REGULATION OF NITRIC-OXIDE SYNTHASE ACTIVITY IN CORTICAL SLICES BY EXCITATORY AMINO-ACIDS AND CALCIUM

Nitric oxide synthase (NOS) activity was determined in adult rat frontal cortex and hippocampus by measuring the conversion of L-[H-3]arginine to L-[H-3]citrulline, N-methyl-D-aspartate (NMDA), but not kainate or alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA), stimulated NOS activity. This effect was concentration dependent (EC(50) approximate to 30 mu M) and was inhibited by tetrodotoxin, EGTA, N-omega-nitro-L-arginine (NOARG), Mg2+, phencyclidine, and (cis)-4-phosphonomethyl-2-piperidine carboxylate (CGS 19755), but not by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). NOS activity was increased to an even greater extent by the calcium ionophores ionomycin and A23187 and by depolarization with 50 mM K+. Interestingly, neither caffeine nor 1-aminocyclopentane-1,3-dicarboxylic acid (1S,3R-ACPD), drugs that would be expected to increase intracellular Ca2+ concentration by release of Ca2+ from intracellular ryanodine- and inositol-1,4,5-trisphosphate-sensitive stores, respectively, had any significant effect on NOS activity. It is concluded that NOS can be activated by NMDA binding to a classic NMDA glutamate receptor subtype as well as by depolarization or other agents that increase the influx of extracellular Ca2+ The paradoxical lack of effect of caffeine, as well as the inhibitory effect of tetrodotoxin, are discussed. (C) 1994 Wiley-Liss, Inc.