Interaction between Calcium Chelators and the Activity of P2X7 Receptors in Mouse Motor Synapses.

The ability of P2X7 receptors to potentiate rhythmically evoked acetylcholine (ACh) release through Ca2+ entry via P2X7 receptors and via L-type voltage-dependent Ca2+ channels (VDCCs) was compared by loading Ca2+ chelators into motor nerve terminals. Neuromuscular preparations of the diaphragms of wild-type (WT) mice and pannexin-1 knockout (Panx1-/-) mice, in which ACh release is potentiated by the disinhibition of the L-type VDCCs upon the activation of P2X7 receptors, were used. Miniature end-plate potentials (MEPPs) and evoked end-plate potentials (EPPs) were recorded when the motor terminals were loaded with slow or fast Ca2+ chelators (EGTA-AM or BAPTA-AM, respectively, 50 µM). In WT and Panx1-/- mice, EGTA-AM did not change either spontaneous or evoked ACh release, while BAPTA-AM inhibited synaptic transmission by suppressing the quantal content of EPPs throughout the course of the short rhythmic train (50 Hz, 1 s). In the motor synapses of either WT or Panx1-/- mice in the presence of BAPTA-AM, the activation of P2X7 receptors by BzATP (30 µM) returned the EPP quantal content to the control level. In the neuromuscular junctions (NMJs) of Panx1-/- mice, EGTA-AM completely prevented the BzATP-induced increase in EPP quantal content. After Panx1-/- NMJs were treated with BAPTA-AM, BzATP lost its ability to enhance the EPP quantal content to above the control level. Nitrendipine (1 µM), an inhibitor of L-type VDCCs, was unable to prevent this BzATP-induced enhancement of EPP quantal content to the control level. We propose that the activation of P2X7 receptors may provide additional Ca2+ entry into motor nerve terminals, which, independent of the modulation of L-type VDCC activity, can partially reduce the buffering capacity of Ca2+ chelators, thereby providing sufficient Ca2+ signals for ACh secretion at the control level. However, the activity of both Ca2+ chelators was sufficient to eliminate Ca2+ entry via L-type VDCCs activated by P2X7 receptors and increase the EPP quantal content in the NMJs of Panx1-/- mice to above the control level.

Inhibition by EGTA of the formation of a biofilm by clinical strains of Staphylococcus aureus.

The effect of EGTA on the adhesion and on the formation of a biofilm by two reference and eight clinical strains of Staphylococcus aureus was studied. All the clinical strains were isolated from patients from Kinshasa. Spa typing confirmed that these clinical strains were distinct. The Biofilm Ring Test (BFRT®) showed that EGTA (100 µM-10 mM) inhibited the adhesion of the four clinical methicillin-resistant (MRSA) strains and the crystal violet staining method that it inhibited the formation of a biofilm by all the strains. Divalent cations abolished the effect of EGTA on the formation of a biofilm, specially in the clinical MRSA strains. EGTA had no effect on established biofilms. Only concentrations of EGTA higher than 10 mM were toxic to eukaryotic cells. Our results establish the effectiveness and the safety of lock solutions with EGTA to prevent the formation in vitro of biofilms by S. aureus.

Stimulated release of exogenous GABA and glutamate from cerebral cortical synaptosomes and brain slices by bis(acetato)tetrakis(imidazole) copper(II) complex.

In these experiments we have tested the effect of bis(acetato)tetrakis (imidazole) copper(II) on the release and uptake of 14C-GABA and 3H-glutamate from brain slices and brain cortical synaptosomes. Cu(OAc)2(Im)4 in concentrations ranging from 1 to 100 microM has increased the release of GABA and glutamate from brain slices and synaptosomal preparations in a dose-related manner when the effect on GABA release is two-fold greater than glutamate and 10-fold greater than alanine. Pretreatment with a GABA uptake inhibitor such as 1-2 mM nipecotic acid has no effect on 14C-GABA release, whereas hydroxy aspartate, the glutamate uptake inhibitor, has elevated the stimulated release of glutamate. Copper(II) chloride, the inorganic form of copper, had no significant effect either on GABA release or on glutamate release. The stimulated release of exogenous GABA and glutamate was Ca2+-dependent, because it was inhibited by EGTA, and neuronal, because it was blocked by tetrodotoxin. The recent results can explain the anticonvulsant activity of Cu(OAc)2(Im)4 against strychnine-induced seizures by increasing the net release of GABA from cortical neurons.

Cadmium-induced cell transformation and tumorigenesis are associated with transcriptional activation of c-fos, c-jun, and c-myc proto-oncogenes: role of cellular calcium and reactive oxygen species.

The molecular mechanisms of carcinogenesis by cadmium were studied using BALB/c-3T3 cell transformation and nude mouse tumorigenesis models. BALB/c-3T3 cells transformed with cadmium chloride were subcutaneously injected into nude mice to develop tumors and the cell lines derived from these tumors were used in the present study. The proto-oncogenes c-fos and c-jun were overexpressed in 100% (10 out of 10) of the cell lines, while a statistically significant overexpression of c-myc was observed in 40% (4 out of 10) of the cell lines. Analysis of tumor cells stained with fluorescent dyes specific for reactive oxygen species revealed that these cells possessed markedly higher levels of superoxide anion and hydrogen peroxide compared with the nontransformed cells. Similarly, the intracellular calcium level was higher in the tumor cells compared with the nontransformed cells. Overexpression of the proto-oncogenes in these cells was blocked by treating the cells with superoxide dismutase, catalase, and 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetra acetoxy methyl ester (BAPTA/AM), which are scavengers of superoxide anion, hydrogen peroxide, and calcium, respectively. This confirmed that the overexpression of the proto-oncogenes in the tumor cells required elevated intracellular levels of reactive oxygen species and calcium. In addition to the scavengers of reactive oxygen species and calcium, inhibitors specific for transcription (actinomycin D), protein kinase C (RO-31-8220), and MAP kinase (PD 98059) also blocked the cadmium-induced overexpression of the proto-oncogenes in the tumor cells. Exposure of the nontransformed BALB/c-3T3 cells to 20 microM cadmium chloride for 1 h caused elevated intracellular levels of superoxide anion, hydrogen peroxide, and calcium, with corresponding increases in the expression levels of c-fos, c-jun, and c-myc. As in the case of the tumor cells, treating the nontransformed cells with the various modulators prior to their exposure to cadmium chloride resulted in inhibition in the expression of the proto-oncogenes. Based on these data, we conclude that the cadmium-induced overexpression of cellular proto-oncogenes is mediated by the elevation of intracellular levels of superoxide anion, hydrogen peroxide, and calcium. Further, the cadmium-induced overexpression of the proto-oncogenes is dependent on transcriptional activation as well as on pathways involving protein kinase C and MAP kinase.

Ca2+-dependent and Ca2+-independent excretion modes of salicylic acid in tobacco cell suspension culture.

14C-salicylic acid (SA) was used to monitor SA metabolism and its regulation in tobacco cell suspension culture. Two SA concentrations (20 microM and 200 microM) were used for comparison. SA was quickly taken up in both treatments, and the 200 microM-treated cells absorbed approximately 15 times that of 20 microM-treated cells within 5 min. More than 85% and 50% of the absorbed SA were excreted in free form to the culture medium within 5 h from cells treated with 200 microM and 20 microM SA, respectively. SA excretion was significantly inhibited by EGTA and the inhibition could be reversed by the addition of exogenous Ca2+ to the culture medium in the 200 microM SA treatment. However, EGTA had little or no effect on SA excretion in the 20 microM SA treatment. The data suggest that tobacco suspension-cultured cells may contain both Ca2+-dependent and Ca2+-independent pathways for SA excretion. Reduced glutathione (an active oxygen species scavenger), staurosporine (a protein kinase inhibitor), and cycloheximide (an inhibitor of de novo protein synthesis) also blocked intracellular SA excretion to the culture medium in the 200 microM but not in the 20 microM SA treatment. These data support the existence of alternative SA excretion pathways in tobacco suspension-cultured cells. Tobacco cells may use both Ca2+-dependent and Ca2+-independent excretion pathways to cope with different intracellular SA status, and the pathway influenced by EGTA, reduced glutathione, staurosporine, and cycloheximide is activated by SA at 200 microM, but not at 20 microM.