Biophysical Journal 72: 188-192 (1997)
© 1997 the Biophysical Society

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Ion conductance of the Ca(2+)-activated maxi-K+ channel from the embryonic rat brain.

Laboratory of Neurophysiology, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892, USA. jmm@psych.uic.edu

ABSTRACT

By using single-channel recording techniques, we measured the conductance (gK) of the Ca(2+)-activated Maxi-K+ channel from the embryonic rat brain, and examined its dependence on K+ ions present in equimolar concentrations on both sides of the membrane patch. With ionic strength maintained constant by substitution of N-methyl-D-glucamine for K+, gK has a sigmoidal dependence upon [K+]. This result has been obscured in previous work by variations in ionic strength, which has a marked effect on single-channel conductance, especially in the limit for which this variable approaches zero. The gK versus [K+] relationship is described, theoretically, by a three-barrier, two-binding-site model in which the barrier that an ion must cross to leave the channel is decreased as [K+] is increased.

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