Restitution of defective glucose-stimulated insulin secretion in diabetic GK rat by acetylcholine uncovers paradoxical stimulatory effect of beta-cell muscarinic receptor activation on cAMP production.
Because acetylcholine (ACh) is a recognized potentiator of glucose-stimulated insulin release in the normal beta-cell, we have studied ACh's effect on islets of the Goto-Kakizaki (GK) rat, a spontaneous model of type 2 diabetes. We first verified that ACh was able to restore the insulin secretory glucose competence of the GK beta-cell. Then, we demonstrated that in GK islets 1) ACh elicited a first-phase insulin release at low glucose, whereas it had no effect in Wistar; 2) total phospholipase C activity, ACh-induced inositol phosphate production, and intracellular free calcium concentration ([Ca2+]i) elevation were normal; 3) ACh triggered insulin release, even in the presence of thapsigargin, which induced a reduction of the ACh-induced [Ca2+]i response (suggesting that ACh produces amplification signals that augment the efficacy of elevated [Ca2+]i on GK exocytosis); 4) inhibition of protein kinase C did not affect [Ca2+]i nor the insulin release responses to ACh; and 5) inhibition of cAMP-dependent protein kinases (PKAs), adenylyl cyclases, or cAMP generation, while not affecting the [Ca2+]i response, significantly lowered the insulinotropic response to ACh (at low and high glucose). In conclusion, ACh acts mainly through activation of the cAMP/PKA pathway to potently enhance Ca2+-stimulated insulin release in the GK beta-cell and, in doing so, normalizes its defective glucose responsiveness.
Dolz
Manuel
M
Unité Mixte de Recherche (UMR) 7059, National Center for Scientific Research (CNRS) and Paris University 7/D. Diderot, Paris, France.
Bailbé
Danielle
D
Giroix
Marie-Hélène
MH
Calderari
Sophie
S
Gangnerau
Marie-Noelle
MN
Serradas
Patricia
P
Rickenbach
Katharina
K
Irminger
Jean-Claude
JC
Portha
Bernard
B
D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000096:biosynthesis* / Q000378:metabolism; D003924:Diabetes Mellitus, Type 2 / Q000188:drug therapy / Q000378:metabolism; D005947:Glucose / Q000494:pharmacology*; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000187:drug effects* / Q000378:metabolism*; D008297:Male; D051381:Rats; D011976:Receptors, Muscarinic / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D019284:Thapsigargin / Q000494:pharmacology
D007328:Insulin; D011976:Receptors, Muscarinic; D019284:Thapsigargin; D000242:Cyclic AMP; D005947:Glucose; D000109:Acetylcholine; D002118:Calcium