Glucose-sensing in glucagon-like peptide-1-secreting cells.
Glucagon-like peptide-1 (GLP-1) is released from intestinal L-cells in response to carbohydrate and fat in the diet. Despite the interest in GLP-1 as an antidiabetic agent, very little is known about the mechanism of stimulus-secretion coupling in L-cells. We investigated the electrophysiological events underlying glucose-induced GLP-1 release in the GLP-1-secreting cell line, GLUTag. Cells were studied using perforated-patch and standard whole-cell patch clamp recordings. GLUTag cells were largely quiescent and hyperpolarized in the absence of glucose. Increasing the glucose concentration between 0 and 20 mmol/l decreased the membrane conductance, caused membrane depolarization, and triggered the generation of action potentials. Action potentials were also triggered by tolbutamide (500 micro mol/l) and were suppressed by diazoxide (340 micro mol/l) or the metabolic inhibitor azide (3 mmol/l), suggesting an involvement of K(ATP) channels. Large tolbutamide-sensitive washout currents developed in standard whole-cell recordings, confirming the presence of K(ATP) channels. RT-PCR detected the K(ATP) channel subunits Kir6.2 and SUR1 and glucokinase. GLP-1 secretion was also stimulated by glucose over the concentration range 0-25 mmol/l and by tolbutamide. Our results suggest that glucose triggers GLP-1 release through closure of K(ATP) channels and action potential generation.
Department of Clinical Biochemistry, University of Cambridge, Addenbrooke's Hospital, Hills Road, Cambridge, U.K.
Frank
F
Reimann
Fiona M
FM
Gribble
D000200:Action Potentials / Q000187:drug effects; D000255:Adenosine Triphosphate / Q000502:physiology; D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000502:physiology; D003981:Diazoxide / Q000494:pharmacology; D004553:Electric Conductivity; D005934:Glucagon / Q000378:metabolism*; D052216:Glucagon-Like Peptide 1; D005941:Glucokinase / Q000378:metabolism; D005947:Glucose / Q000378:metabolism* / Q000494:pharmacology; D016695:Glycosyltransferases; D007004:Hypoglycemic Agents / Q000494:pharmacology; D008565:Membrane Proteins; D010446:Peptide Fragments / Q000378:metabolism*; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology; D024661:Potassium Channels, Inwardly Rectifying / Q000378:metabolism; D011498:Protein Precursors / Q000378:metabolism*; D012097:Repressor Proteins / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D029701:Saccharomyces cerevisiae Proteins; D014044:Tolbutamide / Q000494:pharmacology
D007004:Hypoglycemic Agents; D008565:Membrane Proteins; D010446:Peptide Fragments; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D011498:Protein Precursors; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D052216:Glucagon-Like Peptide 1; D000255:Adenosine Triphosphate; D005934:Glucagon; D014044:Tolbutamide; D016695:Glycosyltransferases; C092031:SUR1 protein, S cerevisiae; D005941:Glucokinase; D005947:Glucose; D003981:Diazoxide