Endothelin action in rat liver. Receptors, free Ca2+ oscillations, and activation of glycogenolysis.
High affinity binding sites for endothelin (ET) were identified on rat liver plasma membranes. Binding of 125I-ET-1 with its site was specific, saturable, and time dependent (kobs = 0.019 +/- 0.001 min-1), but dissociation of receptor-bound ligand was minimal. A single class of high affinity binding sites for 125I-ET-1 was identified with an apparent Kd of 32.4 +/- 9.8 pM and a Bmax of 1084 +/- 118 fmol/mg protein. ET-3 and big-ET-1 (1-38) (human) inhibited 125I-ET-1 binding with IC50 values of 1.85 +/- 1.03 nM and 43 +/- 6 nM, respectively. Aequorin measurements of cytosolic free Ca2+ in single, isolated rat hepatocytes showed that ET-1 at subnanomolar concentrations induced a series of repetitive, sustained Ca2+ transients. ET-1 had no effect on cAMP production. Finally, ET-1 caused a rapid and sustained stimulation of glycogenolysis in rat hepatocytes. A 1.8-fold maximal increase in glycogen phosphorylase alpha was observed at 1 pM ET-1, with an EC50 of 0.03 pM. Stimulation of the enzyme was specific for ET-1 since the order of potency of related peptides was similar to that in binding experiments (ET-1 greater than ET-3 greater than big ET-1). These data constitute the first demonstration of the presence of ET-1 binding sites in liver which is associated with a rise in cytosolic free Ca2+ and a potent glycogenolytic effect. We conclude that ET-1 behaves as a typical Ca2+ mobilizing hormone in liver.
Serradeil-Le Gal
C
C
Sanofi Recherche, Biochimie Exploratoire, Toulouse, France.
Jouneaux
C
C
Sanchez-Bueno
A
A
Raufaste
D
D
Roche
B
B
Préaux
A M
AM
Maffrand
J P
JP
Cobbold
P H
PH
Hanoune
J
J
Lotersztajn
S
S
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D000242:Cyclic AMP / Q000096:biosynthesis; D016232:Endothelins / Q000378:metabolism / Q000494:pharmacology*; D004789:Enzyme Activation; D066298:In Vitro Techniques; D008099:Liver / Q000187:drug effects* / Q000378:metabolism; D008112:Liver Glycogen / Q000378:metabolism*; D008297:Male; D006005:Phosphorylases / Q000032:analysis; D051381:Rats; D011919:Rats, Inbred Strains; D011956:Receptors, Cell Surface / Q000032:analysis*; D017466:Receptors, Endothelin
D016232:Endothelins; D008112:Liver Glycogen; D011956:Receptors, Cell Surface; D017466:Receptors, Endothelin; D000242:Cyclic AMP; D006005:Phosphorylases; D002118:Calcium