Cytochemical localization of K+-dependent p-nitrophenyl phosphatase and adenylate cyclase by using one-step method in human washed platelets

Summary Ultrastructural cytochemical localization of ouabain-sensitive, potassium dependent p-nitrophenyl phosphatase (K⁺-NPPase) of the Na⁺-/K⁺-ATPase complex and adenylate cyclase (cAMPase) activities, in washed inactivated human platelets, are described. The one-step lead-citrate method, under similar incubation conditions, was used to determine both activities. K⁺-NPPase appeared in both plasma membrane and the surface-connected canalicular system (SCCS) of the platelets. These data suggest a uniform distribution of the enzyme throughout membrane systems which are in contact with the external medium. cAMPase activity was strictly localized in tubules of the dense tubular system (DTS) when incubation medium contained prostaglandin E₁, prostaglandin D₂ or forskolin, at concentrations known to stimulate the enzyme in platelets that are intact. This fact and the inhibition of cytochemical reaction by thrombin confirm that the one-step lead-citrate method is a useful procedure in determining adenylate cyclase, abolishing the unfavorable conditions of previously reported methods.