title: Glucose inhibits glucagon secretion by a direct effect on mouse pancreatic alpha cells.
abstract: OBJECTIVE
  The mechanisms by which glucose regulates glucagon release are poorly understood. The present study aimed to clarify the direct effects of glucose on the glucagon-releasing alpha cells and those effects mediated by paracrine islet factors.
  
  
  METHODS
  Glucagon, insulin and somatostatin release were measured from incubated mouse pancreatic islets and the cytoplasmic Ca(2+) concentration ([Ca(2+)](i)) recorded in isolated mouse alpha cells.
  
  
  RESULTS
  Glucose inhibited glucagon release with maximal effect at 7 mmol/l. Since this concentration corresponded to threshold stimulation of insulin secretion, it is unlikely that inhibition of glucagon secretion is mediated by beta cell factors. Although somatostatin secretion data seemed consistent with a role of this hormone in glucose-inhibited glucagon release, a somatostatin receptor type 2 antagonist stimulated glucagon release without diminishing the inhibitory effect of glucose. In islets exposed to tolbutamide plus 8 mmol/l K(+), glucose inhibited glucagon secretion without stimulating the release of insulin and somatostatin, indicating a direct inhibitory effect on the alpha cells that was independent of ATP-sensitive K(+) channels. Glucose lowered [Ca(2+)](i) of individual alpha cells independently of somatostatin and beta cell factors (insulin, Zn(2+) and gamma-aminobutyric acid). Glucose suppression of glucagon release was prevented by inhibitors of the sarco(endo)plasmic reticulum Ca(2+)-ATPase, which abolished the [Ca(2+)](i)-lowering effect of glucose on isolated alpha cells.
  
  
  CONCLUSIONS
  Beta cell factors or somatostatin do not seem to mediate glucose inhibition of glucagon secretion. We instead propose that glucose has a direct inhibitory effect on mouse alpha cells by suppressing a depolarising Ca(2+) store-operated current.
authors.affiliation: Department of Medical Cell Biology, Uppsala University, BMC Box 571, SE-751 23, Uppsala, Sweden.
authors.forename: E
authors.initials: E
authors.lastname: Vieira
authors.forename: A
authors.initials: A
authors.lastname: Salehi
authors.forename: E
authors.initials: E
authors.lastname: Gylfe
mesh_terms: D000818:Animals; D002118:Calcium / Q000502:physiology; D020013:Calcium Signaling; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000201:enzymology; D005934:Glucagon / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D050416:Glucagon-Secreting Cells / Q000187:drug effects / Q000378:metabolism*; D005947:Glucose / Q000494:pharmacology*; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D007700:Kinetics; D051379:Mice; D008810:Mice, Inbred C57BL; D011188:Potassium / Q000494:pharmacology; D013004:Somatostatin / Q000378:metabolism; D014044:Tolbutamide / Q000494:pharmacology
chemical_list: D007328:Insulin; D013004:Somatostatin; D005934:Glucagon; D014044:Tolbutamide; D000252:Calcium-Transporting ATPases; D005947:Glucose; D011188:Potassium; D002118:Calcium