Response of cochlear potentials to presumed alterations of ionic conductance: endolymphatic perfusion of barium, valinomycin and nystatin.

Two models ('single-pump' and 'two-pump') of transepithelial potassium movement by the marginal cells of the stria vascularis have been proposed in the literature. Their validity was considered by exposing the endolymphatic (luminal) surface to agents (barium, valinomycin and nystatin) which are known to alter specific cellular membrane conductances in other tissues. This was accomplished by the use either of injections or of a relatively satisfactory technique for perfusion of scala media, which is described. Injection of barium caused the endocochlear potential (EP) to increase in normal animals and had no effect on the EP of deaf, Waltzing guinea pigs. Perfusion of the ionophores caused a decline in the EP in both normal and Waltzing guinea pigs. Only the 'two-pump' model (Na/K-ATPase-mediated cation pump on the basolateral membrane and rheogenic K transporter at the luminal membrane) is consistent with the results. The cellular heterogeneity of the cochlear duct, however, introduces a measure of uncertainty into this interpretation.