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Conductance properties of single inwardly rectifying potassium channels in ventricular cells from guinea‐pig heart.

Conductance properties of single inwardly rectifying potassium channels in ventricular cells from... Single ventricular cells were enzymatically isolated from adult guinea‐pig hearts (Isenberg & Klöckner, 1982). The patch‐clamp technique (Hamill, Marty, Neher, Sakmann & Sigworth, 1981) was used to examine the conductance properties of an inward‐rectifying K+ channel present in their sarcolemmal membrane. When the K+ concentration on the extracellular side of the patch was between 10.8 and 300 mM, inward current steps were observed at potentials more negative than the K+ equilibrium potential (EK). At more positive potentials no current steps were detectable, demonstrating the strong rectification of the channel. The zero‐current potential extrapolated from the voltage dependence of the inward currents depends on the external K4 concentration (K+)o in a fashion expected for a predominantly K+‐selective ion channel. It is shifted by 49 mV for a tenfold change in (K+)o. The conductance of the channel depends on the square root of (K+)o. In approximately symmetrical transmembrane K+ concentrations (145 mM‐external K+), the single‐channel conductance is 27 pS (at 19‐23 degrees C). In normal Tyrode solution (5.4 mM‐external K+) we calculate a single‐channel conductance of 3.6 pS. The size of inward current steps at a fixed negative membrane potential V increases with (K+)o. The relation between step size and (K+)o shows saturation. Assuming a Michaelis‐Menten scheme for binding of permeating K+ to the channel, an apparent binding constant of 210 mM is calculated for a membrane potential of ‐100 mV. For this potential the current at saturating (K+)o is estimated as 6.5 pA. The rectification of the single‐channel conductance at membrane potentials positive to EK occurs within 1.5 ms of stepping the membrane potential from a potential of high conductance to one of low conductance. In addition to the main conductance state, the channel can adopt several substates of conductance. The main state could be the result of the simultaneous opening of four conducting subunits, each of which has a conductance of about 7 pS in 145 mM‐external K+. The density of the inward‐rectifying K+ channels in the ventricular sarcolemma is 0‐10 channel/10 micron2 of surface membrane; the average of twenty‐eight patches was 1 channel/1.8 micron2. It is concluded that the inward‐rectifying K+ channels mediate the resting K+ conductance of ventricular heart muscle and the current termed IK1 in conventional voltage‐clamp experiments. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The Journal of Physiology Wiley

Conductance properties of single inwardly rectifying potassium channels in ventricular cells from guinea‐pig heart.

The Journal of Physiology , Volume 347 (1) – Feb 1, 1984

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References (35)

Publisher
Wiley
Copyright
© 2014 The Physiological Society
ISSN
0022-3751
eISSN
1469-7793
DOI
10.1113/jphysiol.1984.sp015088
Publisher site
See Article on Publisher Site

Abstract

Single ventricular cells were enzymatically isolated from adult guinea‐pig hearts (Isenberg & Klöckner, 1982). The patch‐clamp technique (Hamill, Marty, Neher, Sakmann & Sigworth, 1981) was used to examine the conductance properties of an inward‐rectifying K+ channel present in their sarcolemmal membrane. When the K+ concentration on the extracellular side of the patch was between 10.8 and 300 mM, inward current steps were observed at potentials more negative than the K+ equilibrium potential (EK). At more positive potentials no current steps were detectable, demonstrating the strong rectification of the channel. The zero‐current potential extrapolated from the voltage dependence of the inward currents depends on the external K4 concentration (K+)o in a fashion expected for a predominantly K+‐selective ion channel. It is shifted by 49 mV for a tenfold change in (K+)o. The conductance of the channel depends on the square root of (K+)o. In approximately symmetrical transmembrane K+ concentrations (145 mM‐external K+), the single‐channel conductance is 27 pS (at 19‐23 degrees C). In normal Tyrode solution (5.4 mM‐external K+) we calculate a single‐channel conductance of 3.6 pS. The size of inward current steps at a fixed negative membrane potential V increases with (K+)o. The relation between step size and (K+)o shows saturation. Assuming a Michaelis‐Menten scheme for binding of permeating K+ to the channel, an apparent binding constant of 210 mM is calculated for a membrane potential of ‐100 mV. For this potential the current at saturating (K+)o is estimated as 6.5 pA. The rectification of the single‐channel conductance at membrane potentials positive to EK occurs within 1.5 ms of stepping the membrane potential from a potential of high conductance to one of low conductance. In addition to the main conductance state, the channel can adopt several substates of conductance. The main state could be the result of the simultaneous opening of four conducting subunits, each of which has a conductance of about 7 pS in 145 mM‐external K+. The density of the inward‐rectifying K+ channels in the ventricular sarcolemma is 0‐10 channel/10 micron2 of surface membrane; the average of twenty‐eight patches was 1 channel/1.8 micron2. It is concluded that the inward‐rectifying K+ channels mediate the resting K+ conductance of ventricular heart muscle and the current termed IK1 in conventional voltage‐clamp experiments.

Journal

The Journal of PhysiologyWiley

Published: Feb 1, 1984

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