Zinc is concentrated in certain CNS excitatory tracts, especially in hippocampal mossy fibres where it has been suggested to modulate synaptic transmission and plasticity. Using rat mossy fibre synaptosomes depolarized by 4-aminopyridine, we show here that low zinc concentrations restore the membrane potential and reduce glutamate release. Both effects arose from activation of ATP-sensitive potassium channels (K ATP ), since they were mimicked by the K ATP opener diazoxide and antagonized by the K ATP blocker tolbutamide. Using recombinant channels expressed in COS-7 cells, we confirmed that micromolar zinc did activate K ATP of the type found in hippocampus. We tested the hypothesis that this action of zinc could be beneficial during an ischaemic challenge by using organotypic hippocampal slice cultures. When zinc was applied at micromolar concentrations during a brief anoxichypoglycaemic episode, it significantly attenuated the ensuing neuronal death, whereas chelation of endogenous zinc markedly aggravated cell damage. Protective effect of zinc was mediated through K ATP , as was shown by using the opener diazoxide and the blocker tolbutamide. Thus, by activating pre-synaptic K ATP channels, zinc protects neurones from hyper-excitation, excessive transmitter release and exitotoxicity, and may thus act as an endogenous neuroprotector in conditions such as epilepsy or stroke.

No abstract

Acute respiratory distress syndrome (ARDS) is characterized by an extensive alveolar capillary leak, permitting contact between intra-alveolar factors and the endothelium. To investigate whether factors contained in the alveolar milieu induce cell death in human lung microvascular endothelial cells, we exposed these cells in vitro to bronchoalveolar lavage fluid (BALF) supernatants from control patients, patients at risk of developing ARDS, and patients with early- and late-phase ARDS. In contrast to BALF from control patients, a significant cytotoxicity was found in BALF from patients at risk of developing ARDS, with late-phase ARDS, and especially from patients with early-phase ARDS. Subsequently, we determined the levels of factors known to exert cytotoxicity in endothelial cells, i.e., tumor necrosis factor (TNF)-alpha, transforming growth factor (TGF)-beta1, and angiostatin. BALF from patients at risk of developing ARDS, with early-phase ARDS, and with late-phase ARDS, contained increased levels of TNF-alpha and angiostatin, but not of TGF-beta1, as compared with BALF from control patients. Whereas inhibition of TGF-beta1 had no effect in this setting, neutralization of TNF-alpha or angiostatin inhibited the cytotoxic activity on endothelial cells of part of the early-phase ARDS BALF. These results indicate that TNF-alpha and angiostatin may contribute to ARDS-related endothelial injury.

Herein, we show that TNF exerts a pH‐dependent increase in membrane conductance in primary lung microvascular endothelial cells and peritoneal macrophages. This effect was TNF receptor‐independent, since it also occurred in cells isolated from mice deficient in both types of TNF receptors. A TNF mutant in which the three amino acids critical for the lectin‐like activity were replaced by an alanine did not show any significant effect on membrane conductance. Moreover, a synthetic 17‐amino acid peptide of TNF, which was previously shown to exert lectin‐like activity, also increased the ion permeability in these cells. The amiloride sensitivity of the observed activity suggests a binding of TNF to an endogenousion channel rather than channel formation by TNF itself. This may have important implications in mechanisms of TNF‐mediated vascular pathology.

Résumé— L'acétylcholine ‘libre’ et ‘liée’ a été mesurée avant et après stimulation de l'organe électrique de la Torpille in vivo ou in vitro, sur des tranches de tissu incubées dans une solution physiologique. Des potentiels de plaque miniatures peuvent être enregistrés. Des déharges d'une amplitude atteignant 30 V ont été obtenues après stimulation du tissu. La réponse électrique décroît rapidement lors de stimulations répétitives. L'acétylcholine ‘libre’ est celle qui est hydrolysée en cours d'homogénéisation par les estérases du tissu, l'acétyl‐choline ‘liée’ ne l'est pas. Dans l'homogénat, cette dernière est associée aux vésicules synaptiques. L'acétylcholine ‘libre’ est mesurée par la différence entre l'acétylcholine totale et l'acétylcholine ‘liée’. Une baisse d'acétylcholine ‘libre’ est mise en évidence lorsque la réponse électrophysiologique est épuisée par la stimulation. La chute d'acétylcholine ‘libre’ est, comme l'amplitude de la déharge, dépendante du rapport Ca2+/Mg2+. Dans d'autres expériences une diminution des deux compartiments a été notée à la fin de la période de stimulation. Cependant nous avons aussi observé successivement la chute de l'acétylcholine ‘libre’ puis celle de l'acétylcholine ‘liée’ lorsque la stimulation est poursuivie. En présence d'inhibiteurs d'estérase on peut recueillir de l'acétylcholine libérée par stimulation dans la solution physiologique. Une préincubation des tissus avec de la [14C]choline permet de marquer les compartiments d'acétylcholine. La radioactivité spéifique varie dans le compartiment ‘libre’ aprés une série de stimulations, alors qu'elle reste stable dans le compartiment ‘lié’. Ces résultats indiquent que l'acétylcholine ‘libre’ représente un compartiment immédiatement disponible, libéré quand on stimule le tissu.