Differences between the negatively activating potassium conductances of mammalian cochlear and vestibular hair cells

Abstract

Cochlear and type I vestibular hair cells of mammals express negatively activating potassium (K+) conductances, called gK,n and gK,L respectively, which are important in setting the hair cells' resting potentials and input conductances. It has been suggested that the channels underlying both conductances include KCNQ4 subunits from the KCNQ family of K+ channels. In whole-cell recordings from rat hair cells, we found substantial differences between gK,n and gK,L in voltage dependence, kinetics, ionic permeability, and stability during whole-cell recording. Relative to gK,L, gK,n had a significantly broader and more negative voltage range of activation and activated with less delay and faster principal time constants over the negative part of the activation range. Deactivation of gK,n had an unusual sigmoidal time course, while gK,L deactivated with a double-exponential decay. gK,L, but not gK,n, had appreciable permeability to Cs+. Unlike gK,L, g K,n's properties did not change ("wash out") during the replacement of cytoplasmic solution with pipette solution during ruptured-patch recordings. These differences in the functional expression of gK,n and gK,L channels suggest that there are substantial differences in their molecular structure as well.