[Effects of some bivalent and trivalent ions and of EGTA on the process of activation of the ampullar receptors].

In order to define the role of Ca++ in labyrinthine receptors the endolymph in isolated canal preparations was replaced with modified solutions containing Ca-substitutes(Sr++, Ba++), Ca-antagonists(La+++, Cd++, Mg++) and Ca-chelating agents(EGTA). The response of the receptors was evaluated by recording the slow and propagated potentials from the ampullar nerve. All the tested solutions proved able to depress or cancel the mechanically evoked responses of ampullar receptors. The presence of Ca++ in the endolymph is therefore essential to grant the mechanosensitivity of the hair cells. The receptor blockade produced by Ca-withdrawal develops much earlier under continuous mechanical stimulation. This suggests that Ca++ might be bound in some structures and released during cupula deflections.