Involvement of pertussis toxin-sensitive G-proteins in the hormonal inhibition of dihydropyridine-sensitive Ca2+ currents in an insulin-secreting cell line (RINm5F)

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Item Type:	Article
Title:	Involvement of pertussis toxin-sensitive G-proteins in the hormonal inhibition of dihydropyridine-sensitive Ca2+ currents in an insulin-secreting cell line (RINm5F)
Creators Name:	Schmidt, A., Hescheler, J., Offermanns, S., Spicher, K., Hinsch, K.D., Klinz, F.J., Codina, J., Birnbaumer, L., Gausepohl, H., Frank, R., Schultz, G. and Rosenthal, W.
Abstract:	Adrenaline inhibits insulin secretion via pertussis toxin-sensitive mechanisms. Since voltage-dependent Ca2+ currents play a key role in insulin secretion, we examined whether adrenaline modulates voltage-dependent Ca2+ currents of the rat insulinoma cell line, RINm5F. In the whole-cell configuration of the patch-clamp technique, dihydropyridine- but not omega-conotoxin-sensitive Ca2+ currents were identified. Adrenaline via alpha 2-adrenoceptors inhibited the Ca2+ currents by about 50%. Somatostatin which also inhibits insulin secretion was less efficient (inhibition by 20%). The hormonal inhibition of Ca2+ currents was not affected by intracellularly applied cAMP but blocked by the intracellularly applied GDP analog guanosine 5'-O-(2-thiodiphosphate) and by pretreatment of cells with pertussis toxin. In contrast to adrenaline and somatostatin, galanin, another inhibitor of insulin secretion, reduced Ca2+ currents by about 40% in a pertussis toxin-insensitive manner. Immunoblot experiments performed with antibodies generated against synthetic peptides revealed that membranes of RINm5F cells possess four pertussis toxin-sensitive G-proteins including Gi1, Gi2, Go2, and another Go subtype, most likely representing Go1. In membranes of control but not of pertussis toxin-treated cells, adrenaline via alpha 2-adrenoceptors stimulated incorporation of the photo-reactive GTP analog [alpha-32P]GTP azidoanilide into pertussis toxin substrates comigrating with the alpha-subunits of Gi2, Go2, and the not further identified Go subtype. The present findings indicate that activated alpha 2-adrenoceptors of RINm5F cells interact with multiple G-proteins, i.e. two forms of Go and with Gi2. These G-proteins are likely to be involved in the adrenaline-induced inhibition of dihydropyridine-sensitive Ca2+ currents and in other signal transduction pathways contributing to the adrenaline-induced inhibition of insulin secretion.
Keywords:	Calcium, Clonidine, Dihydropyridines, Polyacrylamide Gel Electrophoresis, Epinephrine, GTP-Binding Proteins, Hormones, Insulin, Insulinoma, Membrane Potentials, Pertussis Toxin, Somatostatin, Cultured Tumor Cells, Bordetella Virulence Factors, Animals, Rats
Source:	Journal of Biological Chemistry
ISSN:	0021-9258
Publisher:	American Society for Biochemistry and Molecular Biology
Volume:	266
Number:	27
Page Range:	18025-18033
Date:	25 September 1991
Official Publication:	http://www.jbc.org/cgi/content/abstract/266/27/18025
PubMed:	View item in PubMed

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