Tumor promoter 12-0-tetradecanoyl-phorbol-13-acetate (TPA) can reduce the Ca-transporting ability of Ca-ionophores in T lymphocytes: the involvement of intracellular heavy metal ions

Micromolar zinc affects endonucleolytic activity in hydrogen peroxide-mediated apoptosis

When damaged by hydrogen peroxide, peripheral blood lymphocytes undergo cell death by apoptosis in the absence of internucleosomal DNA cleavage, while, in the same cells, other apoptosis-inducing treatments bring DNA cleavage to completion. However, the formation of internucleosomal DNA fragments is readily obtained if cells are pretreated with a divalent metal chelator, TPEN, at micromolar concentrations. Since the coadministration of equimolar zinc concentrations abrogates the formation of the ladder, a zinc-inhibitable endonucleolytic activity is accounted for the effect. Most notably, subtraction of zinc ions does not increase the percentage of cells undergoing apoptosis, but rather results in a rescue from death.

Chronic overcrowding decreases cytoplasmic free calcium levels in T lymphocytes of aged CBA/CA mice

Intracellular calcium concentration is a sensitive marker of the homeostasis of living cells, and its increase is an essential step of T lymphocyte activation. Changes in the environment provoke an adaptive stress-response of the organism. In our present work we have investigated the effect of chronic overcrowding on resting and lectin-stimulated cytoplasmic free calcium concentration of splenic T lymphocytes from young and aged CBA/CA mice (50 animals total). The animals were kept under 'normal' (68 cm2/animal) or 'overcrowded' (22 cm2/animal) conditions for 3 months. Young animals showed no change in resting and stimulated calcium after overcrowding. T cells from aged mice, however, displayed significantly smaller levels of both resting and lectin-stimulated intracellular calcium concentration (p < 0.01 each), as compared to those of the non-stressed, aged animals. This inadequate adaptation in the calcium metabolism of T lymphocytes may significantly contribute to the diminished immune response of the aged in stress.

The nonapeptide leucinostatin A acts as a weak ionophore and as an immunosuppressant on T lymphocytes

Earlier studies have disclosed that leucinostatin A, a hydrophobic nonapeptide antibiotic, assumes an alpha-helical secondary structure in nonpolar environments. The present report demonstrates that the peptide acts as a weak ionophore facilitating the transport of mono-and divalent cations through the plasma membrane of T lymphocytes and through artificial membranes. Leucinostatin A does not change the thymidine uptake of both resting mouse thymocytes and peripheral blood lymphocytes but dose-dependently prevents the activation of T lymphocytes by tetradecanoyl-phorbol-acetate and by anti-T cell receptor antibody.

Hypochlorous acid-induced mobilization of zinc from metalloproteins

Hypochlorous acid (HOCl), a neutrophil oxidant, can contribute to tissue injury at sites of inflammation by its reactivity with protein sulfhydryls. The present study shows that physiological concentrations (50-200 microM) of HOCl can displace Zn2+ from metalloproteins, such as metallothionein and alcohol dehydrogenase, in which the metal is bound to sulfhydryls by means of thiolate (S-Zn) bonds. No mobilization of Zn2+ was observed from superoxide dismutase in which the metal is not bound to cysteine, suggesting that HOCl reacts selectively with thiolate bonds. Zn2+ mobilization, measured spectrophotometrically with the metallochromic indicator 4-(2-pyridylazo)resorcinol, was also observed from complexes of this metal with other thiol-containing compounds such as 2,3-dimercaptopropanol and metallothionein fragment 56-61. HOCl cleavage of the thiolate bonds was confirmed by the decrease in absorbance at 250 nm. This study shows for the first time that HOCl can mobilize protein-bound Zn2+ and suggests that neutrophil oxidant injury may be partially mediated by the mobilization of cellular Zn2+.

Non-calcium environmental sensitivity of intracellular Indo-1

Several mechanisms might account for the difference between spectra of Indo-1 measured on intracellular and on extracellular dye. Experiments to discriminate between various possibilities used quantitative analyses of intracellular and extracellular Indo-1 spectra. Intracellular calcium-free dye showed a 20-nm blue shift, when compared with the extracellular case. However, the calcium-bound spectrum was unaffected by the intracellular milieu. This eliminated the possibility that the spectral shift was due to calcium-independent unhydrolyzed dye. The spectral shift was reversible and was seen in resting cells as well as calcium-depleted cells. Since the apparent dissociation constant for calcium was not detectably different inside the cell, the possibility of competitive binding to another divalent cation, such as Zn2+, was eliminated as the principle source of the spectral shift. The shift appears to be due to a noncompetitive solvent effect on the emission of the calcium-free dye that is absent in the calcium-bound form.

Zinc forms complexes with higher kinetical stability than calcium, 5-F-BAPTA as a good example

Increasing interest is focused on the role of zinc in biological systems. A rapidly growing family of DNA-binding proteins contains "zinc-fingers", where zinc is bound to cysteine or histidine residues. On the other hand zinc is able to displace calcium from its binding sites and in this way it may modify calcium-mediated cellular processes. In the present report dissociation rates of Zn2(+)- and Ca2(+)-complexes with 5-F-BAPTA, a widely used NMR-active calcium indicator, have been measured by two-dimensional 19F NMR exchange spectroscopic methods. The results show that the lifetime of the Zn2(+)-complex is more than five times longer than that of the Ca2(+)-complex. The longer lifetime, when combined with a higher thermodynamical stability of the Zn2+-complex, may explain why, in some cellular processes, Zn2+ can compete with Ca2+ in spite of a presumably high [Ca2+]/[Zn2+] free ion concentration ratio.