Effects of Epinephrine on Ouabain-Sensitive, K+-Dependent P-Nitrophenylphosphatase Activity in Strial Marginal Cells of Guinea Pigs

Abstract

In strial marginal cells, Na+/K+-ATPase activity is abundant, and contributes to maintain the characteristic electrolyte composition of the cochlear endolymph. In the present study, to clarify the relationship between epinephrine and strial Na+/K+-ATPase activity, the ouabain-sensitive, K+-dependent p-nitrophenylphosphatase (K+-NPPase) activity of strial marginal cells was investigated with a cerium-based method in normal guinea pigs and guinea pigs treated with reserpine, epinephrine, and reserpine plus epinephrine. In our previous study, K+-NPPase activity had almost completely decreased 3 to 20 days after reserpine administration. In the present study, at 10 days after reserpinization and following repeated epinephrine treatment, enzyme activity was detectable. These results suggest that exogenous epinephrine was able to restore strial K+-NPPase activity in the reserpine-treated animals, and that epinephrine might increase strial Na+/K+-ATPase activity.