NITRIC OXIDE-INDEPENDENT INHIBITION BY SODIUM-NITROPRUSSIDE OF THE NATIVE N-METHYL-D-ASPARTATE RECOGNITION DOMAIN IN A MANNER DIFFERENT FROM THAT BY POTASSIUM FERROCYANIDE

Binding of [H-3](+)-5-methyl-10, 11-dihydro-5H-dibenzo[a,d]cyclohepten -5,10-imine (MK-801) was significantly inhibited by the addition of so dium nitroprusside (SNP), a nitric oxide (NO) donor, at a concentratio n range of 0.1 mu M to 0.1 mM in rat brain synaptic membranes. On the contrary, two other NO donors: S-nitroso-N-acetylpenicillamine and S-n itroso-L-glutathione, did not inhibit binding even at 0.1 mM. Similarl y potent inhibition of [H-3]MK-801 binding was caused by the addition of potassium ferrocyanide, while potassium ferricyanide induced slight inhibition of binding at 0.1 mM. Both SNP and potassium ferrocyanide markedly inhibited binding of [H-3]glutamic (Glu) and 3]D,L-(E)-2-amin o-4-propyl-5-phosphono-3-pentenoic acids, without significantly affect ing that of [H-3]glycine and [H-3]5,7-dichlorokynurenic acid. Further addition of Glu significantly exacerbated the inhibition by both SNP a nd potassium ferrocyanide at concentrations of 1-10 mu M. Potent inhib ition was also induced for [H-3]MK-801 binding by the treatment of syn aptic membranes with either SNP or potassium ferrocyanide, followed by efficient washing which also inhibited [H-3]MK-801 binding due to rem oval of endogenous agonists. By con:rast, dithiothreitol clearly diffe rentiated between inhibitory properties of SNP and potassium ferrocyan ide on [H-3]MK-801 binding in terms of reversibility of the inhibition following pretreatment and subsequent washing. These results suggest that SNP may interfere with opening processes of the native NMDA chann el through molecular mechanisms different from those underlying the in hibition by potassium ferrocyanide at the NMDA recognition domain in a manner independent of the generation of NO radicals. (C) 1998 Elsevie r Science Ltd. All rights reserved.