Endothelin inhibits the calcium pump and stimulates phosphoinositide phospholipase C in liver plasma membranes via two different G proteins, Gs and Gq.
We have shown previously that in liver, endothelin (ET) binding to plasma membranes causes a rise in cytosolic calcium and activation of glycogenolysis. Here we show that the calcium extrusion pump in liver plasma membranes is inhibited by ET peptides, with ET-1 > or = ET-3 = sarafotoxin S6C-inhibition of the system being potentiated by GTP gamma S. Also, ET-1 stimulates PIP2 hydrolysis in liver plasma membranes in a guanine nucleotide-dependent manner, with ET-1 > or = ET-3 = sarafotoxin S6C. In order to determine the nature of G protein(s) coupling of the ETB receptor to both effectors, antibodies against the C-terminus of different G-protein alpha-subunits were used. Antibodies reactive with Gs alpha blocked ET-1 inhibition of the calcium pump, but they had no effect on ET-1 stimulation of PIP2 hydrolysis. Antibodies reactive with Gq alpha dose-dependently antagonized stimulation of PIP2 breakdown by ET-1 without affecting ET-1 inhibition of the calcium pump. Antibodies reactive with Gi1 alpha/Gi2 alpha had no effect on both systems. We conclude that the calcium signal induced by endothelins in hepatocytes may be consequent to both an activation of phospholipase C and inhibition of the calcium pump, both effectors being coupled to the ETB receptor by different G proteins, Gq and Gs, respectively.
Jouneaux
C
C
Unité INSERM 99, Hôpital Henri Mondor, Créteil, France.
Goldsmith
P
P
Hanoune
J
J
Lotersztajn
S
S
D000595:Amino Acid Sequence; D000818:Animals; D000252:Calcium-Transporting ATPases / Q000187:drug effects*; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology; D016232:Endothelins / Q000494:pharmacology*; D005260:Female; D019204:GTP-Binding Proteins / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D066298:In Vitro Techniques; D008099:Liver / Q000187:drug effects / Q000201:enzymology*; D008969:Molecular Sequence Data; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D014757:Viper Venoms / Q000494:pharmacology
D016232:Endothelins; D014757:Viper Venoms; C057354:sarafotoxins s6; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D010727:Phosphoric Diester Hydrolases; D019204:GTP-Binding Proteins; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D000252:Calcium-Transporting ATPases