Studies on (Na +-K +)-activated ATPase XXIV. Localization and properties of ATPase in the inner ear of the guinea pig

Abstract

1. (1) The properties and distribution of an ouabain-sensitive (Na +-K +)-ATPase system in the inner ear structures of the guinea pig were investigated with ultramicrochemical techniques. The properties of this enzyme system are in good agreement with those found in other tissues. 2. (2) The enzyme was present in high activity in the stria vascularis (7.95 moles/kg dry wt. per h). There was a clear decrease in enzyme activity from the base of the cochlea to the apex. 3. (3) The enzyme activity in the other cochlear structures was rather low (< 0.5 mole/kg dry wt. per h), with the exception of the highly vascularized part of the spiral ligament (1.60 mg moles/kg dry wt. per h). 4. (4) These results strongly suggest that the (Na +-K +)-ATPase system in the stria vascularis plays the primary role in the maintenance of the cochlear cation gradients, while the contribution of Reissner's membrane to this process can only be very minor. 5. (5) The good agreement between the half maximal inhibition concentration of ouabain for the enzyme system and the cochlear potentials, indicates moreover, a dependence of these potentials on the functioning of the (Na +-K +)-ATPase system.