The neurotransmitters glycine and GABA stimulate glucagon-like peptide-1 release from the GLUTag cell line.
The incretin hormone, glucagon-like peptide-1 (GLP-1) is released from intestinal L-cells following food ingestion. Its secretion is triggered by a range of nutrients, including fats, carbohydrates and proteins. We reported previously that Na(+)-dependent glutamine uptake triggered electrical activity and GLP-1 release from the L-cell model line GLUTag. However, whereas alanine also triggered membrane depolarization and GLP-1 secretion, the response was Na+ independent. A range of alanine analogues, including d-alanine, beta-alanine, glycine and l-serine, but not d-serine, triggered similar depolarizing currents and elevation of intracellular [Ca2+], a sensitivity profile suggesting the involvement of glycine receptors. In support of this idea, glycine-induced currents and GLP-1 release were blocked by strychnine, and currents showed a 58.5 mV shift in reversal potential per 10-fold change in [Cl-], consistent with the activation of a Cl(-)-selective current. GABA, an agonist of related Cl- channels, also triggered Cl- currents and secretion, which were sensitive to picrotoxin. GABA-triggered [Ca2+]i increments were abolished by bicuculline and partially impaired by (1,2,5,6-tetrahydropyridine-4-yl)methylphosphinic acid (TPMPA), suggesting the involvement of both GABA(A) and GABA(C) receptors. Expression of GABA(A), GABA(C) and glycine receptor subunits was confirmed by RT-PCR. Glycine-triggered GLP-1 secretion was impaired by bumetanide but not bendrofluazide, suggesting that a high intracellular [Cl-] maintained by Na(+)-K(+)-2Cl- cotransporters is necessary for the depolarizing response to glycine receptor ligands. Our results suggest that GABA and glycine stimulate electrical activity and GLP-1 release from GLUTag cells by ligand-gated ion channel activation, a mechanism that might be important in responses to endogenous ligands from the enteric nervous system or dietary sources.
Gameiro
A
A
Wellcome Trust/MRC Building, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2XY, UK.
Reimann
F
F
Habib
A M
AM
O'Malley
D
D
Williams
L
L
Simpson
A K
AK
Gribble
F M
FM
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002118:Calcium / Q000378:metabolism; D045744:Cell Line, Tumor; D002712:Chlorides / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D018756:GABA Antagonists / Q000494:pharmacology; D052216:Glucagon-Like Peptide 1 / Q000378:metabolism*; D005998:Glycine / Q000494:pharmacology*; D015640:Ion Channel Gating / Q000187:drug effects; D051379:Mice; D018377:Neurotransmitter Agents / Q000494:pharmacology*; D012333:RNA, Messenger / Q000378:metabolism; D018079:Receptors, GABA / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D011963:Receptors, GABA-A / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D018009:Receptors, Glycine / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D049994:Sodium Potassium Chloride Symporter Inhibitors / Q000494:pharmacology; D028021:Sodium-Potassium-Chloride Symporters / Q000187:drug effects / Q000378:metabolism; D013331:Strychnine / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
D002712:Chlorides; D018756:GABA Antagonists; C087200:GABA-C receptor; D018377:Neurotransmitter Agents; D012333:RNA, Messenger; D018079:Receptors, GABA; D011963:Receptors, GABA-A; D018009:Receptors, Glycine; D049994:Sodium Potassium Chloride Symporter Inhibitors; D028021:Sodium-Potassium-Chloride Symporters; D005680:gamma-Aminobutyric Acid; D052216:Glucagon-Like Peptide 1; D013331:Strychnine; D002118:Calcium; D005998:Glycine