Biophysical Journal 66: 1864-1878 (1994)
© 1994 the Biophysical Society

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Correa, A M Articles by Bezanilla, F Search for Related Content PubMed PubMed Citation Articles by Correa, A M Articles by Bezanilla, F

Gating of the squid sodium channel at positive potentials: II. Single channels reveal two open states.

Department of Physiology, School of Medicine, University of California at Los Angeles 90024.

ABSTRACT

Single-channel recordings from squid axon Na+ channels were made under conditions of reverse sodium gradient. In the range of potentials studied, +40-(+)120 mV, channels opened promptly after depolarization, closed and reopened several times during the pulse. In patches containing only one channel, the distributions of open dwell times showed two components showing the existence of a second open state. The ensemble average of single-channel records showed incomplete inactivation that became more pronounced at more positive potentials, showing that the maintained phase of the current is the result of only one type of sodium channel with two open states. Analysis of bursts indicated that the dwell times of the events at the onset of the depolarization are longer than those later in the pulse. The dwell open times of the first events could be fitted with a single exponential. This indicated that the channels open preferentially through the first open state, the access to the second open state happening subsequently. Maximum likelihood analysis was used to evaluate several possible kinetic schemes incorporating a second open state. The best model to fit the data from single channels, and consistent with the data from macroscopic and gating currents, has a second open state evolving from the inactivated state. A kinetic model is proposed that incorporates information obtained from dialyzed axons.

This article has been cited by other articles:

				H.-L. Li, D. Hadid, and D. S. Ragsdale The Batrachotoxin Receptor on the Voltage-Gated Sodium Channel is Guarded by the Channel Activation Gate Mol. Pharmacol., April 1, 2002; 61(4): 905 - 912. [Abstract] [Full Text] [PDF]

				R. F. Rakowski, D. C. Gadsby, and P. De Weer Single Ion Occupancy and Steady-state Gating of Na Channels in Squid Giant Axon J. Gen. Physiol., February 22, 2002; 119(3): 235 - 250. [Abstract] [Full Text] [PDF]

				J. C. McPhee, D. S. Ragsdale, T. Scheuer, and W. A. Catterall A Critical Role for Transmembrane Segment IVS6 of the Sodium Channel [IMAGE] Subunit in Fast Inactivation J. Biol. Chem., May 19, 1995; 270(20): 12025 - 12034. [Abstract] [Full Text] [PDF]