PROTEIN-KINASE AND PROTEIN PHOSPHATASE PRESENCE IN THE STRIA VASCULARIS

Na+, K+-ATPase contributes to the high potassium concentration in the endolymph and the resulting endocochlear potential, which are both ess ential for the function of the sensory part of the inner ear. Na+, K+- ATPase is present in the stria vascularis and it has lately been sugge sted that its activity is hormonally regulated. The intracellular sign alling system for hormonal short-term regulation of Na+, K+-ATPase act ivity by phosphorylation in renal tubular cells has been well describe d. In this study, the presence of the intracellular components of this phosphorylation system in the stria vascularis from guinea-pig has be en investigated with immunoblotting. The concentrations found were rel ated to those in renal medullary tissue or the corpus striatum. Protei n kinase C was present with isoforms alpha, delta and zeta in the stri a vascularis. Calcium- and calmodulin-dependent protein kinase II and protein phosphatase-1 isoforms alpha and gamma were found in the stria vascularis. Protein phosphatase-2B, on the other hand, could not be d etected. I-1, an inhibitor of protein phosphatase activity, was presen t, whereas the phosphatase inhibitor dopamine- and cAMP-regulated phos phoprotein (DARPP-32), was not present in the stria vascularis. These results demonstrate that several intracellular components of the phosp horylation/dephosphorylation system are present in the stria vasculari s, and suggest that hormonal short-term regulation of Na+, K+-ATPase a ctivity is also possible in the stria vascularis.