P2X(7) receptors in the enteric nervous system of guinea-pig small intestine

The P2X(7) purinergic receptor subtype has been cloned and emphasized as a prototypic P2Z receptor involved in neurotransmission in the central nervou s system and ATP-mediated lysis of macrophages in the immune system. Less i s known about the neurobiology of P2X(7) receptors in the enteric nervous s ystem (ENS). We studied the distribution of the receptor with indirect immu nofluorescence and used selective agonists and antagonists to analyze pharm acologic aspects of its electrophysiologic behavior as determined with intr acellular "sharp" microelectrodes and patch-clamp recording methods in neur ons identified morphologically by biocytin injection in the ENS. Applicatio n of ATP or 2'- (or-3'-) O-(4-benzoylbenzoyl) adenosine 5'-triphosphate (Bz BzATP) activated an inward current in myenteric neurons. Brilliant blue G, a selective P2X(7) antagonist, suppressed the responses to both agonists. P otency of the antagonist was greatest (smaller IC50) for the current evoked by BzBzATP. The P2X(7) antagonists 1-[N,O-bis (1,5-isoquinolinesulfonyl)-N -methyl-l-tyrosyl]-4-piperazine (KN-62) and oxidized ATP also suppressed th e BzBzATP-activated current. Micropressure application of BzBzATP evoked ra pidly activating depolarizing responses in intracellular studies with "shar p" microelectrodes. Oxidized-ATP suppressed these responses in both myenter ic and submucosal neurons. Rapidly activating depolarizing responses evoked by application of nicotinic, serotonergic 5-HT3, or gamma -aminobutyric ac id A (GABA(A)) receptor agonists were unaffected by brilliant blue G. Immun oreactivity for the P2X(7) receptor was widely distributed surrounding gang lion cell bodies and associated with nerve fibers in both myenteric and sub mucous plexuses. P2X(7) 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 mu cosa, submucosal blood vessels, and the circular muscle coat also showed P2 X(7) receptor immunoreactivity. J. Comp. Neurol. 440:299-310, 2001. (C) 200 1 Wiley-Liss, Inc.