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 essential 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 suggested that its activity is hormonally regulated. The intracellular signalling system for hormonal short-term regulation of Na+, K+-ATPase activity by phosphorylation in renal tubular cells has been well described. In this study, the presence of the intracellular components of this phosphorylation system in the stria vascularis from guinea-pig has been investigated with immunoblotting. The concentrations found were related to those in renal medullary tissue or the corpus striatum. Protein kinase C was present with isoforms alpha, delta and zeta in the stria 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 detected. I-1, an inhibitor of protein phosphatase activity, was present, whereas the phosphatase inhibitor dopamine- and cAMP-regulated phosphoprotein (DARPP-32), was not present in the stria vascularis. These results demonstrate that several intracellular components of the phosphorylation/dephosphorylation system are present in the stria vascularis, and suggest that hormonal short-term regulation of Na+, K+-ATPase activity is also possible in the stria vascularis.