Allosteric Modulation of Ca2+ flux in Ligand-gated Cation Channel (P2X4) by Actions on Lateral Portals

• Published in: The Journal of biological chemistry 2012-03, Vol.287 (10), p.7594-7602
• Main Authors: Samways, Damien S.K., Khakh, Baljit S., Egan, Terrance M.
• Format: Article
• Language: English
• Subjects: Allosteric Regulation - drug effects; Allosteric Regulation - genetics; Amino Acid Substitution; Antiparasitic Agents - pharmacology; ATP; Calcium - metabolism; Calcium Signaling; Cell Line, Transformed; Fenestration; Fractional Calcium Current; Humans; Ion Channel Gating; Ion Channels; Ion Transport - drug effects; Ion Transport - genetics; Ivermectin; Ivermectin - pharmacology; Microglia; Microglia - metabolism; Microglia - pathology; Molecular Biophysics; Mutation, Missense; Nerve Tissue Proteins - genetics; Nerve Tissue Proteins - metabolism; Neuralgia - drug therapy; Neuralgia - metabolism; Neuralgia - pathology; Pf; Purinergic Receptor; Receptors, Purinergic P2X4 - genetics; Receptors, Purinergic P2X4 - metabolism; Signal Transduction - drug effects; Signal Transduction - genetics
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M111.322461

Human P2X receptors are a family of seven ATP-gated ion channels that transport Na+, K+, and Ca2+ across cell surface membranes. The P2X4 receptor is unique among family members in its sensitivity to the macrocyclic lactone, ivermectin, which allosterically modulates both ion conduction and channel gating. In this paper we show that removing the fixed negative charge of a single acidic amino acid (Glu51) in the lateral entrance to the transmembrane pore markedly attenuates the effect of ivermectin on Ca2+ current and channel gating. Ca2+ entry through P2X4 receptors is known to trigger downstream signaling pathways in microglia. Our experiments show that the lateral portals could present a novel target for drugs in the treatment of microglia-associated disease including neuropathic pain. Ca2+ currents of ligand-gated ion channels are essential to cell signaling. We show that the Ca2+ currents of P2X4 channels are subject to allosteric modulation. The fixed negative charge of a single amino acid is required for the allosteric effects of ivermectin on permeability, flux, and current deactivation. Allosteric modulators may provide therapeutic relief from symptoms of diseases such as peripheral neuropathy and hypertension.