title: Inhibition by glucagon of the calcium pump in liver plasma membranes.
abstract: The ATP-dependent calcium transport in plasma membrane vesicles prepared from rat liver was inhibited by 0.1 to 10 microM glucagon. Inhibition of the high affinity (Ca2+-Mg2+)-ATPase was observed concomitantly. This effect was neither mimicked by cyclic AMP nor by dibutyryl cyclic AMP. A study of the structure-activity relationships of six glucagon derivatives demonstrated the specificity of glucagon action since only one or two analogs markedly altered the (Ca2+-Mg2+)-ATPase activity. The study also demonstrated the total absence of correlation between adenylate cyclase activation and (Ca2+-Mg2+)-ATPase inhibition induced by these glucagon derivatives. The decrease in the maximal velocities induced by glucagon of both calcium transport and (Ca2+-Mg2+)-ATPase activity were related to a reduction in the rate of dephosphorylation of the Ca-dependent phosphorylated intermediate of the enzyme. This phosphorylated intermediate was characterized as a 32P-labeled 110,000-dalton protein which accumulated to 50 to 150% over the basal level in the presence of glucagon. The present results demonstrate a novel aspect of the role of glucagon as a calcium-mobilizing agent.
mesh_terms: D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D017301:Ca(2+) Mg(2+)-ATPase; D002118:Calcium / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors* / Q000302:isolation & purification; D002462:Cell Membrane / Q000201:enzymology; D005260:Female; D005934:Glucagon / Q000031:analogs & derivatives / Q000494:pharmacology*; D019811:Hydroxylamine; D006898:Hydroxylamines / Q000494:pharmacology; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008970:Molecular Weight; D051381:Rats; D011919:Rats, Inbred Strains; D013329:Structure-Activity Relationship
chemical_list: D006898:Hydroxylamines; D019811:Hydroxylamine; D003994:Bucladesine; D005934:Glucagon; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; D002118:Calcium