Transient expression of an inwardly rectifying potassium conductance in developing inner and outer hair cells along the mouse cochlea

Inwardly rectifying K+ currents in inner and outer hair cells (IHCs, OHCs) were studied during post natal development of the mouse cochlea. Hyperpolar izing steps: from a holding potential of -64 mV induced a rapidly activatin g current in both cell types. This current showed strong inward rectificati on around the Kt equilibrium potential and, at potentials negative to -130 mV, partial inactivation. The activation range varied with extracellular K concentration. External application of Ba2+ and Cs+ reversibly blocked the elicited current. The results are consistent with the presence of an I-K1- type inwardly rectifying potassium conductance in these cells. The maximum current was 60% larger in IHCs than in OHCs; In OHCs, but not IHCs, the amp litude of I-K1 varied significantly with the cells' position along the coch lea. I-K1 was maximal in cells located in the most basal region of the coch lea and its amplitude decreased in the apical coil. I-K1 disappeared upon f unctional maturation: in OHCs at the end of the first postnatal week, and i n IHCs at the onset of auditory function 12 days after birth. The current i s active at the resting potential of the cells and plays a role in regulati ng the spiking behaviour characteristic of developing hair cells.