NEUROTRANSMITTER RELEASE REGULATED BY NITRIC-OXIDE IN PC-12 CELLS ANDBRAIN SYNAPTOSOMES

Background: Nitric oxide is a messenger molecule of the nervous system , which is produced by the enzyme nitric oxide synthase, which may reg ulate cyclic guanosine monophosphate levels and which has been implica ted in the control of neurotransmitter release. PC-12 pheochromocytoma cells differentiate to form neuronal cells in culture when they are e xposed to nerve growth factor. The levels of cyclic guanosine monophos phate in the cells and their ability to release acetylcholine in respo nse to K+-depolarization are both maximal after eight days of treatmen t with nerve growth factor. We set out to assess a possible role for n itric oxide in the processes that occur in differentiating PC-12 cells . Results: Nitric oxide synthase is first evident in differentiating P C-12 cells eight days after beginning treatment with nerve growth fact or, coinciding with the marked increase in K+-depolarization-induced r elease of acetylcholine. The release of both acetylcholine and dopamin e in response to K+-depolarization is blocked by inhibitors of nitric oxide synthase and by hemoglobin, which binds nitric oxide. Providing L-arginine, a precursor required for nitric oxide synthesis, reverses the effects of the inhibitors. In synaptosomal preparations from the c orpus striatum, inhibitors of nitric oxide synthase prevent the releas e of glutamate in response to the glutamate derivative N-methyl-D-aspa rtate but not in response to K+-depolarization. Conclusion Nitric oxid e may mediate the release of acetylcholine and dopamine in response to K+-depolarization in PC-12 cells and the release of glutamate in resp onse to N-methyl-D-aspartate in striatal synaptosomes. Nitric oxide sy nthase expression is induced after eight days of treating PC-12 cells with nerve growth factor, coinciding with a marked enhancement of the release of neurotransmitters in response to K+-depolarization.