EXTERNAL PH REGULATES THE SLOWLY ACTIVATING POTASSIUM CURRENT I(SK) EXPRESSED IN XENOPUS OOCYTES

A slowly activating, delayed rectifier potassium current, I(sK), was expressed in Xenopus laevis oocytes by injection of cRNA transcribed from a rat kidney cDNA clone. External acidification reversibly decreased the current amplitude. The effects were concentration dependent on protons with K(d) at pH almost-equal-to 5.5 and a Hill coefficient of 1.0. External acidification reduced the maximal conductance (G(max)) without affecting the activation kinetics; this effect was not dependent on membrane voltages. These data suggest that H+ ions bind to the channel with a one-to-one stoichiometry, and this binding site may be located outside of the membrane electric field.