Characteristics and regulation of a high conductance anion channel in GBK kidney epithelial cells.

Single anion selective channels have been studied in membrane patches of GBK cultured epithelial cells from bovine kidney. High conductance anion channels are exclusively observed in excised patches after holding them at membrane potentials larger than +/- 30 mV for seconds or minutes. Once activated, the channels show a steep voltage dependence, complex gating properties and multiple conductance levels. The major unit conductance is 300 pS (+/- 28; n = 12) in symmetrical chloride. The discrimination among different anions and between anions and cations is poor. The activity of the channels remains unchanged after addition of 10 mM EGTA to the cytoplasmic face of the membrane, but it is irreversibly inhibited by application of 1 mM 4-acetamido-4'-isothiocyano-2,2'-disulphonic acid stilbene (SITS). Neither permeabilization of the cell membrane to Ca2+ using the Ca2+ ionophore A23187, treatments which increase the cyclic AMP content of the cells, nor hypoosmotic shocks, activate high conductance anion channels in cell-attached patches in which the activity of the channels is subsequently demonstrated upon patch excision. These results indicate that high conductance anion channels with the same characteristics as those reported in different cell types are present in GBK cells and suggest that the physiological role for these molecular entities may be different from those previously postulated.