Role of P2X4 receptors in synaptic strengthening in mouse CA1 hippocampal neurons

Abstract

P2X4 receptors are calcium-permeable cation channels gated by extracellular ATP. They are found close to subsynaptic sites on hippocampal CA1 neurons. We compared features of synaptic strengthening between wild-type and P2X4 knockout mice (21-26days old). Potentiation evoked by a tetanic presynaptic stimulus (100Hz, 1s) paired with postsynaptic depolarization was less in P2X4 -/- mice than in wild-type mice (230 vs. 50% potentiation). Paired-pulse ratios and the amplitude and frequency of spontaneous excitatory postsynaptic currents (EPSCs) were not different between wild-type and knockout mice. Prior hyperpolarization (ten 3s pulses to -120mV at 0.17Hz) potentiated the amplitude of spontaneous EPSCs in wild-type mice, but not in P2X4 -/- mice; this potentiation was not affected by nifedipine, but was abolished by 10mm 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetra-acetic acid (BAPTA) in the recording pipette. The amplitude of N-methyl-d-aspartate EPSCs (in 6-cyano-7-nitroquinoxaline-2,3-dione, 10 or 30μm, at -100mV) facilitated during 20min recording in magnesium-free solution. In wild-type mice, this facilitation of the N-methyl-d-aspartate EPSC was reduced by about 50% by intracellular BAPTA (10mm), ifenprodil (3μm) or 4-(4-fluorophenyl)-2-(4-methylsulphinylphenyl)-5-(4-pyridyl)1H-imidazole (5μm). In P2X4 -/- mice, the facilitation was much less, and was unaffected by intracellular BAPTA, ifenprodil (3μm) or mitogen-activated protein (MAP) kinase inhibitor 4-(4-fluorophenyl)-2-(4-methylsulphinylphenyl)-5-(4-pyridyl)1H-imidazole (5μm). This suggests that the absence of P2X4 receptors limits the incorporation of NR2B subunits into synaptic N-methyl-d-aspartate receptors. © 2011 The Authors. European Journal of Neuroscience © 2011 Federation of European Neuroscience Societies and Blackwell Publishing Ltd.