Estimation of Na+ dwell time in the gramicidin A channel. Na+ ions as blockers of H+ currents.

Biochimica Et Biophysica Acta
S H Heinemann, F J Sigworth

Abstract

The permeation of Na+ through gramicidin A channels shows a simple saturation with increasing Na+ concentration that can be described by two different models. The first model assumes that one Na+ binds to the channel with high affinity (approximately 30 M-1) and that conduction occurs by a 'knock-on' mechanism requiring double occupancy of the channel; the other model assumes that Na+ binding is of low affinity (less than 1 M-1), and that double occupancy of the channel is rare. NMR measurements have shown tight Na+ binding, favoring the first model, but measurements of flux ratios and water transport support the second model. We present here a relatively model-independent measurement of the dwell time of Na+ inside the channel, in which we characterize the fluctuations in H+ current through the channel induced by 'block' from the more slowly permeating Na+ ions. The mean Na+ dwell time inside the channel is estimated to be approximately 10 ns at a membrane potential of 200 mV. This result is inconsistent with tight Na+ binding, thus favoring the second model.

References

Apr 1, 1980·Proceedings of the National Academy of Sciences of the United States of America·D W UrryM A Khaled

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Citations

Sep 2, 2009·The Journal of General Physiology·Miyuki KunoShigetoshi Oiki
Mar 10, 2016·Journal of the American Chemical Society·Yuka MatsukiShigetoshi Oiki
Sep 24, 1998·Biophysical Journal·T K RostovtsevaV A Parsegian
Jul 28, 1994·Nature·S M BezrukovV A Parsegian
Jan 1, 1991·Clinical Physics and Physiological Measurement : an Official Journal of the Hospital Physicists' Association, Deutsche Gesellschaft Für Medizinische Physik and the European Federation of Organisations for Medical Physics·R GraumannS Schneider
Oct 22, 1990·Proceedings. Biological Sciences·F G BallM S Sansom
Mar 29, 2003·Physiological Reviews·Thomas E Decoursey
Dec 26, 2001·Chemical Reviews·Hagan Bayley, Charles R. Martin
Apr 13, 2011·The Journal of Physical Chemistry. B·Carlos Marcelo G de Godoy, Samuel Cukierman

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