TETRAETHYLAMMONIUM EFFECTS ON COCHLEAR POTENTIALS IN THE GUINEA-PIG

Voltage-dependent K+ channels in the basolateral membrane of hair cell s in guinea-pig cochlea might contribute to the non-linear current-vol tage relationships in these hair cells and, thereby, to generation of the extracellular summating potential (SP). To evaluate the role of K channels in the generation of the SP the perilymphatic perfusion tech nique was used to introduce the K+-channel blocker tetraethylammonium (TEA) into the cochlea. Sound-evoked cochlear potentials were measured subsequently. Without blocking nerve activity TEA induced reversible shifts of the SP in the negative direction, irrespective of whether we recorded from scala vestibuli or scala tympani. Shifts in the negativ e direction were probably due to TEA acting directly on the afferent f ibres, since removal of nerve activity by the potent Na+-channel block er tetrodotoxin (TTX) prevented TEA from shifting the SP in the negati ve direction. Once nerve activity had been removed by TTX, administrat ion of TEA caused a small decrease in the magnitude of the SP, both in scala vestibuli and in scala tympani, irrespective of its polarity. T he decrease was significant for the highest test frequencies only (8-1 2 kHz), and completely reversible. The rapidly activated K+ channel in the inner hair cell (IHC) is probably blocked by TEA and this blockin g might be responsible for the small decrease in magnitude of the SP. The asymmetric contribution from this K+ channel to the IHC's current- voltage relationship seems to be only partly responsible for the gener ation of the SP, since blocking of this K+ channel with TEA caused rel atively small decreases in the amplitude of the SP. TEA did not affect the endocochlear potential.