Block of Ca(2+)-channels by alpha-endosulphine inhibits insulin release.
1. alpha-Endosulphine, isolated as an endogenous equivalent for sulphonylureas, is a 121-amino acids protein of 19 kDa apparent molecular mass, member of a cyclic AMP-regulated phosphoprotein family. We have previously shown that alpha-endosulphine inhibits sulphonylurea binding and K(ATP) channel activity, thereby stimulating basal insulin secretion. 2. We now describe that in the perfused rat pancreas, no stimulation was detected and that alpha-endosulphine inhibited glucose stimulated insulin release. This inhibition was dose-dependent and affected both phases of insulin secretion. 3. This inhibitory effect of alpha-endosulphine also occurred on MIN6 beta-cells when insulin release was stimulated either by glucose, sulphonylureas or a high K(+) depolarization. Inhibition was concentration-dependent with a half-maximal inhibition at 0.5 microM and was mirrored by inhibition of calcium influx. 4. Electrophysiological experiments demonstrated, in comparison to the effects of the sulphonylurea tolbutamide, that these inhibitory effects were linked to a direct inhibition of L-type Ca(2+)-channels and were independent from a regulation of K(ATP) channels. 5. Although alpha-endosulphine is able to stimulate insulin release under specific conditions acting via modulation of K(ATP) channel activity, the present study suggests that, under physiological conditions, the peptide mainly acts to block voltage-gated Ca(2+)-channels. This block leads to the inhibition of calcium influx and triggers inhibition of insulin release. 6. We conclude that alpha-endosulphine is not exclusively an endogenous equivalent for sulphonylureas and not solely a K(ATP) channel regulator.
Virsolvy
Anne
A
Institut National de la Santé et de la Recherche Médicale U376, CHU Arnaud de Villeneuve, 371 Avenue du Doyen Gaston Giraud, 34295 Montpellier Cédex 05, France. virsolvy@montp.inserm.fr
Smith
Paul
P
Bertrand
Gyslaine
G
Gros
Laurent
L
Héron
Lisa
L
Salazar
Guillermo
G
Puech
Raymond
R
Bataille
Dominique
D
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology; D029721:Drosophila Proteins; D004594:Electrophysiology; D007328:Insulin / Q000378:metabolism*; D036341:Intercellular Signaling Peptides and Proteins; D007515:Islets of Langerhans / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D023421:Models, Animal; D010179:Pancreas / Q000187:drug effects* / Q000378:metabolism; D010455:Peptides / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D029721:Drosophila Proteins; D007328:Insulin; D036341:Intercellular Signaling Peptides and Proteins; D010455:Peptides; C483180:endos protein, Drosophila; C075663:endosulfine; D002118:Calcium