Effects of calcium on sound-evoked cochlear potentials in the guinea pig.

Scala tympani in guinea pigs were perfused with artificial perilymph solutions containing calcium in ionic concentrations from 2.7 to 80 mEq/L. Cochlear‐potential responses to 7000‐cps tone pips at 80 dB re 0.0002 dyn/cm2 were recorded from the first turn using differential electrodes. The cochlear‐microphonic (CM) and negative summating‐potential (SP) amplitudes recovered immediately following perfusion and were augmented relative to control values for several minutes thereafter. The N1 component of the action potential (AP) recovered within 2 min or less after perfusion with solutions containing normal concentrations of calcium, but was depressed for longer periods with increasing concentrations. Depression of the AP was qualitatively related to the increase in calcium concentration. Augmentation of the CM and SP and depression of the AP associated with increased calcium concentrations in scala tympani are discussed in relation to the generation of these potentials and the action of the olivo‐cochlear b...