Zinc modulation of glycine receptors

doi:10.1016/j.neuroscience.2011.04.021

Neuroscience

Volume 186, 14 July 2011, Pages 32-38

https://doi.org/10.1016/j.neuroscience.2011.04.021 Get rights and content

Abstract

Glycine receptors are widely expressed in the mammalian central nervous system, and previous studies have demonstrated that glycine receptors are modulated by endogenous zinc. Zinc is concentrated in synaptic vesicles in several brain regions but is particularly abundant in the hippocampus and olfactory bulb. In the present study, we used patch-clamp electrophysiology of rat hippocampal and olfactory bulb neurons in primary culture to examine the effects of zinc on glycine receptors. Although glycine has been reported to reach millimolar concentrations during synaptic transmission, most previous studies on the effects of zinc on glycine receptors have used relatively low concentrations of glycine. High concentrations of glycine cause receptor desensitization. Our current results extend our previous demonstration that the modulatory actions of zinc are largely prevented when co-applied with desensitizing concentrations of glycine (300 μM), suggesting that the effects of zinc are dependent on the state of the receptor. In contrast, pre-application of 300 μM zinc, prior to glycine (300 μM) application, causes a slowly developing inhibition with a slow rate of recovery, suggesting that the timing of zinc and glycine release also influences the effects of zinc. Furthermore, previous evidence suggests that synaptically released zinc can gain intracellular access, and we provide the first demonstration that low concentrations of intracellular zinc can potentiate glycine receptors. These results support the notion that zinc has complex effects on glycine receptors and multiple factors may interact to influence the efficacy of glycinergic transmission.

Highlights

▶Modulation of glycine receptors by zinc is dependent on the state of the receptor. ▶The timing of zinc and glycine application influences the effects of zinc. ▶Low concentrations of intracellular zinc potentiate glycine receptors.

Section snippets

Animal use

The animals used for these experiments were used according to the guidelines of our protocol approved by Florida State University's Animal Care and Use Committee and the National Institutes of Health Guide for the Care and Use of Laboratory Animals (NIH Publications No. 80-23).

Tissue culture and electrophysiology

OB and hippocampal neurons from P1 to P5 Sprague-Dawley (Charles River Laboratories International, Inc., Wilmington, MA, USA) rat pups were dissociated and then plated on a confluent layer of astrocytes using standard

Zinc produces biphasic effects on glycine-evoked currents

In both OB and hippocampal neurons, low concentrations of glycine (30 μM) produced membrane currents with little desensitization during 5–10 s applications. Co-application of zinc at 30 μM resulted in potentiation of the current (210±45% of control, n=12) in both neuronal populations (Fig. 1A). Higher concentrations of zinc (e.g. 300 μM) inhibited 30 μM glycine-evoked currents (5.3±6.2% of control, n=10) in both OB and hippocampal neurons (Fig. 1B).

Desensitizing concentrations of glycine block zinc's effects on glycine receptors

In contrast to the above effects of zinc, when

Discussion

The present study extends our previous findings (Trombley and Shepherd, 1996) and provides evidence supporting the notion that the modulatory effects of zinc on glycine receptors depend on the state of the receptor. That is, zinc has little to no effect on glycine-evoked currents when co-applied during receptor desensitization. Furthermore, this report is the first to provide evidence for the existence of an intracellular modulatory effect of zinc on glycine receptors.

Acknowledgments

This work was supported, in part, by NIH/NIDCD and a grant from the Florida State University Council on Research and Creativity.

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We also showed that patterned (sniff frequency) stimulation of the olfactory nerve causes OSN terminals to release vesicular zinc (Blakemore et al., 2013), providing further evidence that zinc is released in response to neuronal activity, and thus, is available to modulate synaptic transmission in the OB. Modulation of amino acid receptors (e.g., AMPA, NMDA, GABA, glycine) and synaptic transmission by zinc is well described (Smart et al., 1994; Bitanihirwe and Cunningham, 2009; Nakashima and Dyck, 2009; Paoletti et al., 2009; Blakemore and Trombley, 2017; McAllister and Dyck, 2017), including that demonstrated by us in the OB (Trombley and Shepherd, 1996; Trombley et al., 1998; Blakemore and Trombley, 2004; Trombley et al., 2011; Blakemore et al., 2013; Blakemore and Trombley, 2019). However, relatively little is known about effects of zinc on isolated KARs.
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Cellular and Molecular NeuroscienceResearch PaperZinc modulation of glycine receptors

Abstract

Highlights

Section snippets

Animal use

Tissue culture and electrophysiology

Zinc produces biphasic effects on glycine-evoked currents

Desensitizing concentrations of glycine block zinc's effects on glycine receptors

Discussion

Acknowledgments

Int Rev Neurobiol

Neuropharmacology

Neuroscience

Trends Pharmacol Sci

J Biol Chem

Brain Res Rev

J Biol Chem

Neuroscience

Neurosci Lett

Brain Res

Release of endogenous Zn2+ from brain tissue during activity

Nature

A proton-dependent zinc uptake in PC12 cells

Neurochem Res

The time course of transmitter at glycinergic synapses onto motoneurons

J Neurosci

Zinc co-localizes with GABA and glycine in synapses in the lamprey spinal cord

J Comp Neurol

Diverse modulation of olfactory bulb AMPA receptors by zinc

Neuroreport

Biphasic modulation of the strychnine-sensitive glycine receptor by Zn2+

Mol Pharmacol

Cellular and Molecular Neuroscience
Research Paper
Zinc modulation of glycine receptors

Release of endogenous Zn²⁺ from brain tissue during activity

Biphasic modulation of the strychnine-sensitive glycine receptor by Zn²⁺