Increase in cellular glutamate levels stimulates exocytosis in pancreatic beta-cells.
Glutamate has been implicated as an intracellular messenger in the regulation of insulin secretion in response to glucose. Here we demonstrate by measurements of cell capacitance in rat pancreatic beta-cells that glutamate (1 mM) enhanced Ca2+-dependent exocytosis. Glutamate (1 mM) also stimulated insulin secretion from permeabilized rat beta-cells. The effect was dose-dependent (half-maximum at 5.1 mM) and maximal at 10 mM glutamate. Glutamate-induced exocytosis was stronger in rat beta-cells and clonal INS-1E cells compared to beta-cells isolated from mice and in parental INS-1 cells, which correlated with the expressed levels of glutamate dehydrogenase. Glutamate-induced exocytosis was inhibited by the protonophores FCCP and SF6847, by the vacuolar-type H+-ATPase inhibitor bafilomycin A(1) and by the glutamate transport inhibitor Evans Blue. Our data provide evidence that exocytosis in beta-cells can be modulated by physiological increases in cellular glutamate levels. The results suggest that stimulation of exocytosis is associated with accumulation of glutamate in the secretory granules, a process that is dependent on the transgranular proton gradient.
Høy
Marianne
M
Islet Discovery Research, Novo Nordisk A/S, Novo Alle, Bagsvaerd, Denmark.
Maechler
Pierre
P
Efanov
Alexander M
AM
Wollheim
Claes B
CB
Berggren
Per Olof
PO
Gromada
Jesper
J
D000818:Animals; D002478:Cells, Cultured; D002999:Clone Cells; D004305:Dose-Response Relationship, Drug; D025802:Electric Capacitance; D005089:Exocytosis; D018698:Glutamic Acid / Q000096:biosynthesis / Q000494:pharmacology*; D007328:Insulin / Q000378:metabolism*; D017136:Ion Transport; D007515:Islets of Langerhans / Q000378:metabolism*; D008297:Male; D051379:Mice; D011522:Protons; D051381:Rats; D017208:Rats, Wistar; D014407:Tumor Cells, Cultured
D007328:Insulin; D011522:Protons; D018698:Glutamic Acid