Action of Energy-rich Phosphate Compounds on Cochlear Potentials

Abstract

Endocochlear potential (EP), cochlear microphonics (CM), and action potentials N1 were recorded from the basal turn of the guinea pig's cochlea to which various energy-rich phosphate (∼P) compounds and metabolic inhibitors were applied by microinjection and ionophoretic techniques. The administration of some ∼P compounds, such as adenosine triphosphate, into the scala media produced a prompt depression, followed by recovery, and then a gradual decrease in the cochlear potentials. The EP dropped to 30.9% to 60.5% of the original level within 2 min after injection of adenosine triphosphate and returned to 75.5% to 100%. Other substances, similar in structure or in charge to ∼P compounds, were tested for their effects. In another group of experiments, anoxia brought about the usual reduction in cochlear potentials during and after the application of ∼P compounds. The metabolic inhibitors that block adenosine triphosphate production and utilization acted as a depressant on these potentials. A possible rôle of metabolic energy in maintaining oxygen-sensitive cochlear potentials is discussed, and the prompt depression of EP induced by ∼P compounds is analyzed.