Exploration of Cochlear Potentials in Guinea Pig with a Microelectrode

The ac (“microphonic”) cochlear potential and the positive dc “endolymphatic” potential have been recorded simultaneously as the exploring electrode was introduced into scala media or as other parameters were varied. Negative intracellular de potentials were demonstrated in the cells of the organ of Corti. The zone of positive endolymphatic potential is bounded by the reticular lamina, not by the basilar membrane. The cochlear microphonic reverses phase as the exploring electrode penetrates the reticular lamina. A dc polarizing current with the positive pole in scala media (and negative in scala tympani) increases the cochlear microphonic just as it does when the positive pole is located in the scala vestibuli. These facts indicate that the source of the ac (microphonic) potential seems clearly to be at the hair‐bearing end of the hair cells and that the source of the dc endolymphatic potential is probably here also, while Reissner's membrane is not the source of either the ac or the dc potential. No steady dc current flow outside scala media was found such as would be expected if stria vascularis were the dc source and if the hair cells modulated a dc current flow through them. The dc endolymphatic potential may be increased by as much as 10 percent if and while the basilar membrane is displaced toward scala vestibuli and may be decreased to 50 percent or less when and while it is displaced toward scala tympani. Isotonic solutions rich in potassium depressed the ac potential and nerve responses when introduced into scala tympani but not when in scala vestibuli only. The. dc potential, however, was not altered by high potassium concentration in scala tympani.