The generation of DC potentials in a computational model of the organ of Corti: effects of voltage-dependent K+ channels in the basolateral membrane of the inner hair cell.

A computational model of the organ of Corti is described to assist in the interpretation of electrophysiological data concerning the role of the K+ channels residing in the basolateral membrane of cochlear hair cells. Recent in vivo data from Van Emst et al. (Hear. Res. 88, 27-35 (1995); Hear. Res. 102, 70-80 (1996)) about the effects of selective blocking of K+ channels indicate that these channels affect the magnitude of the summating potential. In order to understand the nature of this effect, the model of Dallos (Hear. Res. 14, 281-291 (1984)) was extended to account for the voltage- and time-dependent properties of the K+ channels in the basolateral membrane of the inner hair cell (IHC) (Kros and Crawford, J. Physiol. 421, 262-291 (1990)). The model shows that the K+ channels induce a shift in the mean IHC basolateral conductance when high-frequency stimuli are present. As a result, cochlear transduction shifts to a different electrical operating state and this is the source of a marked decrease in the stimulus-evoked DC response of the IHC. Extracellularly, in contrast, the magnitude of the DC response increases slightly. At low frequencies, the K+ channels respond to the stimulus waveform on a cycle-by-cycle basis. The waveform distortion associated with this dynamic basolateral impedance induces a further decrease in the intracellular stimulus-evoked DC response of the IHC. Thus, K+ channels in the IHC appear to be directly involved in the generation of the DC receptor potential at low frequencies, but at high frequencies they simply modify the size of the DC response.