P2X purinoceptors in cultured myenteric neurons of guinea-pig small intestine.
1. Fast excitatory postsynaptic currents (fEPSCs) and responses to exogenously applied purinoceptor agonists were studied in primary cultures of myenteric neurons from guinea-pig small intestine. Whole-cell and outside-out configurations of the patch clamp technique were used. Hexamethonium (100 microM) partly inhibited fEPSCs in 28% of neurons. Hexamethonium-resistant fEPSCs were inhibited by 97 +/- 2% by the P2X receptor antagonist, pyridoxal-phosphate-6-azophenyl-2',4'-disulphonic acid (PPADS, 10 microM). 2. ATP caused two types of inward currents. In 92% of neurons (n = 123), ATP caused a slowly desensitizing current that declined with a double exponential time course (tau 1 = 7.1 +/- 2.0 s; tau 2 = 57 +/- 7.4 s, n = 4). The rank order potency for purinoceptor agonists in these neurons was ATP > 2-methylthio-ATP (2-MeSATP) > > alpha, beta-methylene ATP (alpha, beta-me ATP) > beta, gamma-meATP > ADP. The EC50 values for ATP and 2-MeSATP were 40 and 65 microM, respectively. alpha, beta-MeATP acted as a partial agonist at these receptors. In 8% of neurons (n = 11), ATP-induced currents desensitized rapidly with a double exponential time course (tau 1 = 0.13 +/- 0.015 s; tau 2 = 2.2 +/- 1.3 s, n = 4); alpha, beta-meATP caused similar responses in these cells. Both types of ATP-induced current were associated with an increased conductance and an inwardly rectifying I-V relationship (Erev = 10 mV). Halving [Na+]o shifted the reversal potential of ATP currents by -22 +/- 6 mV. 3. ATP activated single channel currents in outside-out patches. The single channel I-V relationship was linear between -120 and 60 mV (Erev approximately 0 mV). Single channel conductance between -100 and -60 mV was 25 +/- 2 pS. Single channel open probability was voltage dependent and decreased from 0.05 +/- 0.01 at -100 mV to 0.007 +/- 0.002 at +40 mV. 4. These data show that P2X purinoceptors mediate some fEPSCs in cultured myenteric neurons. Myenteric neurons express the fast-desensitizing alpha, beta-me ATP-sensitive subtype of P2X receptor that has the properties of cloned P2X1 receptors and is similar to native receptors in smooth muscle cells. Myenteric neurons also express a P2X receptor that desensitized slowly and was alpha, beta-meATP-insensitive. This receptor has the properties of cloned P2X2 or P2X5 receptors and is similar to native receptors found in PC-12 cells and superior cervical ganglion neurons. The known distribution of P2X2 and P2X5 receptors suggests that myenteric neurons are likely to express predominantly P2X2 receptors.
Zhou
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Department of Pharmacology and Toxicology, Michigan State University, East Lansing, USA.
Galligan
J J
JJ
D000244:Adenosine Diphosphate / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives* / Q000494:pharmacology*; D000818:Animals; D000831:Animals, Newborn; D002478:Cells, Cultured; D005071:Evoked Potentials / Q000187:drug effects; D006168:Guinea Pigs; D018738:Hexamethonium / Q000494:pharmacology; D007421:Intestine, Small / Q000294:innervation*; D007700:Kinetics; D009130:Muscle, Smooth / Q000294:innervation; D009197:Myenteric Plexus / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques; D018048:Receptors, Purinergic P2 / Q000187:drug effects / Q000502:physiology*; D013329:Structure-Activity Relationship; D009435:Synaptic Transmission / Q000187:drug effects; D013997:Time Factors
D018048:Receptors, Purinergic P2; D018738:Hexamethonium; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate