A Ca2+-activated K+ channel from rabbit aorta: modulation by cromakalim

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Abstract

A large conductance Ca2+-activated K+ channel from rabbit aorta was incorporated into planar lipid bilayers. This channel had a conductance of 337 ± 7 pS in symmetrical 250 mM KCl solutions and had a Na+/K+ permeability ratio of < 0.04. In asymmetrical solutions containing 300 mM KCl cis (intracellular), 100 mM KCl trans (extracellular) or 100 mM KCl cis 500 mM KCl trans, the reversal potentials for the channel were −30 and +46 mV, respectively. This channel possessed voltage-dependent activation and cis (intracellular) Ca2+ sensitivity. Cromakalim (50 nM) added to the trans side of the bilayer significantly increased the Popen by 56% from 0.09 ± 0.01 to 0.14 ± 0.01(P < 0.01) at −40 mV without altering the single channel conductance. This effect was dose-dependent, increasing at higher cromakalim concentrations. The primary effect of cromakalim was to decrease the τslow of the channel closed state from 266 ± 32 to 147 ± 17 ms which is sufficient to account for the increase in Popen of the channel in the presence of cromakalim.

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