Ionic properties of IK,n in outer hair cells of guinea pig cochlea

The ionic properties of voltage-dependent K+ current activated at the resting membrane potential (IK,n) of outer hair cells (OHC) isolated from the guinea pig cochlea were studied using a patch-clamp technique in a whole-cell recording mode. The reversal potential of IK,n indicated a high selectivity for K+, and the relative permeability ratios for various monovalent cations were K+:Rb+:NH4+ = 1:1.21:0.13. Decrease in extracellular Cl- inhibited the IK,n. IK,n was blocked by Cs+ and Ba2+, although the inhibitory manner of Cs+ and Ba2+ were voltage-dependent and voltage-independent, respectively. By the use of puff-application method, the local application of Ba2+ to basolateral surface of OHC shifted the holding current level in an inward direction, whereas the application to apex and hair showed little change. Indicating that the IK,n channels preferentially locate at the basolateral region of cell membrane.