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(Hypertension. 1995;25:365-371.)
© 1995 American Heart Association, Inc.

Articles

Modulation of the Ca²⁺ Pump by the Hypothalamic-Hypophysary Inhibitory Factor

Mercedes Ricote; Elena García-Martín; Jose Sancho; Carlos Gutiérrez-Merino

From Serv. Endocrinología, Hospital Ramón y Cajal, Madrid (M.R., J.S.), and the Departamento de Bioquímica y Biología Molecular y Genética, Facultad de Ciencias Badajoz (E.G.-M., C.G.-M.), Spain.

Abstract We previously purified to homogeneity an endogenous sodium pump inhibitor from bovine hypothalamus and hypophysis that is different from digoxin or ouabain and studied the effects of this factor on the total Ca²⁺,Mg²⁺-ATPase activity of plasma membrane of synaptosomes. This factor inhibits the calcium pump and the total Mg²⁺-ATPase activity of these membranes with approximately the same K_0.5 values of inhibition. The potency of this factor as an inhibitor depends on the membrane concentration in the assay medium. The inhibition of the magnesium-dependent ATPase activities of these membranes was of a noncompetitive type with respect to the substrate Mg²⁺-ATP and did not significantly shift the calcium dependence of the Ca²⁺,Mg²⁺-ATPase activity. We suggest that the calcium pump of the synaptosomal plasma membrane is inhibited by this factor through disruption of the lipid annulus; this inhibition could play a role in the control of calcium homeostasis by increasing the cytosolic free calcium concentration.

Key Words: calcium pump • Na⁺,K⁺-transporting ATPase • Ca²⁺-transporting ATPase • sodium-potassium pump • inhibitor

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