Hyperekplexia Phenotype of Glycine Receptor α1 Subunit Mutant Mice Identifies Zn2+ as an Essential Endogenous Modulator of Glycinergic Neurotransmission

Abstract

Zn(2+) is thought to modulate neurotransmission by affecting currents mediated by ligand-gated ion channels and transmitter reuptake by Na(+)-dependent transporter systems. Here, we examined the in vivo relevance of Zn(2+) neuromodulation by producing knockin mice carrying the mutation D80A in the glycine receptor (GlyR) alpha1 subunit gene (Glra1). This substitution selectively eliminates the potentiating effect of Zn(2+) on GlyR currents. Mice homozygous for Glra1(D80A) develop a severe neuromotor phenotype postnatally that resembles forms of human hyperekplexia (startle disease) caused by mutations in GlyR genes. In spinal neurons and brainstem slices from Glra1(D80A) mice, GlyR expression, synaptic localization, and basal glycinergic transmission were normal; however, potentiation of spontaneous glycinergic currents by Zn(2+) was significantly impaired. Thus, the hyperekplexia phenotype of Glra1(D80A) mice is due to the loss of Zn(2+) potentiation of alpha1 subunit containing GlyRs, indicating that synaptic Zn(2+) is essential for proper in vivo functioning of glycinergic neurotransmission.

A Novel Dominant Hyperekplexia Mutation Y705C Alters Trafficking and Biochemical Properties of the Presynaptic Glycine Transporter GlyT2

“…10). As expected, we found that Zn 2ϩ sensitivity of wild-type transport was pH-dependent, being higher at pH 7.4 than 5.4, in agreement with the competitive nature of H ϩ and Zn 2ϩ inhibition (35,38,39). By contrast, the inhibition by Zn 2ϩ of the Y705C mutant was much less sensitive to the presence of protons and slightly more pronounced at acidic pH.…”

Supralinear potentiation of NR1/NR3A excitatory glycine receptors by Zn 2+ and NR1 antagonist

“…Release of endogenous Zn 2ϩ in CNS tissue is estimated to raise extracellular Zn 2ϩ concentrations to levels of Ϸ10 M (31). Because 10 M Zn 2ϩ results in a pronounced potentiation of the glycine-induced currents of NR1/NR3A receptors and low micromolar concentrations of this metal ion have been shown to be essential for proper functioning of the inhibitory glycine receptor in vivo (32), the Zn 2ϩ potentiation of NR1/NR3A receptor currents disclosed here may be of physiological importance in vivo. Alternatively, the NR1/NR3A receptor modulation, activation, and supralinear potentiation reactions depicted in Fig.…”

Knock-In Mice Lacking the PDZ-Ligand Motif of mGluR7a Show Impaired PKC-Dependent Autoinhibition of Glutamate Release, Spatial Working Memory Deficits, and Increased Susceptibility to Pentylenetetrazol

“…Positive clones were identified by PCR and confirmed by Southern blot analysis using external and internal probes. Two targeted ES clones were expanded for Cre-mediated deletion in ES cells by transient transfection with a Cre recombinase expression vector as described previously (Hirzel et al, 2006). Neo excision was confirmed by PCR and Southern blotting.…”