ABSTRACT
Ionic zinc is found at a high concentration in some glutamatergic vesicles of the mammalian brain. Ionic zinc is also found chelated to macromolecules in the extracellular space, constituting what has been called the "zinc veneer". In this communication we show that the zinc ionophore, pyrithione, can be used to demonstrate the presence of the veneer. Application of pyrithione without added ionic zinc to rodent hippocampal slices mobilizes extracellular zinc, which can be detected intracellularly by the zinc probe FluoZin-3. In addition, we show that ZnT3 null mice, which lack the transporter responsible for stocking synaptic vesicles, nevertheless do have a zinc veneer, albeit diminished compared to wild type animals. The presence of the zinc veneer in ZnT3 null mice may account for the absence of any marked deficit in these animals.
Subject(s)
Brain/metabolism , Extracellular Fluid/metabolism , Ionophores/metabolism , Membrane Proteins/deficiency , Polycyclic Compounds/metabolism , Zinc/metabolism , Animals , Carrier Proteins/analysis , Cation Transport Proteins , Ionophores/analysis , Male , Membrane Proteins/analysis , Membrane Transport Proteins , Mice , Mice, Knockout , Organ Culture Techniques , Polycyclic Compounds/analysis , Rats , Rats, Sprague-Dawley , Zinc/analysisABSTRACT
The synaptic vesicles of some glutamatergic terminals contain a high concentration of zinc that serves functions that remain obscure. In this publication we have used the membrane permeant zinc fluophore, ZnAF-2 to determine if zinc is released during the course of synaptic transmission. Stimulation of the slices with either high potassium or electrically, leads to an increase in fluorescence that long outlasts the stimulus and remains elevated for many minutes. We demonstrate that this response is inconsistent with the free release of zinc but is with the presentation of zinc coordinated to macromolecules within the exocytosed vesicles to the extracellular space; a process we term 'externalization'. Our data suggests a novel mechanism of synaptic transmission at zinc-rich glutamatergic terminals that distinguishes them from their metal free counterparts.
ABSTRACT
Inorganic phosphate (Pi) is an important polyanion needed for ATP synthesis and bone formation. As it is found at millimolar levels in plasma, it is usually incorporated as a constituent of artificial CSF formulations for maintaining brain slices. In this paper, we show that Pi limits the extracellular zinc concentration by inducing metal precipitation. We present data suggesting that amino acids like histidine may counteract the Pi-induced zinc precipitation by the formation of soluble zinc complexes. We propose that the interplay between Pi and amino acids in the extracellular space may influence the availability of metals for cellular uptake.