Traveling Wave—Source of Negative Summating Potentials

Abstract

Cochlear microphonics (CMs), summating potentials (SPs), endocochlear potentials (EPs), and potassium concentration (K+) have been recorded from the guinea pig's cochlea. Standard glass microelectrodes and microelectrodes sensitive for K+ have been introduced into the scala media. In the first part of the experiments, potentials were measured under different sound pressure levels (SPLs)—80, 90, and 100 dB at I, II, and III turns. In the second part of the experiments, changes in K+ concentration, SP, CM, and EP (following anoxia and perfusion of the scala tympani by Ringer's solution, ethacrynic acid, and artificial endolymph) were recorded. Maximum negative summating potentials with their increasing SPL were recorded in loci appropriate for the analysis of those frequencies. Continuous changes in potentials and K+ concentration are produced by anoxia and by ethacrynic acid in the scala tympani. In both experiments, when active ion transport is paralyzed, the concentration of K+ in in the scala media and the negativity of SP falls. Replacement of perilymph in the scala tympani by a solution with the same concentration of K+ as endolymph immediately produces a rapid increase of K+ concentration inside the scala media and at the same time an increase in the negative SP. [Supported by NIH grant.]