Gs mediates hormonal inhibition of the calcium pump in liver plasma membranes.
We have reported that the calcium pump in liver plasma membranes is coupled to Gs or a Gs-like protein. However, we show here that isoproterenol, which activated adenylyl cyclase via Gs, had no effect on the calcium pump, while human calcitonin, human parathyroid hormone, and mini-glucagon, which inhibited this system, did not affect adenylyl cyclase activity. In order to determine the nature of the G protein coupled to the calcium pump, we used the RM antibody, raised against the carboxyl-terminal decapeptide of Gs alpha, which antagonized adenylyl cyclase activation by isoproterenol or glucagon. The RM antibody specifically blocked calcium pump inhibition by mini-glucagon, calcitonin, or parathyroid hormone, while it did not affect guanosine 5'-O-(thiotriphosphate) inhibition. Its effect was mimicked by the corresponding decapeptide RMHLRQYELL. The AS/7 antibody, reactive with Gt alpha, Gi 1 alpha, and Gi2 alpha, was ineffective. Complementation of liver plasma membranes with in vitro translated Gs alpha-2, the large form of Gs alpha, led to a 40% decrease in calcium pump activity, with a parallel 2-fold increase in adenylyl cyclase activity. In vitro translated Gi1 alpha did not affect the calcium pump activity, while it evoked a 40% inhibition of adenylyl cyclase activity. We conclude that a same Gs alpha may be coupled either to the calcium pump or to adenylyl cyclase. However, Gs is functionally specialized, since it does not ensure cross-talk between the two receptor-effector systems. These results point out the possible compartmentalization of Gs.
Jouneaux
C
C
Institut National de la Santé et de la Recherche Médicale Unité 99, Hôpital Henri Mondor, Créteil, France.
Audigier
Y
Y
Goldsmith
P
P
Pecker
F
F
Lotersztajn
S
S
D000262:Adenylyl Cyclases / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D002116:Calcitonin / Q000494:pharmacology; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors*; D002462:Cell Membrane / Q000201:enzymology; D005260:Female; D019204:GTP-Binding Proteins / Q000502:physiology*; D005934:Glucagon / Q000494:pharmacology; D007158:Immunologic Techniques; D066298:In Vitro Techniques; D008099:Liver / Q000201:enzymology* / Q000648:ultrastructure; D008969:Molecular Sequence Data; D010281:Parathyroid Hormone / Q000494:pharmacology; D010455:Peptides / Q000737:chemistry / Q000276:immunology; D051381:Rats; D017208:Rats, Wistar
D010281:Parathyroid Hormone; D010455:Peptides; D002116:Calcitonin; D005934:Glucagon; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases; D000252:Calcium-Transporting ATPases