title: Glutamine triggers and potentiates glucagon-like peptide-1 secretion by raising cytosolic Ca2+ and cAMP.
abstract: L-glutamine stimulates glucagon-like peptide 1 (GLP-1) secretion in human subjects and cell lines. As recent advances have enabled the study of primary GLP-1-releasing L cells, this study aimed to characterize glutamine-sensing pathways in native murine L cells. L cells were identified using transgenic mice with cell-specific expression of fluorescent markers. Cells were studied in primary colonic cultures from adult mice, or purified by flow cytometry for expression analysis. Intracellular Ca(2+) was monitored in cultures loaded with Fura2, and cAMP was studied using Förster resonance energy transfer sensors expressed in GLUTag cells. Asparagine, phenylalanine, and glutamine (10 mm) triggered GLP-1 release from primary cultures, but glutamine was the most efficacious, increasing secretion 1.9-fold with an EC(50) of 0.19 mm. Several amino acids triggered Ca(2+) changes in L cells, comparable in magnitude to that induced by glutamine. Glutamine-induced Ca(2+) responses were abolished in low Na(+) solution and attenuated in Ca(2+) free solution, suggesting a role for Na(+) dependent uptake and Ca(2+) influx. The greater effectiveness of glutamine as a secretagogue was paralleled by its ability to increase cAMP in GLUTag cells. Glutamine elevated intracellular cAMP to 36% of that produced by a maximal stimulus, whereas asparagine only increased intracellular cAMP by 24% and phenylalanine was without effect. Glutamine elevates both cytosolic Ca(2+) and cAMP in L cells, which may account for the effectiveness of glutamine as a GLP-1 secretagogue. Therapeutic agents like glutamine that target synergistic pathways in L cells might play a future role in the treatment of type 2 diabetes.
authors.affiliation: Cambridge Institute for Medical Research, Addenbrooke’s Hospital, Cambridge CB2 0XY, United Kingdom.
authors.forename: Gwen
authors.initials: G
authors.lastname: Tolhurst
authors.forename: Yue
authors.initials: Y
authors.lastname: Zheng
authors.forename: Helen E
authors.initials: HE
authors.lastname: Parker
authors.forename: Abdella M
authors.initials: AM
authors.lastname: Habib
authors.forename: Frank
authors.initials: F
authors.lastname: Reimann
authors.forename: Fiona M
authors.initials: FM
authors.lastname: Gribble
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism*; D005434:Flow Cytometry; D031541:Fluorescence Resonance Energy Transfer; D052216:Glucagon-Like Peptide 1 / Q000378:metabolism*; D005973:Glutamine / Q000494:pharmacology*; D051379:Mice; D020411:Oligonucleotide Array Sequence Analysis; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics
chemical_list: D005973:Glutamine; D052216:Glucagon-Like Peptide 1; D000242:Cyclic AMP; D002118:Calcium