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- and
-cells and its regulation by glucose
Departments of 1 Pediatrics and 2 Physiology, Steele Memorial Children's Research Center, University of Arizona Health Sciences Center, Tucson, Arizona 85724
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
- and
-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
- and
-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
- and
-cells, whereas VGLUT1 is only expressed
in
-cells. High (12.8 mM) and low (2.8 mM) concentrations of glucose
increased vesicular glutamate transport in
- and
-cells,
respectively. VGLUT2 mRNA was significantly increased in
- and
-cells by high and low glucose concentration, respectively.
This increase in VGLUT2 mRNA was suppressed by actinomycin D. We
conclude that both
- and
-cells possess functional vesicular glutamate transporters regulated by alteration in glucose
concentration, partly via the transcriptional mechanism.
diabetes; insulin; glucagon; transcriptional regulation
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