Inhibition of noradrenaline release from PC12 cells by the long-term treatment with cholera toxin

Small-cell lung cancer (human): potentiation of endocytic membrane activity by voltage-gated Na(+) channel expression in vitro

The possible functional role of voltage-gated Na(+) channel (VGSC) expression in controlling endocytic membrane activity in human small-cell lung cancer (SCLC) cell lines (H69, H209, H510) was studied using uptake of horseradish peroxidase (HRP). The normal human airway epithelial (16HBE14o) cell line was used in a comparative approach. Uptake of HRP was vesicular, strongly temperature-sensitive and suppressed by cytoskeletal poisons (cytochalasin D and colchicine), consistent with endocytosis. Compared with the normal cells, HRP uptake into SCLC cells was kinetically more efficient, resulting in more than four-fold higher uptake under optimized conditions. Importantly, HRP uptake into SCLC cells was inhibited significantly by the specific VGSC blocker tetrodotoxin, as well as lidocaine and phenytoin. These effects were dose-dependent. None of these drugs had any effect on the uptake into the 16HBE14o cells. Uptake of HRP into SCLC cells was reduced by approximately 66% in Na(+)-free medium and was partially ( approximately 30%) dependent on extracellular Ca(2+). The possibility that the endocytic activity in the H510 SCLC cells involved an endogenous cholinergic system was investigated by testing the effects of carbachol (a cholinergic receptor agonist) and eserine (an inhibitor of acetylcholinesterase). Both drugs inhibited HRP uptake, thereby suggesting that basal cholinergic activity occurred. It is concluded that VGSC upregulation could enhance metastatic cell behavior in SCLC by enhancing endocytic membrane activity.

Effects of S-nitroso-cysteine on proteins that regulate exocytosis in PC12 cells: inhibitory effects on translocation of synaptophysin and ADP-ribosylation of GTP-binding proteins

S-Nitroso-cysteine (SNC) inhibits Ca2+-induced noradrenaline (NA) release from PC12 cells. Since SNC stimulated Ca2+ mobilization from intracellular Ca2+ pools and SNC-induced inhibition of NA release was not washed-out, SNC may modify exocytosis-related proteins that overcome Ca2+ mobilization. In the present study, we investigated the effects of SNC on exocytosis-related proteins in PC12 cells. Ionomycin stimulated NA release and increased the immunoreactivity of synaptophysin in the cytosol fraction. A 25-kDa synaptosome-associated protein (SNAP-25), which localizes to plasma membranes and vesicles, increased in the cytosol fraction after stimulation. The increases in these proteins by ionomycin were inhibited in PC12 cells treated with 0.6 mM SNC. Synaptobrevin and synapsin-1 in the cytosol fraction, and syntaxin and 43 kDa growth-associated protein in the membrane fraction were not affected by ionomycin or SNC. Incubation of each protein with SNC did not affect antibody immunoreactivity. [32P]ADP-ribosylation of GTP-binding proteins (Gi/Go) by pertussis toxin, but not Gs by cholera toxin, was inhibited in SNC-treated PC12 cells and by co-addition of SNC to the assay mixture. These findings suggest that 1) SNC inhibits translocation of vesicles containing synaptophysin and SNAP-25, and 2) SNC reacts with cysteine residues in Gi/Go, causing inhibition of ADP-ribosylation by pertussis toxin.

Involvement of Hg2+-sensitive sulfhydryl groups in regulating noradrenaline release induced by S-nitrosocysteine in rat brain slices

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 Hg2+ 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 microM HgCl2, but not Pb2+, Zn2+, or Cd2+, stimulated [3H]NA release from both types of slices in the presence of extracellular CaCl2. 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 CaCl2. The effect of 200 microM NEM was enhanced, but the effect of 200 microM SNC was inhibited by co-addition of 200 microM p-CMBA in the absence of extracellular CaCl2. The concentration-response curve of SNC shifted to the right after co-addition of 200 microM p-CMBA or 100 microM HgCl2, although the effect of 200 microM 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]eth anol hydrochloride¿, a novel cognitive enhancer and a stimulator of NA release, was compared with the effects of sulfhydryl reagents.