Activation of single Ca2(+)-dependent K+ channel by external ATP in mouse macrophages

Single Ca2(+)-dependent K+ currents responding to external ATP were recorded from cell-attached patches on mouse peritoneal macrophages. Extracellularly applied ATP activated an inward single-channel current with a conductance of 25 pS and a reversal potential of -79 mV (pipette potential, Vp) when the pipette contained a 145 mM KCl solution. The reversal potential was shifted 56 mV positive by a 10-fold reduction in external (pipette) K+ concentration. The effect of ATP was abolished by either removal of external Ca2+ or treatment with an intracellular Ca2+ chelator, the acetoxymethyl ester of 1,2-bis (2-aminophenoxy)ethane-N,N,N'N'-tetraacetic acid (BAPTA-AM). This channel has a mean open time of 9.1 ms and open probability was not strongly dependent on Vp in the range tested (+120 to -30 mV).