P2X7 receptors contribute to the currents induced by ATP in guinea pig intestinal myenteric neurons
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The whole-cell configuration, several pharmacological tools, and single-cell RT-PCR were used to investigate the contribution of P2X7 subunits to the ATP-induced currents (I ATP) in guinea pig myenteric neurons. I ATP was recorded in the great majority of tested neurons. ATP concentration-response curve (0.01-10 mM) showed two phases, the first mediated by high-sensitive P2X receptors (hsP2X receptors), observed between 0.01-0.3 mM and the second mediated by low-sensitive P2X receptors (lsP2X receptors). The calculated EC 50 values of these phases were 38 and 1759 μM, respectively. 2′-3′-O-(4-benzoylbenzoyl)-ATP (BzATP) concentration-response curve was monophasic (0.01-1 mM), and less potent (EC 50 142 μM) than ATP to activate hsP2X receptors. A strong inward rectification was noticed when hsP2X receptors were activated with ATP (0.1 mM) and for BzATP-induced currents (0.1 mM; I BzATP) but a significant lower rectification was noticed when lsP2X receptors were activated (5 mM). Brilliant blue G (BBG) at a concentration of 0.3 μM (known to inhibit only P2X7 receptors) reduced I ATP when lsP2X receptors contributed to it but neither affect hsP2X receptors nor I BzATP. However, hsP2X receptors and I BzATP were both inhibited by concentrations ≥ 1 μM of this antagonist. BzATP inhibited hsP2X receptors and therefore, it behaves as partial agonist on these receptors. Using the single-cell RT-PCR technique P2X7 mRNA was detectable in 7 out of 13 myenteric neurons exhibiting P2X2 mRNA. Altogether, our results show that low-sensitive P2X receptors are likely P2X7, whereas, the high-sensitive P2X channels are probably constituted, at least in part, by P2X2 subunits. © 2011 Elsevier B.V. All rights reserved.
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(Guinea pig); Enteric neurons; Myenteric plexus; P2X receptors; P2X2 receptors; Patch-Clamp; RT-PCR; Small intestine 2',3' o (4 benzoylbenzoyl) adenosine triphosphate; adenosine triphosphate; messenger RNA; purinergic P2X7 receptor; receptor blocking agent; unclassified drug; animal cell; animal experiment; article; concentration (parameters); concentration response; controlled study; gene; intestine muscle; median effective concentration; nerve cell; nonhuman; nucleotide sequence; P2X2 gene; P2X7 gene; priority journal; protein function; reverse transcription polymerase chain reaction; RNA sequence; Adenosine Triphosphate; Animals; Dose-Response Relationship, Drug; Electrophysiological Processes; Female; Guinea Pigs; Intestines; Male; Myenteric Plexus; Neurons; Receptors, Purinergic P2X7; RNA, Messenger
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