Up-regulation of Cavβ3 Subunit in Primary Sensory Neurons Increases Voltage-activated Ca2+ Channel Activity and Nociceptive Input in Neuropathic Pain

et al. 2014

Molecular Pharmacology

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4-Aminopyridine (4-AP, fampridine) is used clinically to improve neuromuscular function in patients with multiple sclerosis, spinal cord injury, and myasthenia gravis. 4-AP can increase neuromuscular and synaptic transmission by directly stimulating high voltageactivated (HVA) Ca 21 channels independent of its blocking effect on voltage-activated K 1 channels. Here we provide new evidence that the potentiating effect of 4-AP on HVA Ca 21 channels depends on the specific combination of voltage-activated calcium channel a1 (Cava 1 ) and voltage-activated calcium channel b (Cavb) subunits. Among the four Cavb subunits examined, Cavb3 was the most significant subunit involved in the 4-AP-induced potentiation of both L-type and N-type currents. Of particular note, 4-AP at micromolar concentrations selectively potentiated L-type currents reconstituted with Cav1.2, a 2 d1, and Cavb3. In contrast, 4-AP potentiated N-type currents only at much higher concentrations and had little effect on P/Q-type currents. In a phrenic nerve-diaphragm preparation, blocking L-type Ca 21 channels eliminated the potentiating effect of low concentrations of 4-AP on end-plate potentials. Furthermore, 4-AP enhanced the physical interaction of Cav1.2 and Cav2.2 subunits to Cavb3 and also increased their trafficking to the plasma membrane. Site-directed mutagenesis identified specific regions in the guanylate kinase, HOOK, and C-terminus domains of the Cavb3 subunit crucial to the ability of 4-AP to potentiate L-type and N-type currents. Our findings indicate that 4-AP potentiates HVA Ca 21 channels by enhancing reciprocal Cav1.2-Cavb3 and Cav2.2-Cavb3 interactions. The therapeutic effect of 4-AP on neuromuscular function is probably mediated by its actions on Cavb3-containing L-type Ca 21 channels.

Section: Ca 21 Channel Subunits and 4-aminopyridine Actionsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Potentiation of High Voltage–Activated Calcium Channels by 4-Aminopyridine Depends on Subunit Composition

et al. 2014

Molecular Pharmacology

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“…Nerve injury can increase the excitability of DRG neurons and increase Ca 21 influx and Ca 21 -mediated signaling to increase calcineurin activity in DRG neurons (Ma and LaMotte, 2005;Wu et al, 2005Wu et al, , 2006Li et al, 2012). In the DRG and spinal cord, NFATc regulates the expression of several pronociceptive and proinflammatory genes, including cyclooxygenase-2, nerve growth factor, interleukin-1, and C-C chemokine receptor type 2 (CCR2) (Iniguez et al, 2000;Marchand et al, 2005;Groth et al, 2007;White et al, 2007;Flockhart et al, 2008).…”

Section: Introductionmentioning

confidence: 99%

Upregulation of Nuclear Factor of Activated T-Cells by Nerve Injury Contributes to Development of Neuropathic Pain

Cai

Pan

2013

J Pharmacol Exp Ther

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Nerve injury induces long-term changes in gene expression in the nociceptive circuitry and can lead to chronic neuropathic pain. However, the transcriptional mechanism involved in neuropathic pain is poorly understood. Nuclear factor of activated T-cells (NFATc) is a transcriptional factor regulated by the Ca 21 -dependent protein phosphatase calcineurin. In this study, we determined nerve injury-induced changes in the expression of NFATc1-c4 in the dorsal root ganglia (DRG) and spinal cords and their role in the development of neuropathic pain. The mRNA of NFATc1-c4 was detected in the rat DRG and dorsal spinal cord. Nerve injury transiently elevated NFATc1-c3 mRNA levels and persistently increased NFATc4 and C-C chemokine receptor type 2 (CCR2) mRNA levels in the DRG. However, NFATc1-c4 mRNA levels in the spinal cord were not altered significantly by nerve injury. Nerve injury also significantly increased the protein level of dephosphorylated NFATc4 in the DRG. Intrathecal injection of the specific NFATc inhibitor 11R-VIVIT or the calcineurin inhibitor FK-506 (tacrolimus) early after nerve injury significantly attenuated the development of tactile allodynia. In addition, treatment with FK-506 or 11R-VIVIT significantly reduced the mRNA levels of NFATc4 and CCR2 but not large-conductance Ca 21 -activated K 1 channels, in the DRG after nerve injury. Our findings suggest that peripheral nerve injury causes a time-dependent change in NFATc1-c4 expression in the DRG. CalcineurinNFATc-mediated expression of pronociceptive cytokines contributes to the transition from acute to chronic pain after nerve injury.

“…Both peripheral sensitization at the injury site and hyperactivity of the spinal dorsal horn neurons result in pain hypersensitivity after nerve injury (Campbell et al, 1988;Gracely et al, 1992). Increased glutamatergic synaptic input to spinal dorsal horn neurons plays a critical role in the development of central sensitization and neuropathic pain (Chaplan et al, 1997;Wang et al, 2007;Zhou et al, 2011a;Li et al, 2012b). In addition, increased N-methyl-D-aspartate receptor (NMDAR) activity by nerve injury diminishes normal synaptic inhibition mediated by GABA and glycine in the spinal cord through increased proteolysis of K 1 -Cl 2 cotransporter-2 mediated by calpain (Zhou et al, 2012).…”

Section: Introductionmentioning

confidence: 99%

Casein Kinase II RegulatesN-Methyl-d-Aspartate Receptor Activity in Spinal Cords and Pain Hypersensitivity Induced by Nerve Injury

Zhou

Byun

et al. 2014

J Pharmacol Exp Ther

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Increased N-methyl-D-aspartate receptor (NMDAR) activity and phosphorylation in the spinal cord are critically involved in the synaptic plasticity and central sensitization associated with neuropathic pain. However, the mechanisms underlying increased NMDAR activity in neuropathic pain conditions remain poorly understood. Here we show that peripheral nerve injury induces a large GluN2A-mediated increase in NMDAR activity in spinal lamina II, but not lamina I, neurons. However, NMDAR currents in spinal dorsal horn neurons are not significantly altered in rat models of diabetic neuropathic pain and resiniferatoxin-induced painful neuropathy (postherpedic neuralgia). Inhibition of protein tyrosine kinases or protein kinase C has little effect on NMDAR currents potentiated by nerve injury. Strikingly, casein kinase II (CK2) inhibitors normalize increased NMDAR currents of dorsal horn neurons in nerve-injured rats. In addition, inhibition of calcineurin, but not protein phosphatase 1/2A, augments NMDAR currents only in control rats. CK2 inhibition blocks the increase in spinal NMDAR activity by the calcineurin inhibitor in control rats. Furthermore, nerve injury significantly increases CK2a and CK2b protein levels in the spinal cord. In addition, inhibition of CK2 or CK2b knockdown at the spinal level substantially reverses pain hypersensitivity induced by nerve injury. Our study indicates that neuropathic pain conditions with different etiologies do not share the same mechanisms, and increased spinal NMDAR activity is distinctly associated with traumatic nerve injury. CK2 plays a prominent role in the potentiation of NMDAR activity in the spinal dorsal horn and may represent a new target for treatments of chronic pain caused by nerve injury.