Effects of epinephrine on ouabain-sensitive, K+-dependent p-nitrophenylphosphatase activity in strial marginal cells of guinea pigs

In strial marginal cells, Na+/K+-ATPase activity is abundant, and contribut es to maintain the characteristic electrolyte composition of the cochlear e ndolymph. In the present study, to clarify the relationship between epineph rine 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 p igs treated with reserpine, epinephrine, and reserpine plus epinephrine. In our previous study, K+-NPPase activity had almost completely decreased 3 t o 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 w as able to restore strial K+-NPPase activity in the reserpine-treated anima ls, and that epinephrine might increase strial Na+/K+-ATPase activity.