cAMP-activated protein kinase-independent potentiation of insulin secretion by cAMP is impaired in SUR1 null islets.
Whereas the loss of ATP-sensitive K(+) channel (K(ATP) channel) activity in human pancreatic beta-cells causes severe hypoglycemia in certain forms of hyperinsulinemic hypoglycemia, similar channel loss in sulfonylurea receptor-1 (SUR1) and Kir6.2 null mice yields a milder phenotype that is characterized by normoglycemia, unless the animals are stressed. While investigating potential compensatory mechanisms, we found that incretins, specifically glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP), can increase the cAMP content of Sur1KO islets but do not potentiate glucose-stimulated insulin release. This impairment is secondary to a restriction in the ability of Sur1KO beta-cells to sense cAMP correctly. Potentiation does not appear to require cAMP-activated protein kinase (PKA) because H-89 (N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide) and KT5720, inhibitors of PKA, do not affect stimulation by GLP-1, GIP, or exendin-4 in wild-type islets, although they block phosphorylation of cAMP-response element-binding protein. The impaired incretin response in Sur1KO islets is specific; the stimulation of insulin release by other modulators, including mastoparan and activators of protein kinase C, is conserved. The results suggest that the defect responsible for the loss of cAMP-induced potentiation of insulin secretion is PKA independent. We hypothesize that a reduced release of insulin in response to incretins may contribute to the unexpected normoglycemic phenotype of Sur1KO mice versus the pronounced hypoglycemia seen in neonates with loss of K(ATP) channel activity.
Nakazaki
Mitsuhiro
M
Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX 77030, USA.
Crane
Ana
A
Hu
Min
M
Seghers
Victor
V
Ullrich
Susanne
S
Aguilar-Bryan
Lydia
L
Bryan
Joseph
J
D018528:ATP-Binding Cassette Transporters; D000818:Animals; D002227:Carbazoles; D000242:Cyclic AMP / Q000502:physiology*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology*; D004789:Enzyme Activation / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005934:Glucagon; D052216:Glucagon-Like Peptide 1; D004763:Glucagon-Like Peptides; D005947:Glucose / Q000494:pharmacology; D007211:Indoles / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000378:metabolism*; D007546:Isoquinolines / Q000494:pharmacology; D051379:Mice; D018345:Mice, Knockout / Q000235:genetics; D010446:Peptide Fragments / Q000502:physiology; D015221:Potassium Channels / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D024661:Potassium Channels, Inwardly Rectifying; D011493:Protein Kinase C / Q000378:metabolism; D011758:Pyrroles / Q000494:pharmacology; D011955:Receptors, Drug / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D012016:Reference Values; D013449:Sulfonamides; D064233:Sulfonylurea Receptors
C577507:ABCC8 protein, human; D018528:ATP-Binding Cassette Transporters; C577508:Abcc8 protein, mouse; D002227:Carbazoles; D004791:Enzyme Inhibitors; D007211:Indoles; D007328:Insulin; D007546:Isoquinolines; D010446:Peptide Fragments; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D011758:Pyrroles; D011955:Receptors, Drug; D013449:Sulfonamides; D064233:Sulfonylurea Receptors; C055453:glucagon-like peptide 1 (7-36)amide; C057416:KT 5720; D004763:Glucagon-Like Peptides; D052216:Glucagon-Like Peptide 1; D005934:Glucagon; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D005947:Glucose; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide