Phasic components of isolated frog utricle and the effect of ototoxic drugs

Abstract

The action potential of an isolated frog utricle was recorded using a suction electrode. The utricle was stimulated with iron sand which was spread evenly on the macula. A magneticforce was employed to induce the iron sand to depress the macula lightly. From this experiment, two kinds of action potentials were recorded from the utricular nerve. One was the phasic component with adaptation and the other was the tonic component without adaptation. The phasic component adapted in 5-8 seconds after the onset of the stimulus. When two stimuli were superimposed, amplitudes of the potential evoked by the second stimulus were almost the same, regardless of the timing of the second stimulus. In addition, the amplitudes of the potential evoked by the second stimulus varied exactly in accordance with the intensity of the second stimulus. These results indicated that the utricle has two kinds of receptors with different thresholds. Furthermore, it is suggested that receptors of the phasic components accurately monitor the changes of the stimulus intensity. Streptomycin (SM) or 3', 4'-dideoxykanamycin B (DKB) were added to the frog Ringer's solution in order to examine the effect of these drugs on the phasic component of the frog utricle. Action potential completely disappeared with the concentratin of 600γ/ml of SM and 300γ/ml of DKB. The ototoxicity of these drugs on the vestibular sensory cells possibly depends on the efficacy of the drug itself as well as on the affinity of the drug to the sensory cells.