e fflux and patch-clamp experiments in 9HTEo(-) human tracheal cells. Ce lls were stimulated with the Ca2+-elevating agents ATP and ionomycin i n isotonic medium or in hypotonic solutions. ATP (100 mu M) or ionomyc in (1 mu M) and hypotonic shock produced a synergic effect. Indeed, th e resulting taurine efflux was much higher than the sum of the single effects elicited by ATP, ionomycin, or hypotonic medium. The taurine r elease elicited by hypotonic shock and the potentiation by ATP and ion omycin were markedly inhibited by using a Ca2+-free extracellular medi um and by incubating the cells with the membrane-permeable 1,2-bis(2-a minophenoxy)ethane=N,N,N' ,N'-tetraacetic acid acetoxymethyl ester che lating agent. Patch-clamp experiments confirmed the role of Ca2+ on I- Cl(vol) channels. Swelling-induced taurine efflux was inhibited by rea ctive blue 2, suramin, and pyridoxal-phosphate-6-azophenyl-2',4'-disul fonic acid. Patch-clamp experiments demonstrated that these compounds shift the voltage-dependent inactivation of I-Cl(vol) channels toward more negative values. This study indicates that tile sensitivity of I- Cl(vol) to cell volume changes is modulated by intracellular Ca2+ and that purinergic receptor antagonists represent a new class of Cl- chan nel blockers.