AMPA receptor activation regulates the glutamate metabotropic receptor stimulated phosphatidylinositol turnover in human cerebral cortex slices

Abstract

The effect of excitatory amino acids (EAA) on phosphatidylinositol (PI) turnover in human cerebral cortical slices was investigated. Trans-1-aminocyclopentane-1,3-dicarboxylic acid (ACPD) increased inositol phosphate (IP) formation in the 1–1000 μM range. Quisqualic acid (QA) was maximally effective at 10–100 μM, showing an inverse correlation between concentration and effect in the 100–1000 μM range. The glutamate metabotropic receptor antagonist 2-amino-3-phosphonopropionic acid (AP3), the ionotropic non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and the NMDA channel blocker dizolcipine (MK-801) failed to prevent the PI response to ACPD (1000 μM). However, CNQX (100 μM) modified the concentration-response curve of QA reducing the effect of QA 10 μM by approx. 50% and enhancing that of QA 1000 μM by 2-fold. In addition, CNQX (100 μM) together with MK-801 (100 μM) unmasked the ability of l-glutamate (L-GLU) 3000 μM to stimulate PI turnover. The effect of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) on the EAA-induced PI turnover was also studied. AMPA (0.1–1 μM) potentiated the response to submaximal (30 μM) ACPD and (1 μM) QA concentrations. However, higher AMPA concentrations(10 μM) failed to synergize with ACPD 30 μM and, in addition, inhibited the PI turnover maximally stimulated by QA 10 μM. These results further support the presence of the glutamate metabotropic receptor in the human neocortex. In addition, they show the occurrence of a concentration-related dual interaction between AMPA and glutamate metabotropic receptor activation in the IP formation in this brain area.