The Functional Surface Charge Density of a Fast K Channel in the Myelinated Axon of Xenopus laevis

The Functional Surface Charge Density of a Fast K Channel in the Myelinated Axon of Xenopus laevis The action of Mg2+ on the putative xKv1.1 channel in the myelinated axon of Xenopus laevis was analyzed in voltage clamp experiments. The main effect was a shift in positive direction of the open probability curve (16 mV at 20 mm Mg2+), calculated from measurements of the instantaneous current at Na reversal potential after 50–100 msec steps to different potentials. The shift was measured at an open probability level of 25% to separate it from shifts of other K channel populations in the nodal region. The results could be explained in terms of screening effects on fixed charges located on the surface of the channel protein. Using the Grahame equation the functional charge density was estimated to −0.45 e nm−2. Analyzing this value, together with previously estimated values from other K channels, with reference to the charge of different extracellular loops of the channel protein, we conclude that the loop between the transmembrane S5 segment and the pore forming P segment determines the functional charge density of voltage-gated K channels. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The Journal of Membrane Biology Springer Journals

The Functional Surface Charge Density of a Fast K Channel in the Myelinated Axon of Xenopus laevis

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Publisher
Springer-Verlag
Copyright
Copyright © Inc. by 1998 Springer-Verlag New York
Subject
Life Sciences; Biochemistry, general; Human Physiology
ISSN
0022-2631
eISSN
1432-1424
D.O.I.
10.1007/s002329900431
Publisher site
See Article on Publisher Site

Abstract

The action of Mg2+ on the putative xKv1.1 channel in the myelinated axon of Xenopus laevis was analyzed in voltage clamp experiments. The main effect was a shift in positive direction of the open probability curve (16 mV at 20 mm Mg2+), calculated from measurements of the instantaneous current at Na reversal potential after 50–100 msec steps to different potentials. The shift was measured at an open probability level of 25% to separate it from shifts of other K channel populations in the nodal region. The results could be explained in terms of screening effects on fixed charges located on the surface of the channel protein. Using the Grahame equation the functional charge density was estimated to −0.45 e nm−2. Analyzing this value, together with previously estimated values from other K channels, with reference to the charge of different extracellular loops of the channel protein, we conclude that the loop between the transmembrane S5 segment and the pore forming P segment determines the functional charge density of voltage-gated K channels.

Journal

The Journal of Membrane BiologySpringer Journals

Published: Sep 15, 1998

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