Ca(2+)-permeable large-conductance nonselective cation channels in rat basophilic leukemia cells

Spreading of Ca2+ signals in rat basophilic leukemia (RBL) cells occurs by release of ATP. Therefore we studied the effect of ATP on membrane currents. ATP (1-10 microM) activated large-conductance channels. Single channel events were resolved in the whole cell mode. Similar channel activity was observed in RBL cells transfected with the muscarinic M1 receptor after stimulation with carbachol as well as after intracellular infusion of aluminum fluoride. Activation was independent of internal Ca2+ (0-10 microM). The channels had a conductance of 250 pS in 135 mM Na+ and 70 pS in 100 mM Ca2+. The permeability (P) ratio was PCa/PNa/PCs/PMg = 16:1:0.6:0.6. These channels may contribute to secretory responses by allowing Ca2+ entry, leading to high Ca2+ concentrations in the vicinity of the channel pore.