Action potential of isolated frog utricle.

The action potential of an isolated frog utricle was recorded using a suction electrode. The utricle was stimulated with iron sand which were spread evenly on the macula. A magnetic force was employed to induce the iron sand to depress the macula lightly. Integration of the action potential resulted in a phasic component, just as observed in the isolated semicircular canal potential (Harada et al., 1969). The amplitude of the utricular phasic component was liner to the logarithm of the stimulus intensity. Similar relationship was observed between the semicircular canal action potential and the stimulus (Harada & Hirata, 1981). Phasic on-response was invariably accompanied by an off-response. This suggests functional polarization of the utricle. It is already known that the macula is divided by the striola into two hair-cell groups having differing polarity. Since iron sand is spread evenly on the macula, all sensory cilia bend in one direction at the onset of the stimulus and one of the two cell groups evokes an on-response. At termination of the stimulus, sensory cells with the opposite polarity are stimulated, thus producing an off-response.