Potassium channels in cultured bovine adrenal chromaffin cells.
K channels of bovine adrenal chromaffin cells were studied using patch-clamp techniques. Whole-cell K currents measured near +10 mV were much larger in 1 mM-external Ca than in Ca-free saline. Noise analysis suggested that this Ca-dependent current was carried by a large unitary conductance channel, called BK channel, which was previously described in inside-out patches (Marty, 1981). The Ca-dependent K current near +10 mV declined with time due to 'run-down' of Ca channels. At the same time, a fraction of the outward current observed above +50 mV was also eliminated. This outward current component probably represents K efflux through Ca channels. Whole-cell Ca-dependent K currents were studied using various Ca buffers. EGTA buffers were surprisingly inefficient: in order to block the current entirely, it was necessary to use an isotonic EGTA solution and to increase internal pH. 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) was at least five times more efficient than EGTA. In isolated patches three types of single-channel K currents were observed. Under normal ionic conditions (140 mM-K inside, 140 mM-Na outside), the unitary conductances measured between -20 and +40 mV were 96 pS, 18 pS and 8 pS. The 96 pS channels are the Ca-dependent BK channels. 18 pS and 8 pS channels were both activated and then inactivated by membrane depolarization. Both displayed complex kinetics; single-channel currents were grouped in bursts. Activation and inactivation kinetics were faster for the 18 pS channel (therefore termed FK channel, for fast K channel) than for the 8 pS channel (SK channel, for slow or small amplitude channel). The voltage dependence of opening probability was steeper for the FK channel as compared to the SK channel.
A
A
Marty
E
E
Neher
D000200:Action Potentials / Q000187:drug effects; D000313:Adrenal Medulla / Q000166:cytology*; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002417:Cattle; D002478:Cells, Cultured; D002838:Chromaffin System / Q000166:cytology*; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D011188:Potassium / Q000502:physiology*; D013997:Time Factors
D007473:Ion Channels; D004533:Egtazic Acid; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D011188:Potassium; D002118:Calcium