Changes in the dimeric state of neuronal nitric oxide synthase affect the kinetics of secretagogue-induced insulin response.
We previously showed that pancreatic beta-cells express a neuronal isoform of nitric oxide synthase (nNOS) that controls insulin secretion by exerting two enzymatic activities: nitric oxide (NO) production and cytochrome c reductase activity. We now bring evidence that two inhibitors of nNOS, N-omega-nitro-l-arginine methyl ester (l-NAME) and 7-nitroindazole (7-NI), increase glucose-induced insulin secretion but affect beta-cell function differently. In the presence of l-NAME, insulin response is monophasic, whereas 7-NI preserves the normal biphasic secretory pattern. In addition, the alterations of beta-cell functional response induced by the inhibitors also differ by their sensitivity to a substitutive treatment with sodium nitroprusside, a chemical NO donor. These differences are probably related to the nature of the two inhibitors. Indeed, using low-temperature SDS-PAGE and real-time analysis of nNOS dimerization by surface plasmon resonance, we could show that 7-NI, which competes with arginine and tetrahydrobiopterin (BH(4)), an essential cofactor for nNOS dimer formation, inhibits dimerization of the enzyme, whereas the substrate-based inhibitor l-NAME stabilizes the homodimeric state of nNOS. The latter effect could be reproduced by the two endogenous inhibitors of NOS, N-omega-methyl-l-arginine and asymmetric dimethylarginine, and resulted interestingly in a reduced ability of the protein inhibitor of nNOS (PIN) to dissociate nNOS dimers. We conclude that intracellular factors able to induce abnormalities in the nNOS monomer/dimer equilibrium could lead to pancreatic beta-cell dysfunction.
Lajoix
Anne-Dominique
AD
CNRS UMR 5160, Institut de Biologie, 4 Boulevard Henri IV, 34960 Montpellier Cedex 2, France.
Pugnière
Martine
M
Roquet
Françoise
F
Mani
Jean-Claude
JC
Dietz
Samuel
S
Linck
Nathalie
N
Faurie
Fleur
F
Ribes
Gérard
G
Petit
Pierre
P
Gross
René
R
D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D002352:Carrier Proteins / Q000494:pharmacology; D002460:Cell Line; D019281:Dimerization; D029721:Drosophila Proteins; D004398:Dyneins; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005947:Glucose / Q000494:pharmacology*; D007191:Indazoles / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007700:Kinetics; D008297:Male; D008825:Miconazole / Q000494:pharmacology; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D020030:Nitric Oxide Donors / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000737:chemistry* / Q000187:drug effects / Q000378:metabolism*; D052248:Nitric Oxide Synthase Type I; D019335:Nitroarginine / Q000494:pharmacology; D009599:Nitroprusside / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D020349:Surface Plasmon Resonance
D002352:Carrier Proteins; D029721:Drosophila Proteins; D004791:Enzyme Inhibitors; D007191:Indazoles; D007328:Insulin; D020030:Nitric Oxide Donors; D009599:Nitroprusside; D019335:Nitroarginine; C018524:N,N-dimethylarginine; D008825:Miconazole; D001120:Arginine; D019001:Nitric Oxide Synthase; D052248:Nitric Oxide Synthase Type I; C496322:Nos1 protein, rat; D004398:Dyneins; D005947:Glucose; C080122:7-nitroindazole; D019331:NG-Nitroarginine Methyl Ester