Nimodipine, an L-channel Ca 2+ antagonist, reverses the negative summating potential recorded from the guinea pig cochlea

Abstract

Nimodipine, an L-type Ca 2+ channel antagonist, was tested using sound-evoked cochlear potentials in guinea pigs to investigate whether these channels are involved in cochlear function. Perilymph spaces of guinea pig cochleae were perfused with artificial perilymph solutions containing 0.1–10 μM nimodipine at a rate of 2.5 μl/min for 10 min. The cochlear potentials evoked by 10 kHz tone bursts of varying intensities were recorded from the basal turn of the scala vestibuli. Cochlear perfusion of nimodipine resulted in reversible, dose-related suppression of the compound action potential of the auditory nerve (CAP; N 1-P 1), a prolongation of N 1 latency at suprathreshold levels, an elevated CAP threshold, a decrease in N 1 latency at a constant amplitude measured at CAP threshold, a reduction in cochlear microphonics (CM), and a reduction of the negative summating potential (SP) to a point where it became positive (i.e., a reversal of SP). The endocochlear potential (EP) was not affected. These results support the hypothesis that L-type Ca 2+ channels are directly involved in the operation of the organ of Corti. We speculate that L-type Ca 2+ channels are integrally involved in generation of a negative summating potential and the dc motion of the cochlear partition described by others.