CYTOCHEMICAL-LOCALIZATION OF ADENYLATE-CYCLASE IN THE SODIUM-TRANSPORTING EPITHELIUM ISOLATED FROM FROG-SKIN

A modified cytochemical technique with 5'-adenylylimidodiphosphate as substrate, was used to examine the distribution of adenylate cyclase i n cells comprising the transepithelial Na+ transport pathway in isolat ed frog skin epithelium. particular attention was paid to the effects of fixation on the activity and localization of adenylate cyclase. Fix ation in glutaraldehyde alone or in combination with paraformaldehyde reduced the amount of reaction product, while better results were obta ined using unfixed tissues. Optimum results were obtained following st imulation of adenylate cyclase with forskolin and in the presence of s pecific metabolic inhibitors. Adenylate cyclase was localized in the b asolateral membranes of the principal cells which constitute a functio nal syncytium for Na+ transport and was absent from the apical membran es of the outermost granulosum cells. This distribution is consistent with the transepithelial Na+ transport model and defines the functiona l morphology of the cells involved in Na+ transport across hog skin. T he results are compatible with the process of Na+ re-absorption across other epithelial cells, verifying that frog skin is a convenient mode l-tissue to study Na+ transport mechanisms. Adenylate cyclase was also found in membranes of the mitochondria-rich cells, a minor and parall el Na+ transporting pathway.