ATP ANTAGONISTS CIBACRON BLUE, BASILEN BLUE AND SURAMIN ALTER SOUND-EVOKED RESPONSES OF THE COCHLEA AND AUDITORY-NERVE

The P-2-purinergic receptor antagonists suramin, cibacron blue and basilen blue, the latter two being isomers of reactive blue 2, were studied for their effects on sound-evoked responses from the cochlea (cochlear microphonic, CM; summating potential, SP; distortion product otoacoustic emissions, DPOAE) and auditory nerve (compound action potential, CAP). Local application of these compounds (10-1000 mu M) into the cochlear perilymph was associated with concentration-dependent response alterations. Effects of suramin on cochlear responses were minimal: High-intensity SP was reduced slightly at concentrations greater than or equal to 330 mu M without significant alterations in CM or DPOAEs. The amplitude of the auditory nerve CAP was suppressed and its latency increased at drug concentrations > 100 mu M, Cibacron blue and basilen blue were of greater potency in their effects on cochlear and auditory nerve responses. DPOAEs were generally reduced, low-intensity SP was reduced and high-intensity SP was increased and CM was little affected at drug concentrations 100-1000 mu M. The CAP was suppressed and its latency increased at concentrations 133 mu M. Effects of suramin were largely reversible; those associated with cibacron blue and basilen blue generally were not. To the extent that these drugs acted selectively as antagonists of ATP receptor-mediated activity, results support the hypothesis that endogenous ATP exerts profound actions at the level of the cochlea and the auditory nerve.