Micromolar Concentrations Of Zinc Research Articles

Zinc Regulates Chemical‐Transmitter Storage in Nanometer Vesicles and Exocytosis Dynamics as Measured by Amperometry

AbstractWe applied electrochemical techniques with nano‐tip electrodes to show that micromolar concentrations of zinc not only trigger changes in the dynamics of exocytosis, but also vesicle content in a model cell line. The vesicle catecholamine content in PC12 cells is significantly decreased after 100 μm zinc treatment, but, catecholamine release during exocytosis remains nearly the same. This contrasts with the number of molecules stored in the exocytosis vesicles, which decreases, and we find that the amount of catecholamine released from zinc‐treated cells reaches nearly 100 % content expelled. Further investigation shows that zinc slows down exocytotic release. Our results provide the missing link between zinc and the regulation of neurotransmitter release processes, which might be important in memory formation and storage.

Zinc Regulates Chemical-Transmitter Storage in Nanometer Vesicles and Exocytosis Dynamics as Measured by Amperometry.

We applied electrochemical techniques with nano-tip electrodes to show that micromolar concentrations of zinc not only trigger changes in the dynamics of exocytosis, but also vesicle content in a model cell line. The vesicle catecholamine content in PC12 cells is significantly decreased after 100 μm zinc treatment, but, catecholamine release during exocytosis remains nearly the same. This contrasts with the number of molecules stored in the exocytosis vesicles, which decreases, and we find that the amount of catecholamine released from zinc-treated cells reaches nearly 100 % content expelled. Further investigation shows that zinc slows down exocytotic release. Our results provide the missing link between zinc and the regulation of neurotransmitter release processes, which might be important in memory formation and storage.

Effects of zinc ex vivo on taurine uptake in goldfish retinal cells

BackgroundTaurine and zinc exert neurotrophic effects in the central nervous system. Current studies demonstrate that Na+/Cl- dependent neurotransmitter transporters, similar to that of taurine, are modulated by micromolar concentrations of zinc. This study examined the effect of zinc sulfate ex vivo on [3H]taurine transport in goldfish retina.MethodsIsolated cells were incubated in Ringer with zinc (0.1–100 µM). Taurine transport was done with 50 nM [3H]taurine or by isotopic dilution with taurine (0.001–1 mM) and 50 nM [3H]taurine.ResultsZinc reduced the capacity of taurine transport without changes in affinity, and caused a noncompetitive inhibition of high affinity taurine transport, with an EC50= 0.072 µM. The mechanism by which zinc affects taurine transport is unknown at the present.ConclusionsThere may be a binding site of zinc in the transporter that affects union or translocation of taurine, or possibly the formation of taurine-zinc complexes, rather than free zinc, could affect the operation of the transporter.

The role of the siderophore pyridine-2,6-bis (thiocarboxylic acid) (PDTC) in zinc utilization by Pseudomonas putida DSM 3601

Previous work had suggested that in addition to serving the function of a siderophore, pyridine-2,6-bis(thiocarboxylic acid) (PDTC) may also provide producing organisms with the ability to assimilate other divalent transition metals. This was tested further by examining regulation of siderophore production, expression of pdt genes, and growth in response to added zinc. In media containing 10-50 microM ZnCl2, the production of PDTC was found to be differentially repressed, as compared with the production of pyoverdine. The expression of PdtK, the outer membrane receptor involved in PDTC transport, was also reduced in response to added zinc whereas other iron-regulated outer membrane proteins were not. Expression of a chromosomal pdtI: xylE fusion was repressed to a similar extent in response to zinc or iron. Mutants that cannot produce PDTC did not show a growth enhancement with micromolar concentrations of zinc as seen in the wild type strain. The phenotype of the mutant strains was suppressed by the addition of PDTC. The outer membrane receptor and inner membrane permease components of PDTC utilization were necessary for relief of chelator (1,10-phenanthroline)-induced growth inhibition by Zn:PDTC. Iron uptake from 55Fe:PDTC was not affected by a 32-fold molar excess of Zn:PDTC. The data indicate that zinc present as Zn:PDTC can be utilized by strains possessing PDTC utilization functions but that transport is much less efficient than for Fe:PDTC.

Zinc as a Cofactor for Heparin Neutralization by Histidine-rich Glycoprotein

We have studied the ability of histidine-rich glycoprotein (HRG) to neutralize the anticoagulant activity of heparin in plasma and in a purified component clotting assay. Addition of HRG to plasma or to the purified component assay did not neutralize the anticoagulant activity of heparin unless micromolar concentrations of zinc were present. Higher zinc concentrations were required for citrated than for heparinized plasmas due to competition of citrate with HRG for zinc binding. Zinc concentrations as low as 1.25 microM revealed HRG to be a powerful competitor of antithrombin for heparin in the purified component assays. HRG binding of heparin also was shown by affinity chromatography of HRG from immobilized heparin in the presence and absence of zinc. In the absence of zinc, HRG was eluted by 0.1 M NaCl, but, in the presence of zinc, elution of HRG required 1.0 M NaCl. Investigation of other divalent cations (copper and magnesium) indicated that augmentation of heparin binding by HRG in the presence of antithrombin was restricted to zinc. The HRG.Zn complex effectively competes with antithrombin for heparin, which restricts the availability of heparin to bind antithrombin and allows thrombin-mediated fibrinogenesis to proceed unimpeded. This could be initiated by zinc released from activated platelets.

Interaction between the zinc(II) and the heparin binding site of the Alzheimer's disease βA4 amyloid precursor protein (APP)

The Alzheimer's disease βA4 amyloid precursor protein (APP) has been suggested to be involved in regulation of cell growth, neurite outgrowth and adhesiveness through binding to heparin sulfate proteoglycans. In order to unravel the molecular mechanisms underlying those functions in vitro we show that APP binds in a time dependent and saturable manner to the glycosaminoglycan side-chains of proteoglycans but not to chondroitinsulfate. We also demonstrate an interaction between the high affinity heparin binding site within the carbohydrate domain of APP and the zinc(II) binding site of APP. We show that the affinity for heparin is increased two- to four-fold in the presence of micromolar zinc(II). Thus micromolar concentrations of zinc(II) appear to be able to modulate the binding of APP to heparin side-chains of proteoglycans and as shown previously [Science 265 (1994) 1464–1467] to induce the aggregation of soluble amyloid βA4 protein.

Studies with an automated kinetic assay for plasma angiotensin-converting enzyme activity and its potentiation by zinc ion

Measurement of plasma angiotensin-converting enzyme (ACE) is of value in sarcoidosis and, when specific inhibitors are prescribed therapeutically, in hypertension and heart failure. In this study a rapid kinetic assay for estimation of plasma ACE is described and assessed. In particular the effects of zinc ion have been studied. In contrast to previous reports, a marked potentiation of ACE activity by micromolar concentrations of zinc was noted. The relationship between plasma zinc concentration and ACE activity in vivo was also investigated and related to albumin concentration. The findings may have implications for interpretation of plasma ACE activity in patients with low plasma zinc levels.

Inhibition of LPS toxicity for macrophages by metallothionein-inducing agents.

Parenteral administration of adrenal corticosteroids or particular transition metal salts are known to protect mice from the lethal effects of bacterial lipopolysaccharides (LPS). To determine if both groups of substances act through similar biologic mechanisms, their capacity to protect macrophages from the direct toxic effects of LPS was examined in vitro. When added simultaneously with LPS at culture initiation, 10 to 100 microM cortisone increased the viability of normal peritoneal macrophages as determined by trypan blue exclusion. Prednisolone and corticosterone protected LPS-treated macrophages at even lower concentrations (0.1 to 1 microM); estradiol and testosterone failed to alter cell viability at any concentration tested. Protection was dependent on de novo synthesis because inclusion of 20 nM actinomycin C1 or 1 microM cycloheximide with 10 microM corticosterone during a 4-hr pretreatment period blocked induction of the protective effect. Murine macrophages were also protected by micromolar concentrations of zinc, cadmium, mercury, and manganese, but not by calcium or lead. As was obtained with corticosteroids, heavy metal-induced protection depended on de novo RNA and protein synthesis. Because all substances that protected against LPS are known inducers of metallothionein in somatic cells, peritoneal macrophages were assayed for the presence of this unique, cytoplasmic protein. Within 2 to 8 hr, 10 microM cadmium caused three to fivefold increases in the incorporation of 35S-cysteine and in the binding of 203Hg into the TCA-soluble fraction of cell lysates that was excluded on centrifugally accelerated Sephadex G-10 columns. These results suggest macrophages may be protected from LPS-mediated cytotoxicity through synthesis of a sulfhydryl-rich, metal-binding protein. Although its mechanism of action remains unknown, it is proposed that metallothionein may function homeostatically by altering intracellular concentrations of zinc or may play a regulatory role by facilitating transfer of heavy metals among metal-requiring apoproteins.