Ultracytochemical localization of Ca++-ATPase activity in pituicytes of the neurohypophysis of the guinea pig.
Ca++-ATPase activity (cf. Ando et al. 1981) was examined both light- and electron-microscopically in the neurohypophysis of the guinea pig. Apart from a strong activity within the walls of the blood vessels, in the parenchyma of the neurohypophysis the reaction product of the Ca++-ATPase activity was restricted to the plasmalemma of the pituicytes. This reaction was completely dependent upon Ca++ and the substrate, ATP; the reaction was inhibited by 0.1 mM quercetin, an inhibitor of Ca++-ATPase. A reduction of the enzyme activity occurred by 1) adding Mg++ to the standard incubation medium, and 2) substituting Ca++ with Mg++ at varying concentrations. In all experiments the neurosecretory fibers were devoid of Ca++-ATPase activity. The function of the Ca++-ATPase activity in the plasmalemma of the pituicytes is discussed in connection with the regulation of the extracellular Ca++ concentration, which seems to be important with respect to the discharge of secretory material from the neurosecretory fibers.
D000818:Animals; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D006168:Guinea Pigs; D006651:Histocytochemistry; D008297:Male; D008854:Microscopy, Electron; D010904:Pituitary Gland, Posterior / Q000166:cytology / Q000201:enzymology* / Q000648:ultrastructure
D000252:Calcium-Transporting ATPases