Ultracytochemical demonstration of Ouabain-sensitive, K+-dependent P-nitrophenylphosphatase (NA+-K+-ATPase) activity in the rat hippocampal formation

The localization of ouabain-sensitive, K+-dependent p-nitrophenylphosphatase (K+-NPPase) activity, a part of the reaction of the Na+-K+-ATPase complex, was ultracytochemically investigated in the rat hippocampal formation called substantia gelatinosa cerebri. Microslicer sections of the hippocampal formation fixed with a mixture of 0.25% glutaraldehyde and 1% paraformaldehyde for 30 min were incubated in the medium for K+-NPPase.In the light microscopic observations, the most abundant reaction products were present in the stratum moleculare of the hippocampal formation. Electron microscopically, K+-NPPase activity was demonstrated on the axolemma, neurofilamentous structures in the axoplasm and synaptic plasma membrane. These activities were distinctly decreased with addition of 10 mM ouabain or substitution of Na+ for K+. Additionally, ouabain-insensitive, K+-independent p-NPPase activity was observed on the mitochondria, nuclear envelope and endoplasmic reticulum. Neurotubules did not show any K+-NPPase activity.