Potassium channels in cultured bovine adrenal chromaffin cells.

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. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The Journal of Physiology Wiley

Potassium channels in cultured bovine adrenal chromaffin cells.

The Journal of Physiology, Volume 367 (1) – Oct 1, 1985

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Publisher
Wiley
Copyright
© 2014 The Physiological Society
ISSN
0022-3751
eISSN
1469-7793
DOI
10.1113/jphysiol.1985.sp015817
Publisher site
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Abstract

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.

Journal

The Journal of PhysiologyWiley

Published: Oct 1, 1985

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