NADH-Dehydrogenases in Synaptic Plasma Membranes
Transplasma-membrane redox systems have received increasing attention in the last years as they have been found in all cells examined and appear to be a general characteristic of cells. NADH-dehydrogenase activities, using several electron acceptors, are observed in highly purified synaptic membrane preparations. These activities cannot be accounted for by microsomal or mitochondrial contamination. The NADH-dehydrogenases of synaptic membranes show a selective response to several agents: they are insensitive to rotenone, antimycin, chelating agents such as EDTA, o-phenanthroline, alpha-picolinate or nitrilotri-acetate and Nethylmaleimide; inhibition is observed with atebrin, azide, p-chloro-mercuribenzoate, and the activity vanishes upon limited proteolysis; the neuroexcitatory aminoacids Glu and Asp and their agonists markedly stimulate whereas dopamine and adrenaline strongly inhibit the NADH-acceptor oxido-reductase activities. The electron transport system is further markedly activated by antidepressants, but is unaffected by alpha- and beta-agonists or antagonists, neither by peptide hormones, opiates, adenosine, GABA and benzodiazepines, nor by nicotinic and muscarinic acids or acetylcholine.