Characterization of ionotropic glutamate receptors in human lymphocytes

1. The effect of L-glutamate (GIu) on human lymphocyte function was studied by measuring anti-CD3 monoclonal antibody (mAb) or phytohaemagglutinin (PHA)-induced intracellular Ca2+ ([Ca2+](i)) rise (Fura-2 method), and cell proliferation (MTT assay). 2 Glu (0.001-100 muM) did not modify basal lymphocyte [Ca2+]i, but significantly potentiated the effects of anti-CD3 mAb or PHA. Maximal [Ca2+](i) rises over resting cells were: 165 +/-8 and 247 +/- 10 nM at 3.0 x 10(-2) mg ml(-1) anti-CD3 mAb; 201 +/-4 and 266 +/-9 nM at 5.0 x 10(-2) mg ml(-1) PHA, in the absence or presence of 1 muM GIu, respectively. 3 The Glu effect showed a bell-shape concentration-dependent relationship, with a maximum (+90 +/-3% for anti-CD3 mAb and +57 +/-2% for PHA over Gill-untreated cells) at 1 muM. 4 Non-NMDA receptor agonists (1 muM) showed a greater efficacy (+76 +/-2% for (S)-AMPA; +7 +/-4% for KA), if compared to NMDA (+46 +/-2%), or Glu itself. 5 Ionotropic Glu receptor antagonists completely inhibited the effects of the corresponding specific receptor agonists (1 muM). The IC50 values calculated were: 0.9 muM for D-APS: 0.6 muM for (+)-MK801; 0.3 muM for NBQX. Both NBQX and KYNA were able to abolish GI; effect. The IC(50)s calculated were: 3.4 muM for NBQX; 0.4 muM for KYNA. 6 GIu (0.1-1 mM) did not change the resting cell proliferation, whereas GIu (I mM) significant inhibited (-27 +/-4%) PHA (1.0 x 10(-2) mg ml(-1))-induced lymphocyte proliferation at 72 h. 7 In conclusion, human lymphocytes express ionotropic GIu receptors functionally operating as modulators of cell activation.