title: Characterization of vesicular glutamate transporter in pancreatic alpha - and beta -cells and its regulation by glucose.
abstract: Glutamate has been suggested to play an important role in the release of insulin and glucagon from pancreatic cells via exocytosis. Vesicular glutamate transporter is a rate-limiting step for glutamate release and is involved in the glutamate-evoked exocytosis. Two vesicular glutamate transporters (VGLUT1 and -2) have recently been cloned from the brain. In this report, we first functionally characterized vesicular glutamate transporter in cultured pancreatic alpha- and beta-cells, and then detected mRNA expression of VGLUT1 and -2 in these cells. We also investigated the effect of high or low level of glucose on vesicular glutamate transport in cultured pancreas cells. Our results suggest that both alpha- and beta-cells contain functional vesicular glutamate transporter. The transport characteristics are similar to the cloned neuronal VGLUT1 and -2 in regard to ATP dependence, substrate specificity, kinetics, and chloride dependence. VGLUT2 mRNA is expressed in both alpha- and beta-cells, whereas VGLUT1 is only expressed in beta-cells. High (12.8 mM) and low (2.8 mM) concentrations of glucose increased vesicular glutamate transport in beta- and alpha-cells, respectively. VGLUT2 mRNA was significantly increased in beta- and alpha-cells by high and low glucose concentration, respectively. This increase in VGLUT2 mRNA was suppressed by actinomycin D. We conclude that both alpha- and beta-cells possess functional vesicular glutamate transporters regulated by alteration in glucose concentration, partly via the transcriptional mechanism.
authors.affiliation: Departments of Pediatrics and Physiology, Steele Memorial Children's Research Center, University of Arizona Health Sciences Center, Tucson, Arizona 85724, USA. fghishan@peds.arizona.edu
authors.forename: Liqun
authors.initials: L
authors.lastname: Bai
authors.forename: Xiaohong
authors.initials: X
authors.lastname: Zhang
authors.forename: Fayez K
authors.initials: FK
authors.lastname: Ghishan
mesh_terms: D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002478:Cells, Cultured; D002712:Chlorides / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects; D005947:Glucose / Q000378:metabolism / Q000494:pharmacology*; D006801:Humans; D007515:Islets of Langerhans / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D026901:Membrane Transport Proteins; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013379:Substrate Specificity; D013997:Time Factors; D050598:Vesicular Glutamate Transport Protein 1; D050599:Vesicular Glutamate Transport Protein 2; D033921:Vesicular Transport Proteins
chemical_list: D002352:Carrier Proteins; D002712:Chlorides; D026901:Membrane Transport Proteins; D012333:RNA, Messenger; C493476:SLC17A6 protein, human; C493464:SLC17A7 protein, human; D050598:Vesicular Glutamate Transport Protein 1; D050599:Vesicular Glutamate Transport Protein 2; D033921:Vesicular Transport Proteins; D005947:Glucose