Electrochemical profile for potassium ions across the cochlear hair cell membranes of normal and noise-exposed guinea pigs.

The electrochemical driving force for movement of potassium ions across the hair cell membranes was determined in normal and noise-exposed guinea pigs. The measurement of the electrical potential and the potentiometric determination of K+ activity difference across the cell membranes were accomplished with double-barreled K+-selective liquid membrane microelectrodes. Identification of hair cells was based on the sudden increase of the a.c. component of the receptor potential associated with the appearance of the membrane potential and an increase in K+ activity. The results suggest that K+ ions in the hair cell interior and the extracellular space of the organ of Corti are near electrochemical equilibrium. However, the electrochemical gradient for K+ between the hair cell interior and the subtectorial endolymph was very high. These findings imply that the resting potential of hair cells is mainly generated by the diffusion of K+ across the basolateral hair cell membrane and is not affected by contact of the apical cell membrane with K+-rich endolymph. Although cochlear microphonics recorded extracellularly were severely suppressed in guinea pigs exposed to broadband noise at 115 dBA for 7 days, the electrochemical profile for K+ across cell membranes of surviving hair cells did not show marked changes. The ratio of intracellular a.c. receptor potential to extracellular cochlear microphonics was much greater in surviving hair cells of noise-exposed guinea pigs.