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J. Biol. Chem., Vol. 265, Issue 17, 9876-9880, Jun, 1990
Glucagon-(19-29) exerts a biphasic action on the liver plasma membrane Ca2+ pump which is mediated by G proteins
S Lotersztajn, C Pavoine, V Brechler, B Roche, M Dufour, D Le-Nguyen, D Bataille and F Pecker
Institut National de la Sante et de la Recherche Medicale, Unite 99, Hopital Henri Mondor, Creteil, France.
We have recently shown that nanomolar concentrations of glucagon-(19- 29),
which can derive from native glucagon by proteolytic cleavage of the
dibasic doublet Arg17-Arg18, inhibit the Ca2+ pump in liver plasma membrane
vesicles independently of adenylyl cyclase activation (Mallat, A., Pavoine,
C., Dufour, M., Lotersztajn, S., Bataille, D., and Pecker, F. (1987) Nature
325, 620-622). We report here that the regulation of the Ca2+ pump by
glucagon-(19-29) is dependent on guanine nucleotides. In the presence of 10
microM guanosine 5'-3-O-(thio) triphosphate (GTP gamma S) or 75 microM GTP,
glucagon-(19-29) caused a biphasic regulation of the Ca2+ pump.
ATP-dependent Ca2+ transport was inhibited in the presence of 10 pM to 1 nM
glucagon-(19-29), while higher concentrations of the peptide (1-100 nM)
reversed the inhibition caused by lower ones. GTP gamma S alone, at high
concentrations (100 microM), reproduced the inhibitory effect of
glucagon-(19-29) and induced a 40% inhibition of the basal activity of the
Ca2+ pump which was reversed by low concentrations of glucagon-(19-29) (10
pM to 1 nM). Treatment of rats with cholera toxin resulted in a 70%
increase in the basal activity of the Ca2+ pump, a loss of sensitivity to
GTP gamma S and to the biphasic regulation by glucagon-(19-29). Treatment
with pertussis toxin did not affect the response of the Ca2+ pump to GTP
gamma S and glucagon-(19-29). We conclude that glucagon-(19-29) can exert a
biphasic effect on the Ca2+ pump which is mediated by G protein(s)
sensitive to cholera toxin.

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Copyright © 1990 by the American Society for Biochemistry and Molecular Biology.
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