EFFECTS OF CLOFILIUM, A K CHANNEL BLOCKER, ON ELECTROGENIC K SECRETION AND AFFERENT DISCHARGE AT THE FROG SEMICIRCULAR CANAL - A PRELIMINARY-REPORT

Application of clofilium to the endolymphatic side of the isolated fro g semicircular canal abolished the transepithelial potential and produ ced increased K and mannitol outfluxes from the lumen to the dark cell s or the basolateral perilymph, with no apparent effect on active K se cretion. These results suggest an increased permeability of the parace llular pathway. When applied to the perilymphatic side in the intact l abyrinth, clofilium reduced the rates of quantal transmitter release ( miniature EPSP frequency), an effect that might arise from a decrease in the transduction current intensity secondary to the reduced transep ithelial electrochemical potential for K+. Moreover, afferent spike ra tes were almost completely abolished at rest as well as during mechani cal stimulation. This effect together with a decreased mEPSP amplitude points to a further direct action of clofilium on the afferent postsy naptic terminal. These results suggest a multi-factorial effect of clo filium that would reduce the sensitivity of the vestibular function.