Summating Potential of the Cochlea in the Guinea Pig

Abstract

The cochlear microphonics and the summating potential were recorded simultaneously by means of a superfine micropipette which was introduced into scala media through the round window. A sudden jump in dc resting potential from negative to positive occurred as the tip of the electrode penetrated the reticular lamina. At this instant a reversal in polarity of the summating potential and the cochlear microphonics was observed. The polarity and amplitude of the summating potential to long-lasting pure tones were dependent not only on intensity and frequency of stimuli but also upon the position of the recording electrode along the cochlea. A dc polarizing current was applied between scala vestibuli and scala tympani in the basal turn. Although both the positive and negative summating potentials were usually enhanced by dc current traveling from scala vestibuli to scala tympani and depressed by the dc current in the opposite direction, there were several exceptions. This fact suggests that the hair-bearing surface of the hair cells becomes unstable when the intracellular potential is changed markedly. Inconsistency of the summating potential with respect to both magnitude and polarity may be due to the instability of the hair cells that are exposed to a high potassium environment and a continuous anodal polarization in the form of the endocochlear potential.