title: Guinea-pig sympathetic neurons express varying proportions of two distinct P2X receptors.
abstract: 1. Characterization of P2X receptors on neurons of guinea-pig superior cervical ganglion (SCG) has been carried out using a whole-cell voltage-clamp technique. 2. Application of ATP and alpha,beta-methylene ATP (alphabeta-MeATP) produced fast activating inward currents, which desensitized slowly. The maximum response to alphabeta-MeATP was 36 +/- 23 % (range 0.1-100 %) of that evoked by ATP in the same cell. 3. Co-application of alphabeta-MeATP (300 microM) with ATP (300 microM) produced a response that was 97 +/- 1 % of that given by ATP alone. Following desensitization with alphabeta-MeATP, the decrease in response to ATP was equal to the absolute reduction in response to alphabeta-MeATP in the same cell. 4. The concentration-response curve for alphabeta-MeATP had an EC50 of 42 microM and a Hill coefficient of 1.17. For cells where the ratio of alphabeta-MeATP/ATP currents at 100 microM was < 0.1, the ATP concentration-response curve had an EC50 of 56 microM and a Hill coefficient of 1.95. However, in cells where the ratio was > 0.7, the curve had an EC50 of 60 microM and a Hill coefficient of 0.97. 5. The response to 100 microM alphabeta-MeATP was inhibited by 2' (or 3')-O-trinitrophenyl-ATP (TNP-ATP) with an IC50 of 70 nM. However, on cells where the ratio of alphabeta-MeATP/ATP currents was < 0.1, ATP was inhibited by TNP-ATP with an IC50 of 522 nM. 6. Immunohistochemical staining with antibodies raised against rat P2X2 and P2X3 epitopes suggested that both subunits were expressed by guinea-pig SCG neurons. 7. We conclude that varying proportions of two distinct P2X receptors coexist on the cell bodies of individual guinea-pig SCG neurons, which may correspond to homomeric P2X2 and heteromeric P2X2/3 receptors.
authors.affiliation: Autonomic Neuroscience Institute, Department of Anatomy and Developmental Biology, Royal Free and University College Medical School, Rowland Hill Street, London NW3 2PF, UK. y.zhong@ucl.ac.uk
authors.forename: Y
authors.initials: Y
authors.lastname: Zhong
authors.forename: P M
authors.initials: PM
authors.lastname: Dunn
authors.forename: G
authors.initials: G
authors.lastname: Burnstock
mesh_terms: D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000320:Adrenergic Fibers / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D000906:Antibodies / Q000494:pharmacology; D000918:Antibody Specificity; D001667:Binding, Competitive / Q000187:drug effects; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D006168:Guinea Pigs; D007150:Immunohistochemistry; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D058910:Purinergic P2 Receptor Agonists; D058919:Purinergic P2 Receptor Antagonists; D018048:Receptors, Purinergic P2 / Q000096:biosynthesis*; D058476:Receptors, Purinergic P2X2; D058477:Receptors, Purinergic P2X3; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors; D017783:Superior Cervical Ganglion / Q000166:cytology
chemical_list: D000906:Antibodies; C546403:P2rx2 protein, rat; C546410:P2rx3 protein, rat; D058910:Purinergic P2 Receptor Agonists; D058919:Purinergic P2 Receptor Antagonists; D018048:Receptors, Purinergic P2; D058476:Receptors, Purinergic P2X2; D058477:Receptors, Purinergic P2X3; D011994:Recombinant Proteins; C045674:2',3'-O-(2,4,6-trinitro-cyclohexadienylidine)adenosine 5'-triphosphate; D000255:Adenosine Triphosphate; C002630:alpha,beta-methyleneadenosine 5'-triphosphate