title: Anomalous increase in nitric oxide synthase activity by certain nitric oxide-generating compounds in intact neuronal cells.
abstract: It has been shown that nitric oxide (NO) regulates NO synthase (NOS) activity through negative feedback in cytosolic enzyme preparations in various cell types. We compared the effects of the NO-generating compounds S-nitroso-N-acetylpenicillamine (SNAP), 3-morpholinosydnonimine (SIN-1), and sodium nitroprusside (SNP) on NOS activity in intact neuroblastoma N1E-115 cells and in the cytosol obtained from the same cells. Enzyme activity was measured by the conversion of L-[3H]arginine into L-[3H]citrulline. At concentrations that elicit almost complete inhibition of NOS activity in cytosolic enzyme preparations of these cells, SIN-1 and SNP did not cause significant attenuation of enzyme activity measured at 45 min in intact cells. It is surprising that SIN-1 and SNP markedly stimulated L-[3H]citrulline formation in a time- and concentration-dependent manner when cells were incubated with the compounds for > 1.5 h. Neither inhibitory nor stimulatory effects of SNAP on NOS were observed in intact N1E-115 cells. This is in contrast to the inhibitory effects of SNAP in cytosolic preparations of the enzyme. The increased NOS activity by SIN-1 or SNP in intact cells was dependent on the presence of extracellular Ca2+, suggesting that it might be due to increased Ca2+ influx. On the other hand, measurements of the activity of lactate dehydrogenase showed that there was no generalized increase in cell permeability in response to SIN-1 or SNP. There was no agreement in the rank order of potencies of these compounds in activating guanylate cyclase and in affecting NOS activity, both in broken-cell preparations and in intact cells.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Division of Neuroscience Research in Psychiatry, University of Minnesota School of Medicine, Minneapolis 55455, USA.
authors.forename: J
authors.initials: J
authors.lastname: Hu
authors.forename: E E
authors.initials: EE
authors.lastname: el-Fakahany
mesh_terms: D000594:Amino Acid Oxidoreductases / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002463:Cell Membrane Permeability; D006152:Cyclic GMP / Q000096:biosynthesis; D003600:Cytosol / Q000201:enzymology; D005110:Extracellular Space / Q000378:metabolism; D051379:Mice; D009474:Neurons / Q000187:drug effects* / Q000201:enzymology*; D009569:Nitric Oxide / Q000819:agonists*; D019001:Nitric Oxide Synthase; D014407:Tumor Cells, Cultured
chemical_list: D009569:Nitric Oxide; D019001:Nitric Oxide Synthase; D000594:Amino Acid Oxidoreductases; D006152:Cyclic GMP; D002118:Calcium