CCR2 Receptor Ligands Inhibit Cav3.2 T-Type Calcium Channels

Haitao You,Gerald W Zamponi,Christophe Altier

doi:10.1124/mol.109.059022

Abstract

Monocyte chemoattractant protein-1 (MCP-1) is a cytokine known to be involved in the recruitment of monocytes to sites of injury. MCP-1 activates the chemokine (C-C motif) receptor 2 (CCR2), a seven-transmembrane helix G protein-coupled receptor that has been implicated in inflammatory pain responses. Here we show that MCP-1 mediates activation of the CCR2 receptor and inhibits coexpressed N-type calcium channels in tsA-201 cells via a voltage-dependent pathway. Moreover, MCP-1 inhibits Ca(v)3.2 calcium channels, but not other members of the Cav3 calcium channel family, with nanomolar affinity. Unlike in N-type channels, this modulation does not require CCR2 receptor activation and seems to involve a direct action of the ligand on the channel. Whole-cell T-type calcium currents in acutely dissociated dorsal root ganglia neurons are effectively inhibited by MCP-1, consistent with the notion that these cells express Ca(v)3.2. The effects of MCP-1 were eliminated by heat denaturation. Furthermore, they were sensitive to the application of the divalent metal ion chelator diethylenetriaminepentaacetic acid, suggesting the possibility that metal ions may act as a cofactor. Finally, small organic CCR2 receptor antagonists inhibit Ca(v)3.2 and other members of the T-type channel family with micromolar affinity. Our findings provide novel avenues for the design of small organic inhibitors of T-type calcium channels for the treatment of pain and other T-type channel linked disorders.

Highlights

Besides direct block by peptidergic or small organic calcium-channel blockers, voltage-gated calcium channels can be inhibited by activation of certain types of G protein-coupled receptors, such as ␮-opioid receptors, which reduce N-type calcium channel activity via a voltage-dependent pathway that involves binding of G␤␥ subunits to the channel protein
The exact opposite is the case as monocyte chemoattractant protein-1 (MCP-1) inhibits N-type calcium channels via a G protein-coupled pathway, whereas T-type calcium channels of the Cav3.2 subtype are inhibited directly and with high affinity through a receptorindependent pathway
To rule out expression system artifacts and to determine whether native Cav3.2 channels are subject to MCP-1inhibition, we examined the effects of MCP-1 on native T-type currents in acutely dissociated rat Dorsal root ganglion (DRG) neurons

Summary

Introduction

Its release may increase the excitability of surrounding neurons within the dorsal root ganglia, thereby resulting in proalgesia (White et al, 2007) This may be further exacerbated by release of MCP-1 from nerve terminals of primary afferent fibers, which has been shown to activate microglia in the spinal cord (Zhang et al, 2007; Thacker et al, 2009). Intrathecal administration of CCR2 receptor antagonists alleviates neuropathic pain (Dansereau et al, 2008; Abbadie et al, 2009). Given these proalgesic actions of MCP-1, we wondered whether they might in part arise from an enhancement of activation of N- or T-type calcium channel activity. Cav3.2 channels can be inhibited by CCR2 receptor antagonists, which could serve as initial structural scaffolds for the development of higher affinity T-type channel blockers

Methods

Results

Conclusion