Functional properties of internalization-deficient P2X4 receptors reveal a novel mechanism of ligand-gated channel facilitation by ivermectin.
Molecular Pharmacology. 2005-11-17; 69(2): 576-587
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1. Mol Pharmacol. 2006 Feb;69(2):576-87. Epub 2005 Nov 10.
Functional properties of internalization-deficient P2X4 receptors reveal a novel
mechanism of ligand-gated channel facilitation by ivermectin.
Toulmé E(1), Soto F, Garret M, Boué-Grabot E.
(1)Centre National de la Recherche Scientifique Unité Mixte de Recherche 5543,
Université Victor Segalen Bordeaux2, France.
Although P2X receptors within the central nervous system mediate excitatory ATP
synaptic transmission, the identity of central ATP-gated channels has not yet
been elucidated. P2X(4), the most widely expressed subunit in the brain, was
previously shown to undergo clathrin-dependent constitutive internalization by
direct interaction between activator protein (AP)2 adaptors and a tyrosine-based
sorting signal specifically present in the cytosolic C-terminal tail of mammalian
P2X(4) sequences. In this study, we first used internalization-deficient P2X(4)
receptor mutants to show that suppression of the endocytosis motif significantly
increased the apparent sensitivity to ATP and the ionic permeability of P2X(4)
channels. These unique properties, observed at low channel density, suggest that
interactions with AP2 complexes may modulate the function of P2X(4) receptors. In
addition, ivermectin, an allosteric modulator of several receptor channels,
including mammalian P2X(4), did not potentiate the maximal current of
internalization-deficient rat or human P2X(4) receptors. We demonstrated that
binding of ivermectin onto wild-type P2X(4) channels increased the fraction of
plasma membrane P2X(4) receptors, whereas surface expression of
internalization-deficient P2X(4) receptors remained unchanged. Disruption of the
clathrin-mediated endocytosis with the dominant-negative mutants Eps15 or AP-50
abolished the ivermectin potentiation of wild-type P2X(4) channel currents.
Likewise, ivermectin increased the membrane fraction of nicotinic alpha7
acetylcholine (nalpha7ACh) receptors and the potentiation of acetylcholine
current by ivermectin was suppressed when the same dominant-negative mutants were
expressed. These data showed that potentiation by ivermectin of both P2X(4) and
nalpha7ACh receptors was primarily caused by an increase in the number of cell
surface receptors resulting from a mechanism dependent on clathrin/AP2-mediated
PMID: 16282518 [Indexed for MEDLINE]