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 front al cortex and hippocampus by measuring the conversion of L-[H-3]argini ne to L-[H-3]citrulline, N-methyl-D-aspartate (NMDA), but not kainate or pha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA), stimulat ed NOS activity. This effect was concentration dependent (EC(50) appro ximate to 30 mu M) and was inhibited by tetrodotoxin, EGTA, N-omega-ni tro-L-arginine (NOARG), Mg2+, phencyclidine, and (cis)-4-phosphonometh yl-2-piperidine carboxylate (CGS 19755), but not by 6-cyano-7-nitroqui noxaline-2,3-dione (CNQX). NOS activity was increased to an even great er extent by the calcium ionophores ionomycin and A23187 and by depola rization with 50 mM K+. Interestingly, neither caffeine nor 1-aminocyc lopentane-1,3-dicarboxylic acid (1S,3R-ACPD), drugs that would be expe cted to increase intracellular Ca2+ concentration by release of Ca2+ f rom intracellular ryanodine- and inositol-1,4,5-trisphosphate-sensitiv e stores, respectively, had any significant effect on NOS activity. It is concluded that NOS can be activated by NMDA binding to a classic N MDA glutamate receptor subtype as well as by depolarization or other a gents that increase the influx of extracellular Ca2+ The paradoxical l ack of effect of caffeine, as well as the inhibitory effect of tetrodo toxin, are discussed. (C) 1994 Wiley-Liss, Inc.