Abstract
Purinergic signaling was first recognized in the guinea pig (Cavia porcellus) taenia coli, where relaxation of smooth muscle by nerve-released ATP may involve the activation of P2Y1 and P2Y11 receptors, and where transcripts for both genes have been found. A partial sequence for P2Y11 protein was identified; the full-length P2Y1 sequence has already been described. P2Y1 and P2Y11 proteins were localized by immunohistochemistry in smooth muscle cells. P2X2 and P2X3 proteins were also localized in motoneurons of the myenteric plexus. αβ-Methylene-ATP (αβmeATP) and dibenzoyl-ATP (BzATP) evoked fast relaxations in the taenia, and they were inhibited by the P2Y1 receptor antagonist 2′-deoxy-N6-methyladenosine 3′,5′-bisphosphate (MRS2179). However, αβmeATP and BzATP may stimulate neuronal P2X receptors to release ATP, which then acts on P2Y1 receptors. In accordance, fast relaxations evoked by αβmeATP and BzATP were inhibited by the P2X3 and P2X2/3 receptor antagonist 5-({[3-phenoxybenzyl][(1S)-1,2,3,4-tetrahydro-1-naphthalenyl] amino} carbonyl)-1,2,4-benzene-tricarboxylic acid (A317491). When P2Y1, P2X3, and P2X2/3 receptors were blocked and adenosine was removed enzymatically, αβmeATP and BzATP evoked slow relaxations that were inhibited by Reactive Red. Fast and slow relaxations involve small and large conductance calcium-activated potassium channels; the latter are dependent on intracellular cyclic AMP levels, which altered the duration and amplitude of relaxations. αβmeATP and BzATP were confirmed as agonists, and Reactive Red as an antagonist, of human P2Y11 receptors. In summary, Gq-coupled P2Y1 receptors are involved mainly in fast relaxations, whereas Gqand Gs-coupled P2Y11 receptors are involved in both fast and slow relaxations. These P2Y receptor subtypes, plus neuronal P2X receptors, may explain the phenomenon of parasympathetic inhibition first described by Langley (1898).
Footnotes
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A.T.-N. is funded by British Heart Foundation Grants FD/99049 and PG2001052.
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Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
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doi:10.1124/jpet.107.131169.
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ABBREVIATIONS: SMC, smooth muscle cell; IJP, inhibitory junction potential; SKCa, small conductance calcium-activated potassium channel; BKCa, large conductance calcium-activated potassium channel; NO, nitric oxide; VIP, vasoactive intestinal peptide; PACAP, pituitary adenylyl cyclase-activating peptide; BzATP, dibenzoyl-ATP; αβmeATP, α,β-methylene-ATP; PCR, polymerase chain reaction; FLIPR, fluorometric imaging plate reader; C/R, concentration-response; DAPI, 4′,6-diamidino-2-phenylindole; MRS2179, 2′-deoxy-N6-methyladenosine 3′,5′-bisphosphate; A317491, 5-({[3-phenoxybenzyl][(1S)-1,2,3,4-tetrahydro-1-naphthalenyl] amino} carbonyl)-1,2,4-benzene-tricarboxylic acid; ADA, adenosine deaminase; ISO, isoprenaline; Ro-20-1724, 4-(3-butoxy-4-methoxyphenyl)methyl-2-imidazolidone; PPADS, pyridoxal phosphate-6-azophenyl-2′,4′-disulfonic acid; ARC67085, 2-propylthio-βγCl2meATP; ir, immunoreactivity.
- Received September 3, 2007.
- Accepted November 28, 2007.
- The American Society for Pharmacology and Experimental Therapeutics
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