NaK-ATPase in rat pancreatic islets.

Shifts in the distribution of the monovalent cations Na+ and K+ between the extra- and intracellular space seem to be important for the secretory response of the beta-cell. An attempt was therefore made to study the enzyme responsible for monovalent cation transport, the (NaK)-activated ATPase. In the presence of NaN3 as inhibitor of the mitochondrial Mg-ATPase, a NaK-ATPase with a specific activity of 72 mU X mg protein-1 could be demonstrated in crude membrane preparations of rat pancreatic islets. The enzyme, which was inactive in the absence of Mg++, needed both Na+ and K+ for activation and was inhibited by ouabain and PCMB. The main part of the NaK-ATPase was localized in the microsomal fraction. Glucose, sulphonylureas, somatostatin and diazoxide were without effect on NaK-ATPase.