Carbonic anhydrase activity in stria vascularis and dark cells in vestibular labyrinth

Carbonic anhydrase activity was demonstrated ultracytochemically in the dark cells of the vestibular labyrinth and in the stria vascularis of the guinea pig. Reaction products were found both in the dark cells and in the stria vascularis. Localization of carbonic anhydrase was very similar between the dark cells and the intermediate cells, but the marginal cells had a different localization pattern. In both the dark cells and the intermediate cells, the reaction products were deposited in the cytoplasm, especially in the infoldings. In the marginal cells, carbonic anhydrase activity was observed on the lateral plasma membrane of the apical area and in a few apical vesicles, but was not detected in the infoldings of the deep portion. Reaction products were also observed in the intercellular spaces between the marginal cells. No reaction products were observed in the basal cells and transition cells. Carbonic anhydrase activity was observed in the cytoplasm of capillary endothelial cells and the fibrocytes of the spiral ligament. It is considered that carbonic anhydrase may play a major role in water and electrolyte transport in both the dark cells and stria vascularis.