Carbonic anhydrase activity in the inner ear.

The histochemical and cytochemical localization of carbonic anhydrase activity in the inner ear of guinea pig was studied with Hansson's method and modified Yokota's method. All cells possessing the cell membrane infoldings are proved to have the enzymatic activity. The cochlear hair cells show strong enzymatic activity while the vestibular hair cells show no appreciable activity. The supporting cells of both cochlear and vestibular hair cells also show the enzymatic activity. The reaction products showing the enzymatic activity are observed in the cytoplasm, nucleus and cell membrane of the stained cells with both light microscope and electron microscope. The stria vascularis, vestibular dark cells and endolymphatic sac are proved to have the enzymatic activity. The cells, which are already proved to have Na+-K+-ATPase activity, show the enzymatic activity. The regulation of the fluid and ion in the inner ear is probably a complex mechanism involving not only various cells but also several enzymes such as carbonic anhydrase, Na+-K+-ATPase and adenylate cyclase.