GLUTAMATE STIMULATES GLUCAGON-SECRETION VIA AN EXCITATORY AMINO-ACID RECEPTOR OF THE AMPA SUBTYPE IN RAT PANCREAS

The effect of L-glutamate was studied on glucagon secretion from rat isolated pancreas perfused with 2.8 mM glucose. L-Glutamate (3.10(-5)-10(-4) M) induced an immediate, transient and concentration-dependent glucagon release. The three non-N-methyl-D-aspartate (NMDA) receptor agonists, kainate (3.10(-5)-3.10(-3) M), alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) (3.10(-5)-10(-4) M) and quisqualate (3.10(-6)-10(-5) M), all elicited a peak-shaped glucagon response. Compared to glutamate, AMPA and quisqualate exhibited a similar efficacy, whereas kainate caused a 4-fold higher maximal glucagon response. In contrast, NMDA (10(-3) M) was ineffective. The selective antagonist of non-NMDA receptors, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; 5.10(-5) M), totally prevented the glucagon response to 10(-4) M glutamate (IC50 congruent-to 0.8 +/- 0.3 10(-6) M) and 3.10(-4) M kainate. Furthermore, quisqualate at a maximal effective concentration (3.10(-4) M) inhibited the response to kainate (10(-3) M). This study showed that L-glutamate stimulates glucagon release in rat pancreas by activating a receptor of the AMPA subtype.