The Journal of General Physiology
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Published 1 March 2000. doi:10.1085/jgp.115.3.257
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© The Rockefeller University Press, 0022-1295/2000//257/ $5.00
Journal of General Physiology, Volume 115, Number 3, 2000

Original Article

Independence and Cooperativity in Rearrangements of a Potassium Channel Voltage Sensor Revealed by Single Subunit Fluorescence

Lidia M. Mannuzzua and Ehud Y. Isacoffa

a From the Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, California 94720-3200
Department of Molecular & Cell Biology, University of California, Berkeley, 271 Life Sciences Addition, Berkeley, CA 94720-3200.510-643-6791

eisacoff{at}socrates.berkeley.edu

Voltage-gated potassium channels are composed of four subunits. Voltage-dependent activation of these channels consists of a depolarization-triggered series of charge-carrying steps that occur in each subunit. These major charge-carrying steps are followed by cooperative step(s) that lead to channel opening. Unlike the late cooperative steps, the major charge-carrying steps have been proposed to occur independently in each of the channel subunits. In this paper, we examine this further. We showed earlier that the two major charge-carrying steps are associated with two sequential outward transmembrane movements of the charged S4 segment. We now use voltage clamp fluorometry to monitor these S4 movements in individual subunits of heterotetrameric channels. In this way, we estimate the influence of one subunit's S4 movement on another's when the energetics of their transmembrane movements differ. Our results show that the first S4 movement occurs independently in each subunit, while the second occurs cooperatively. At least part of the cooperativity appears to be intrinsic to the second S4 charge-carrying rearrangement. Such cooperativity in gating of voltage-dependent channels has great physiological relevance since it can affect both action potential threshold and rate of propagation.

Key Words: potassium channel • cooperativity • fluorescence • voltage-sensing • gating

© 2000 The Rockefeller University Press


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[Abstract] [Full Text] [PDF]


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