Pharmacological and molecular characterization of glutamate receptors in the MIN6 pancreatic beta-cell line

The MIN6 pancreatic beta-cell line responds to glutamate, alpha-amino-3-hyd roxy-5-methyl-4-isoxazolepropionic acid (AMPA) and kainate, but not N-methy l-D-aspartate (NMDA) or 1S,3R-trans-ACPD, with increases in [Ca2+](i). This correlates with MIN6 expression of AMPA receptor subunits (GluR1-4) but on ly weak expression of NMDA NR2 receptor subunits, as determined by reverse transcriptase polymerase chain reaction (RT-PCR). Pharmacological character ization of the MIN6 AMPA receptors showed that AMPA-triggered [Ca2+](i) res ponses were blocked by GYKI 52466, 6-cyano-7-nitroquinoxaline-2,3-dione (CN QX) and pentobarbital. AMPA-triggered [Ca2+](i) responses were also blocked in Na+-free medium and by the voltage-sensitive Ca2+ channel antagonist La 3+. Unlike cortical neuronal cultures, which show a loss of membrane-associ ated protein kinase C (PKC) activity and die in response to excitatory amin o acid exposure, glutamate was not toxic to MIN6 cells and it did not decre ase PKC activity. These studies indicate that MIN6 cells possess Ca2+-imper meable AMPA receptors that secondarily allow Ca2+ influx following AMPA-ind uced depolarization and that, despite elevating [Ca2+](i), AMPA is not toxi c to these cells. The effects of glutamate and glutamate receptor antagonis ts on pancreatic cells needs to be better understood if these compounds are to be used as therapeutic agents to treat stroke.