pH modulates the vestibular afferent discharge and its response to excitatory amino acids

In the isolated inner ear of the axolotl (Ambystoma tigrinum) acid pH decreased and basic pH increased the resting and mechanically evoked spike discharge of semicircular canal afferent neurons. Variations in pH also modified the afferent neuron response to N-methyl-D-aspartic acid (NMDA) acid and to (+/-)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA). Responses to both excitatory amino acid agonists increased at pH 7.8 (41% and 22%, respectively) and decreased by perfusion of the preparation with a saline solution, of pH 7.0 (28% in both cases). These results indicate that vestibular endorgans have a significant sensitivity to pH that could play a significant role in various pathological states, and may also contribute to the post-transductional processing of sensory information.