title: Cholera toxin blocks glucagon-mediated inhibition of the liver plasma membrane (Ca2+-Mg2+)-ATPase.
abstract: We have previously shown that liver plasma membrane (Ca2+-Mg2+)-ATPase activity is inhibited by glucagon. To investigate the possible involvement of a GTP-binding (G) protein in this regulation, we have examined the effects of pertussis toxin and cholera toxin on inhibition of (Ca2+-Mg2+)-ATPase by glucagon. Treatment of liver plasma membranes with pertussis toxin did not affect the sensitivity of (Ca2+-Mg2+)-ATPase to the hormone. In contrast, treatment of plasma membranes or prior injection of animals with cholera toxin prevented inhibition of the (Ca2+-Mg2+)-ATPase by glucagon. Even though adenylate cyclase activity was increased by cholera toxin treatment, addition of cyclic AMP did not mimic the effect of cholera toxin in blocking glucagon-mediated inhibition of (Ca2+-Mg2+)-ATPase activity. These data suggest that a cholera toxin-sensitive protein, perhaps Gs or a Gs-like protein, is involved in the regulation of liver (Ca2+-Mg2+)-ATPase activity. The results emphasize the possible role of Gs-like proteins in regulation of enzymes other than adenylate cyclase and suggest that the study of (Ca2+-Mg2+)-ATPase may provide a useful enzymatic system to examine such regulation.
mesh_terms: D037361:Adenylate Cyclase Toxin; D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000037:antagonists & inhibitors*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors*; D002462:Cell Membrane / Q000201:enzymology; D002772:Cholera Toxin / Q000494:pharmacology*; D005260:Female; D019204:GTP-Binding Proteins / Q000502:physiology; D005934:Glucagon / Q000494:pharmacology*; D008099:Liver / Q000201:enzymology*; D037342:Pertussis Toxin; D051381:Rats; D011919:Rats, Inbred Strains; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
chemical_list: D037361:Adenylate Cyclase Toxin; D010566:Virulence Factors, Bordetella; D005934:Glucagon; D002772:Cholera Toxin; D037342:Pertussis Toxin; D017301:Ca(2+) Mg(2+)-ATPase; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases; D000252:Calcium-Transporting ATPases