Glucose triggers protein kinase A-dependent insulin secretion in mouse pancreatic islets through activation of the K+ATP channel-dependent pathway.
OBJECTIVE
To assess the significance of protein kinase A (PKA) in glucose triggering of ATP-sensitive K(+) (K(+)(ATP)) channel-dependent insulin secretion and in glucose amplification of K(+)(ATP) channel-independent insulin secretion.


METHODS
Insulin release from cultured perifused mouse pancreatic islets was determined by radioimmunoassay.


RESULTS
In islets cultured at 5.5 mmol/l glucose, and then perifused in physiological Krebs-Ringer medium, the PKA inhibitors, H89 (10 micromol/l) and PKI 6-22 amide (30 micromol/l) did not inhibit glucose (16.7 mmol/l)-induced insulin secretion, but inhibited stimulation by the adenylyl cyclase activator, forskolin (10 micromol/l). In the presence of 60 mmol/l K(+) and 250 micromol/l diazoxide, which stimulates maximum Ca(2+) influx independently of K(+)(ATP) channels, H89 (10 micromol/l) inhibited Ca(2+)-evoked insulin secretion, but failed to prevent glucose amplification of K(+)(ATP) channel-independent insulin secretion. In the presence of 1 mmol/l ouabain and 250 micromol/l diazoxide, which cause modest Ca(2+) influx, glucose amplification of K(+)(ATP) channel-independent insulin secretion was observed without concomitant Ca(2+) stimulation of PKA activity. In islets cultured at 16.7 mmol/l glucose, glucose (16.7 mmol/l)-induced insulin secretion in physiological Krebs-Ringer medium was augmented and now inhibited by H89 (10 micromol/l), implicating that culture at 16.7 mmol/l glucose may increase Ca(2+)-sensitive adenylyl cyclase activity and hence PKA activity. In accordance, Ca(2+)-evoked insulin secretion at 60 mmol/l K(+) and 250 micromol/l diazoxide was improved, whereas glucose amplification of K(+)(ATP) channel-independent insulin secretion was unaffected.


CONCLUSIONS
Glucose may activate PKA through triggering of the K(+)(ATP) channel-dependent pathway. Glucose amplification of K(+)(ATP) channel-independent insulin secretion, on the other hand, occurs by PKA-independent mechanisms.
Thams
Peter
P
Department of Medical Biochemistry and Genetics, The Panum Institute, University of Copenhagen, Denmark. thams@imbg.ku.dk
Anwar
Mohammad R
MR
Capito
Kirsten
K
D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000502:physiology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000502:physiology*; D003981:Diazoxide / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D005947:Glucose / Q000494:pharmacology*; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D047908:Intracellular Signaling Peptides and Proteins / Q000494:pharmacology; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D007546:Isoquinolines / Q000494:pharmacology; D008297:Male; D051379:Mice; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D015221:Potassium Channels / Q000502:physiology*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000502:physiology; D013449:Sulfonamides / Q000494:pharmacology
D007328:Insulin; D047908:Intracellular Signaling Peptides and Proteins; D007546:Isoquinolines; D015221:Potassium Channels; D013449:Sulfonamides; C015482:protein kinase modulator; D005576:Colforsin; D010042:Ouabain; D000255:Adenosine Triphosphate; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D000262:Adenylyl Cyclases; D005947:Glucose; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide; D003981:Diazoxide; D011188:Potassium; D002118:Calcium