Pharmacological and kinetic analysis of K channel gating currents.
We have measured gating currents from the squid giant axon using solutions that preserve functional K channels and with experimental conditions that minimize Na channel contributions to these currents. Two pharmacological agents were used to identify a component of gating current that is associated with K channels. Low concentrations of internal Zn2+ that considerably slow K channel ionic currents with no effect on Na channel currents altered the component of gating current associated with K channels. At low concentrations (10-50 microM) the small, organic, dipolar molecule phloretin has several reported specific effects on K channels: it reduces K channel conductance, shifts the relationship between channel conductance and membrane voltage (Vm) to more positive potentials, and reduces the voltage dependence of the conductance-Vm relation. The K channel gating charge movements were altered in an analogous manner by 10 microM phloretin. We also measured the dominant time constants of the K channel ionic and gating currents. These time constants were similar over part of the accessible voltage range, but at potentials between -40 and 0 mV the gating current time constants were two to three times faster than the corresponding ionic current values. These features of K channel function can be reproduced by a simple kinetic model in which the channel is considered to consist of two, two-state, nonidentical subunits.
Spires
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Department of Physiology, University of Rochester School of Medicine and Dentistry, New York 14642.
Begenisich
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D000818:Animals; D001369:Axons / Q000378:metabolism; D049832:Decapodiformes; D004553:Electric Conductivity; D006706:Homeostasis; D007700:Kinetics; D010693:Phloretin / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D015222:Sodium Channels / Q000502:physiology; D015032:Zinc / Q000494:pharmacology
D015221:Potassium Channels; D015222:Sodium Channels; D015032:Zinc; D010693:Phloretin