Demonstration of adenylate cyclase activity in stria vascularis of guinea pig cochlea

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Cholera toxin-stimulated adenylate cyclase activity was demonstrated cytochemically in the stria vascularis of the guinea pig inner ear by the cerium method of Rechardt and Hervonen, and it was compared with ALPase, Mg-ATPase, Ca-ATPase and Na, K-ATPase activity. Adenylate cyclase activity was observed in the marginal and basal cells. The reaction products were fine granular particles on the plasma membrane of the basal infoldings of the marginal cells, but not on that of the free surface facing the endolymphatic space. Enzyme activity was also observed in the large mitochondria;the reaction was intense in the outer chamber and weak in the cristae, was inhibited by 5 mM alloxan. The plasma membranes of adjacent basal cells showed a positive rea-ction. No enzyme activity was detected in the intermediate cells, the endothelial cells of the capillaries in the stria vascularis, fibrocytes in the spiral ligament, epithelial cells of the spiral prominence, Corti's organ or Reissner's membrane. In the marginal cells, the location of adenylate cyclase activity corresponded with that of Na, K-ATPase activity. Therefore, the adenylate cyclase activity of the stria vascularis may play a role in the regulation of the membrane permea-bility to water and electrolytes while Na, K-ATP-ase acts as an ion pump to maintain high potassium and low sodium ion concentrations in the endolymph.
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