Involvement of Hg 2+-sensitive sulfhydryl groups in regulating noradrenaline release induced by S-nitrosocysteine in rat brain slices

Abstract

Nitric oxide has been shown to regulate neurotransmitter release. Previously, we reported that S-nitrosothiols such as S-nitrosocysteine (SNC) stimulate noradrenaline (NA) release in rat hippocampus in vivo and in vitro. To examine the role of sulfhydryl groups in SNC-induced NA release, the effects of metal ions such as Hg 2+ and N-ethylmaleimide (NEM, a sulfhydryl alkylating agent) on [ 3H]NA release from labeled rat brain slices (hippocampus and cerebral cortex) were studied and compared with the effects of SNC. The addition of 200 μM HgCl 2, but not Pb 2+, Zn 2+, or Cd 2+, stimulated [ 3H]NA release from both types of slices in the presence of extracellular CaCl 2. p-Chloromercuribenzoic acid ( p-CMBA) also stimulated [ 3H]NA release. NEM stimulated [ 3H]NA release from both types of slices in the presence and absence of extracellular CaCl 2. The effect of 200 μM NEM was enhanced, but the effect of 200 μM SNC was inhibited by co-addition of 200 μM p-CMBA in the absence of extracellular CaCl 2. The concentration–response curve of SNC shifted to the right after co-addition of 200 μM p-CMBA or 100 μM HgCl 2, although the effect of 200 μM NEM was additive to the effect of SNC. These findings demonstrate that SNC acts as a sulfhydryl agent on proteins that regulate NA release, and that SNC may share the same sulfhydryl groups with Hg compounds. The effect of T-588 {( R)-(-)-(benzo[ b]thiophen-5-yl)-2-[2-( N, N-diethylamino)ethoxy]ethanol hydrochloride}, a novel cognitive enhancer and a stimulator of NA release, was compared with the effects of sulfhydryl reagents.