Tobramycin/Edetate Calcium sodium

A recent study investigated the impact of glutathione (GSH) on the transfer of zinc (Zn) from proteome to apo-carbonic anhydrase. Here, we probed the requirement of glutathione for zinc trafficking in LLC-PK1 pig kidney epithelial cells. Depletion of GSH by at least 95% left cells viable and able to divide and synthesize Zn-proteins at the control rate over a 48-h period. Loss of GSH stimulated the accumulation of 2.5x the normal concentration of cellular Zn. According to gel filtration chromatography, differential centrifugal filtration, and spectrofluorimetry with TSQ, the extra Zn was distributed between the proteome and metallothionein (MT). To test the functionality of proteome and/or MT as sources of Zn for the constitution of Zn-proteins, GSH-deficient cells were incubated with CaEDTA to isolate them from their normal source of nutrient Zn. Control cells plus CaEDTA stopped dividing; GSH-depleted cells plus CaEDTA continued to divide at ∼40% the rate of GSH deficient cells. Evidently, proteome and/or MT served as a functional source of Zn for generating Zn-proteins. In vitro insertion of Zn bound to proteome into apo-carbonic anhydrase occurred faster at larger concentrations of Zn bound to proteome. These results support the hypothesis that enhanced transport of Zn into cells drives the conversion of apo-Zn-proteins to Zn-proteins by mass action. Similar results were also obtained with human Jurkat T lymphocyte epithelial cells. This study reveals a powerful new model for studying the chemistry of Zn trafficking, including transport processes, involvement of intermediate binding sites, and constitution of Zn-proteins.

Beta-adrenergic receptors in the basolateral amygdala play an essential role in fear memory, while the physiological role of intracellular Zn²⁺ remains to be clarified. Intracellular Zn²⁺ level was decreased 5 min after local injection of 500 μM isoproterenol (2 μl), a nonselective beta-adrenergic receptor agonist into the basolateral amygdala, suggesting that intracellular Zn²⁺ dynamic is linked with beta-adrenergic receptor signaling in the basolateral amygdala. When isoproterenol was injected into the basolateral amygdala 20 min prior to long-term potentiation (LTP) induction, LTP at perforant pathway-basolateral amygdala was enhanced and conditioned fear memory was also augmented, suggesting that isoproterenol leads to utilization of Zn²⁺ to consolidate fear memory followed by lowering intracellular Zn²⁺. We postulated that synaptic Zn²⁺ dynamics under conditioned fear experience regulates conditioned fear memory in cooperation with beta-adrenergic receptor signaling. When either intracellular Zn²⁺ chelator (ZnAF-2DA) or extracellular Zn²⁺ chelator (CaEDTA) was locally injected into the basolateral amygdala in the same manner, LTP was also enhanced. The local injection of ZnAF-2DA augmented fear memory. It is likely that the decrease in availability of intracellular Zn²⁺ by Zn²⁺ chelators under fear experience affects the function of Zn²⁺-required proteins followed by augmentation of fear memory and its related LTP. The present study suggests that beta-adrenergic receptor signaling is linked with intracellular Zn²⁺ signaling in the basolateral amygdala to consolidate conditioned fear memory. Because intracellular Zn²⁺ signaling is required for fear memory, the decrease in availability of intracellular Zn²⁺ may augment fear memory and its related LTP under non-physiological condition.