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Am J Physiol Regul Integr Comp Physiol (February 1, 2007). doi:10.1152/ajpregu.00785.2006
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Submitted on November 10, 2006
Accepted on January 30, 2007

Developmental Changes of Purinergic Control of Intestinal Motor Activity During Metamorphosis in the African Clawed Frog, Xenopus laevis.

Monika Sundqvist1*

1 Zoophysiology, University of Göteborg, Göteborg, Sweden

* To whom correspondence should be addressed. E-mail: monika.sundqvist{at}zool.gu.se.

Little is known about the purinergic regulation of intestinal motor activity in amphibians. Purinergic control of intestinal motility is subject to changes during development in mammals. The aim of this study was to investigate purinergic control of intestinal smooth muscle in the amphibian Xenopus laevis and explore possible changes in this system during the developmental phase of metamorphosis. Effects of purinergic compounds on mean force and contraction frequency in intestinal circular muscle strips from prometamorphic, metamorphic and juvenile animals were investigated. Prior to metamorphosis, low concentrations of ATP reduced motor activity while the effects were reversed at higher concentrations. ATP-induced relaxation was not inhibited by the P2-receptor antagonist pyridoxalphosphate-6-azophenyl-2’,4’-disulfonic acid (PPADS) but blocked by the ecto-nucleotidase inhibitor 6-N,N-diethyl-D-{beta},{gamma}-dibromomethyleneATP (ARL67256), indicating that an ATP-derived metabolite mediated the relaxation response at this stage. Adenosine induced relaxation prior to, during and after metamorphosis, which was blocked by the A1-receptor antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX). The stable ATP-analogue adenosine 5’-[{gamma}-thio]-triphosphate (ATP{gamma}S) and 2-methylthioATP (2-MeSATP) elicited contractions in the circular muscle strips in prometamorphic tadpoles. However, in juvenile froglets, 2-MeSATP caused relaxation, as did ATP{gamma}S at low concentrations. The P2Y11/P2X1-receptor antagonist NF157 antagonised the ATP{gamma}S-induced relaxation. The P2X-preferring agonist {alpha}-{beta}-methyleneadenosine 5’-triphosphate ({alpha}-{beta}-MeATP) evoked PPADS-sensitive increases in mean force at all stages investigated. This study demonstrates the existence of an adenosine A1-like receptor mediating relaxation and a P2X-like receptor mediating contraction in the Xenopus laevis gut prior to, during and after metamorphosis. Furthermore, the development of a P2Y11-like receptor-mediated relaxation during metamorphosis is shown.







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