Pharmacological disruption of calcium channel trafficking by the 2 ligand gabapentin

Laboratory for Cellular and Molecular Neuroscience, Department of Pharmacology, University College London, London WC1E 6BT, United Kingdom.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 04/2008; 105(9):3628-33. DOI: 10.1073/pnas.0708930105
Source: PubMed


The mechanism of action of the antiepileptic and antinociceptive drugs of the gabapentinoid family has remained poorly understood. Gabapentin (GBP) binds to an exofacial epitope of the alpha(2)delta-1 and alpha(2)delta-2 auxiliary subunits of voltage-gated calcium channels, but acute inhibition of calcium currents by GBP is either very minor or absent. We formulated the hypothesis that GBP impairs the ability of alpha(2)delta subunits to enhance voltage-gated Ca(2+)channel plasma membrane density by means of an effect on trafficking. Our results conclusively demonstrate that GBP inhibits calcium currents, mimicking a lack of alpha(2)delta only when applied chronically, but not acutely, both in heterologous expression systems and in dorsal root-ganglion neurons. GBP acts primarily at an intracellular location, requiring uptake, because the effect of chronically applied GBP is blocked by an inhibitor of the system-L neutral amino acid transporters and enhanced by coexpression of a transporter. However, it is mediated by alpha(2)delta subunits, being prevented by mutations in either alpha(2)delta-1 or alpha(2)delta-2 that abolish GBP binding, and is not observed for alpha(2)delta-3, which does not bind GBP. Furthermore, the trafficking of alpha(2)delta-2 and Ca(V)2 channels is disrupted both by GBP and by the mutation in alpha(2)delta-2, which prevents GBP binding, and we find that GBP reduces cell-surface expression of alpha(2)delta-2 and Ca(V)2.1 subunits. Our evidence indicates that GBP may act chronically by displacing an endogenous ligand that is normally a positive modulator of alpha(2)delta subunit function, thereby impairing the trafficking function of the alpha(2)delta subunits to which it binds.

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    • "These compounds are useful in the treatment of a number of disorders, including epilepsy, but their modes of action are nonselective , and therefore, conclusions regarding the effects on GABA, particularly synaptic, are difficult to draw. The activity of these anticonvulsants include, but are not limited to, sodium and calcium channel modulation, mitochondrial neuroprotection, manipulation of the equilibrium with other neurotransmitters , and enzymatic induction or inhibition (Hendrich et al., 2008; Kudin et al., 2004; Micheva et al., 2006; Petroff et al., 1999a; Rogawski, 2006). More selective compounds, which modulate GABA directly, provide more pertinent tests of MRS sensitivity . "
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    ABSTRACT: Though GABA is the major inhibitory neurotransmitter in the brain, involved in a wide variety of brain functions and many neuropsychiatric disorders, its intracellular and metabolic presence provides uncertainty in the interpretation of the GABA signal measured by 1H-MRS. Previous studies demonstrating the sensitivity of this technique to pharmacological manipulations of GABA have used non-specific challenges that make it difficult to infer the exact source of the changes. In this study, the synaptic GABA reuptake inhibitor tiagabine, which selectively blocks GAT1, was used to test the sensitivity of J-difference edited 1H-MRS to changes in extracellular GABA concentrations.MEGA-PRESS was used to obtain GABA-edited spectra in 10 male individuals, before and after a 15 mg oral dose of tiagabine. In the three voxels measured, no significant changes were found in GABA+ concentration after the challenge compared to baseline. This dose of tiagabine is known to modulate synaptic GABA and neurotransmission through studies using other imaging modalities, and significant increases in self-reported sleepiness scales were observed. Therefore it is concluded that recompartmentalisation of GABA through transport block does not have a significant impact on total GABA concentration. Furthermore, it is likely that the majority of the MRS-derived GABA signal is intracellular. It should be considered, in individual interpretation of GABA MRS studies, whether it is appropriate to attribute observed effects to changes in neurotransmission. Synapse, 2014. © 2014 Wiley Periodicals, Inc.
    Synapse 08/2014; 68(8). DOI:10.1002/syn.21747 · 2.13 Impact Factor
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    • "These findings fit nicely with previous studies showing that the GABA-like antiepileptic drugs Gabapentin and Pregabalin bind α 2 δ-1 and α 2 δ-2 (Gee et al., 1996; Wang et al., 1999; Bian et al., 2006; Field et al., 2006). Although some reports indicate that these drugs produce acute inhibition of calcium currents (Stefani et al., 1998; Martin et al., 2002), the prevailing view is that the pharmacological action involves inhibition of the forward trafficking of Ca V 2.1 and Ca V 2.2 following chronic exposure (Kang et al., 2002; Vega-Hernandez and Felix, 2002; Hendrich et al., 2008). Binding of Gabapentin to α 2 δ appears to disrupt Rab11-dependent recycling from late endosomes, preventing the channel complex from returning to the plasma membrane (Tran-Van-Minh and Dolphin, 2010). "
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    ABSTRACT: Openings of high-voltage-activated (HVA) calcium channels lead to a transient increase in calcium concentration that in turn activate a plethora of cellular functions, including muscle contraction, secretion and gene transcription. To coordinate all these responses calcium channels form supramolecular assemblies containing effectors and regulatory proteins that couple calcium influx to the downstream signal cascades and to feedback elements. According to the original biochemical characterization of skeletal muscle Dihydropyridine receptors, HVA calcium channels are multi-subunit protein complexes consisting of a pore-forming subunit (α1) associated with four additional polypeptide chains β, α2, δ, and γ, often referred to as accessory subunits. Twenty-five years after the first purification of a high-voltage calcium channel, the concept of a flexible stoichiometry to expand the repertoire of mechanisms that regulate calcium channel influx has emerged. Several other proteins have been identified that associate directly with the α1-subunit, including calmodulin and multiple members of the small and large GTPase family. Some of these proteins only interact with a subset of α1-subunits and during specific stages of biogenesis. More strikingly, most of the α1-subunit interacting proteins, such as the β-subunit and small GTPases, regulate both gating and trafficking through a variety of mechanisms. Modulation of channel activity covers almost all biophysical properties of the channel. Likewise, regulation of the number of channels in the plasma membrane is performed by altering the release of the α1-subunit from the endoplasmic reticulum, by reducing its degradation or enhancing its recycling back to the cell surface. In this review, we discuss the structural basis, interplay and functional role of selected proteins that interact with the central pore-forming subunit of HVA calcium channels.
    Frontiers in Physiology 06/2014; 5:209. DOI:10.3389/fphys.2014.00209 · 3.53 Impact Factor
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    • "It is likely that in neurons a 2 d subunits have multiple effects on calcium channel distribution, both associated with long-range calcium channel trafficking from their site of synthesis in the soma to their mainly presynaptic localization in nerve terminals (Bauer et al., 2009), and also local effects on calcium channel localization in membrane micro-domains such as the active zone and in lipid rafts (Davies et al., 2006; Hoppa et al., 2012), as well as influencing the recycling of calcium channels to the plasma membrane (Tran-Van- Minh and Dolphin, 2010). Furthermore, we have found that the gabapentinoid drugs have an inhibitory effect on calcium currents when applied over longer time periods, in cultured cells and neurons (Hendrich et al., 2008; Tran-Van-Minh and Dolphin, 2010), which we infer is by inhibiting the trafficking of the a 2 d subunits (Hendrich et al., 2008; Bauer et al., 2010; Tran-Van-Minh and Dolphin, 2010). We also observed in vivo that there was less upregulation of a 2 d-1 in nerve terminal zones, after the induction of somatosensory nerve injury when it was combined with chronic pregabalin treatment (Bauer et al., 2009), which might be an effect on long range axonal trafficking, or on lifetime of the protein and its local recycling at presynaptic terminals. "
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    ABSTRACT: The auxiliary α2δ-1 subunit of voltage-gated calcium channels is up-regulated in dorsal root ganglion neurons following peripheral somatosensory nerve damage, in several animal models of neuropathic pain. The α2δ-1 protein has a mainly presynaptic localization, where it is associated with the calcium channels involved in neurotransmitter release. Relevant to the present study, α2δ-1 has been shown to be the therapeutic target of the gabapentinoid drugs in their alleviation of neuropathic pain. These drugs are also used in the treatment of certain epilepsies. In this study we therefore examined whether the level or distribution of α2δ-1 was altered in the hippocampus following experimental induction of epileptic seizures in rats, using both the kainic acid model of human temporal lobe epilepsy, in which status epilepticus is induced, and the tetanus toxin model in which status epilepticus is not involved. The main finding of this study is that we did not identify somatic overexpression of α2δ-1 in hippocampal neurons in either of the epilepsy models, unlike the upregulation of α2δ-1 that occurs following peripheral nerve damage to both somatosensory and motor neurons. However, we did observe local reorganisation of α2δ-1 immunostaining in the hippocampus only in the kainic acid model, where it was associated with areas of neuronal cell loss, as indicated by absence of NeuN immunostaining, dendritic loss, as identified by areas where microtubule-associated protein-2 immunostaining was missing, and reactive gliosis, determined by regions of strong OX42 staining.
    Neuroscience 03/2014; 283. DOI:10.1016/j.neuroscience.2014.03.013 · 3.36 Impact Factor
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