P2X7 receptors in the enteric nervous system of guinea‐pig small intestine

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Abstract
The P2X7 purinergic receptor subtype has been cloned and emphasized as a prototypic P2Z receptor involved in neurotransmission in the central nervous system and ATP‐mediated lysis of macrophages in the immune system. Less is known about the neurobiology of P2X7 receptors in the enteric nervous system (ENS). We studied the distribution of the receptor with indirect immunofluorescence and used selective agonists and antagonists to analyze pharmacologic aspects of its electrophysiologic behavior as determined with intracellular “sharp” microelectrodes and patch‐clamp recording methods in neurons identified morphologically by biocytin injection in the ENS. Application of ATP or 2`‐ (or‐3`‐) O‐(4‐benzoylbenzoyl) adenosine 5`‐triphosphate (BzBzATP) activated an inward current in myenteric neurons. Brilliant blue G, a selective P2X7 antagonist, suppressed the responses to both agonists. Potency of the antagonist was greatest (smaller IC50) for the current evoked by BzBzATP. The P2X7 antagonists 1‐[N,O‐bis (1,5‐isoquinolinesulfonyl)‐N‐methyl‐l‐tyrosyl]‐4‐piperazine (KN‐62) and oxidized ATP also suppressed the BzBzATP‐activated current. Micropressure application of BzBzATP evoked rapidly activating depolarizing responses in intracellular studies with “sharp” microelectrodes. Oxidized‐ATP suppressed these responses in both myenteric and submucosal neurons. Rapidly activating depolarizing responses evoked by application of nicotinic, serotonergic 5‐HT3, or γ‐aminobutyric acid A (GABAA) receptor agonists were unaffected by brilliant blue G. Immunoreactivity for the P2X7 receptor was widely distributed surrounding ganglion cell bodies and associated with nerve fibers in both myenteric and submucous plexuses. P2X7 immunoreactivity was colocalized with synapsin and synaptophysin and surrounded ganglion cells that contained either calbindin, calretinin, neuropeptide Y, substance P, or nitric oxide synthase. The mucosa, submucosal blood vessels, and the circular muscle coat also showed P2X7 receptor immunoreactivity. J. Comp. Neurol. 440:299–310, 2001.