Insulin induces Ca2+ influx into isolated rat hepatocyte couplets.
Isolated rat hepatocyte couplets were used to study the direct effect of insulin on intracellular Ca2+ homeostasis. Insulin induced a dose-dependent increase in hepatocellular Ca2+ that was gradual, generally monophasic, and reversible. Chelation of extracellular Ca2+ abolished the insulin-induced Ca2+ response, and this suppression was not related to an effect on insulin binding, as indicated by displacement studies. We thus tested the effect of several Ca2+ channel inhibitors on insulin-induced Ca2+ influx. Verapamil at 20 or 200 microM was without effect, whereas 500 microM nickel and 50 microM gadolinium strongly inhibited insulin-induced Ca2+ entry. Finally, we tested whether insulin-induced Ca2+ movements were implicated in the stimulation of mitogen-activated protein kinase (MAPK) activity, which we measured with the use of an immune-complex assay. Verapamil was without effect on the insulin-dependent stimulation of p44mapk activity, whereas addition of ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid, nickel, or gadolinium strongly inhibited the effect of the peptide hormone. Our results indicate that insulin triggers Ca2+ influx into hepatocytes, possibly through the opening of channels on the plasma membrane, and that this effect is important for insulin activation of MAPK.
Benzeroual
K
K
Départment de Pharmacologie, Université de Montréal, Québec, Canada.
van de Werve
G
G
Meloche
S
S
Mathé
L
L
Romanelli
A
A
Haddad
P
P
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002478:Cells, Cultured; D002614:Chelating Agents / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D005456:Fluorescent Dyes; D016257:Fura-2 / Q000031:analogs & derivatives; D005682:Gadolinium / Q000494:pharmacology; D006706:Homeostasis; D007328:Insulin / Q000494:pharmacology*; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D009532:Nickel / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013050:Spectrometry, Fluorescence; D014700:Verapamil / Q000494:pharmacology
D002614:Chelating Agents; D005456:Fluorescent Dyes; D007328:Insulin; C049925:fura-2-am; D010656:Phenylephrine; D004533:Egtazic Acid; D009532:Nickel; D005682:Gadolinium; D014700:Verapamil; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002118:Calcium; D016257:Fura-2