ABSTRACT
The P2X(3) receptor is an ATP-gated ion channel predominantly expressed in nociceptive neurons from the dorsal root ganglion. P2X(3) receptor channels are highly expressed in sensory neurons and probably contribute to the sensation of pain. Kinetics of P2X(3) currents are characterized by rapid desensitization (<100 ms) and slow recovery (>20 s). Thus, any mechanism modulating rate of desensitization and/or recovery may have profound effect on susceptibility of nociceptive neurons expressing P2X(3) to ATP. Here we show that currents mediated by P2X(3) receptor channels and the heteromeric channel P2X(2/3) composed of P2X(2) and P2X(3) subunits are potentiated by the neuropeptides substance P and bradykinin, which are known to modulate pain perception. The effect is mediated by the respective neuropeptide receptors, can be mimicked by phorbol ester and blocked by inhibitors of protein kinases. Together with data from site-directed mutagenesis our results suggest that inflammatory mediators sensitize nociceptors through phosphorylation of P2X(3) and P2X(2/3) ion channels or associated proteins.
Subject(s)
Adenosine Triphosphate/pharmacology , Bradykinin/pharmacology , Receptors, Purinergic P2/physiology , Substance P/pharmacology , Amino Acid Sequence , Amino Acid Substitution , Animals , Chlorides/metabolism , Female , In Vitro Techniques , Kinetics , Membrane Potentials/drug effects , Membrane Potentials/physiology , Mutagenesis, Site-Directed , Neurons/physiology , Neuropeptides/physiology , Nociceptors/physiology , Oocytes/physiology , Protein Conformation , Protein Subunits , Receptors, Purinergic P2/chemistry , Receptors, Purinergic P2/drug effects , Receptors, Purinergic P2X2 , Receptors, Purinergic P2X3 , Recombinant Fusion Proteins/chemistry , Recombinant Fusion Proteins/drug effects , Recombinant Fusion Proteins/metabolism , Tetradecanoylphorbol Acetate/pharmacology , Xenopus laevisABSTRACT
P2X receptors are ion channels gated by extracellular ATP. We report here cloning of a P2X(2) receptor splice variant (P2X(2-2)) carrying a 207 bp deletion in the intracellular C-terminus and the analysis of the corresponding genomic structure of the P2X(2) gene. P2X(2-2) is as highly expressed as the original P2X(2) sequence in various tissues. ATP-activated currents mediated by heterologous expressed P2X(2) or P2X(2-2) receptors showed significant differences in desensitization time constants and steady-state currents in the continuous presence of ATP. These results imply functional differences between cells differentially expressing these P2X(2) isoforms.
