ATP P_2XReceptors Mediate Fast Synaptic Transmission in the Dorsal Horn of the Rat Spinal Cord

Abstract

ATP has been proposed to mediate synaptic transmission in the spinal cord dorsal horn, particularly in the pathway carrying nociceptive information. Using transverse spinal cord slices from postnatal rats, we show that EPSCs mediated by P 2X receptors, and presumably activated by synaptically released ATP, are evoked in a subpopulation of spinal cord lamina II neurons, a region known to receive strong input from nociceptive primary afferents. The P 2X receptors on acutely dissociated dorsal horn neurons are nondesensitizing, insensitive to ␣␤ methylene ATP, and show strong but variable sensitivity to the antagonists suramin and pyridoxal-phosphate-6-azophenyl-2Ј,4Ј-disulfonic acid (PPADS). These characteristics are consistent with a heterogeneous population of P 2X receptors, the composition of which includes P 2X2 , P 2X4 , and P 2X6 receptor subtypes. Our results suggest that ATP-activated P 2X receptors in lamina II of the rat spinal cord may play a role in transmitting or modulating nociceptive information. Holton and Holton (1954) first proposed ATP as a possible neurotransmitter in the dorsal horn over 40 years ago. Since then, its role as a fast neurotransmitter in the peripheral nervous system has been demonstrated (Burnstock et al., 1972;Evans et al., 1992;Silinsky and Gerzanich, 1993;Galligan and Bertrand, 1994). In the C NS only one study, performed on neurons in the medial habenula, has demonstrated that ATP can act as a fast neurotransmitter (Edwards et al., 1992). Within the spinal cord dorsal horn, despite strong evidence implicating ATP as a putative neurotransmitter (Jahr and Jessell, 1983;Fyffe and Perl, 1984;Salter and Henry, 1985;Salter and Hicks, 1994), its role in this regard has not been demonstrated (Li and Perl, 1995).Several ATP receptor subunits have been cloned from different tissues (Brake et al., 1994;Valera et al., 1994;Chen et al., 1995;Lewis et al., 1995;Buell et al., 1996;Collo et al., 1996;Vulchanova et al., 1996). Of those cloned, the ATP P 2X2 , P 2X4 , and P 2X6 receptor subunit RNAs have been shown to be expressed in the spinal cord dorsal horn, particularly in the superficial laminae of the dorsal horn (Brake et al., 1994;Buell et al., 1996;Vulchanova et al., 1996), lending f urther support to the idea that ATP receptors may participate in synaptic function there. Recently, P 2X7 mRNA also was detected in both brain and spinal cord (and elsewhere), but its exact distribution was not described . When P 2X2 , P 2X4 , and P 2X6 receptor subunits are expressed in heterologous cellular systems in homomeric form, they all mediate a nondesensitizing response to ATP and are insensitive to the agonist ␣␤ methylene ATP (Brake et al., 1994;Collo et al., 1996;Séguéla et al., 1996), making them pharmacologically distinguishable from the other P 2X subunits. A further pharmacological distinction among subunits is that, whereas responses mediated by the P 2X2 subunit are sensitive to the antagonists suramin and pyridoxal-phosphate-6-azophenyl-2Ј,4Ј-disulfonic acid (PPADS), P 2X4 and P 2X...

Hetero-oligomeric Assembly of P2X Receptor Subunits

“…Peak currents are normalized to show that the time courses of the ATP-gated currents are not affected by addition of either tag. ATP was applied at a concentration of 30 M for P2X [1][2][3][4][5] and 300 M for P2X 7 . Holding voltage was Ϫ40 mV.…”

“…The P2X receptors are nonselective ion channels thought to be oligomeric in nature, and they are expressed in many excitable and nonexcitable cells, where they mediate a variety of physiological actions, including smooth muscle contractility, neuroendocrine secretion, and modulation of synaptic transmission (2,3). In addition, recent reports suggest that they may also play an important role in the transmission of pain perception (4,5). With the molecular identification of seven P2X receptor subunits, our understanding of the biophysical and pharmacological properties of these channels has been considerably increased.…”

Comparative study of the P2X gene family in animals and plants

“…P2X3 receptors were suggested to be involved in mechanosensory transduction of mice-the base of inflammatory pain [24]. Furthermore, P2X2, P2X4, and P2X7 receptors are expressed in dorsal horn neurons delivering nociceptive information in mice [25]. In addition, other roles of P2X have been identified: P2X7 are associated with inflammation, immunomodulation [26], and apoptosis of cancer cells [27]; P2X4 and P2X1 are involved in cardiovascular diseases in rats and humans [28]; P2X2 and P2X3 are involved in special sense [29,30].…”

Purinergic P2X receptors facilitate inhibitory GABAergic and glycinergic neurotransmission to cardiac vagal neurons in the nucleus ambiguus

“…The purine nucleotide ATP is widely accepted as a neurotransmitter in both the peripheral and central nervous system and has been shown to mediate neurotransmission throughout regions of the brain including the hippocampus (Bardoni et al, 1997), dorsal horn of the spinal cord (Sorimachi et al, 2001)and the hypothalamus (Edwards et al, 1997). ATP can act as an extracellular signaling molecule that mediates ionotropic and metabotropic P2 receptors, P2Y G protein-coupled receptors and P2X ionotropic ligand-gated receptors (North and Barnard, 1997); (Burnstock and Wood, 1996).…”