Cytochemical study of ouabain-sensitive, K(+)-dependent p-nitrophenylphosphatase activity in guinea pig facial nerve

The localization of ouabain-sensitive, K(+)-dependent p-nitrophenylphosphatase (K-NPPase) activity, the second dephosphorylative property of the Na-K adenosine triphosphatase complex, was cytochemically studied in the intra-temporal portion of the facial nerve in normal guinea pigs using a cerium-based method. A fine-granular reaction product of the K-NPPase activity was observed on the cytoplasmic side of the axolemma of the axon cylinder, of the incisures of Schmidt-Lanterman, and of the nodes of Ranvier. No reaction product was detected on the periaxonal and outermost plasma membrane of Schwann cells and in the myelin sheath. In control tissue samples, the enzyme activity was almost completely inhibited by 10 mM ouabain, and no reaction was noted in medium without K+.