Neonatal Capsaicin-treated rats have reduced extracellular
purine levels in the Myenteric Plexus
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1
Instituto de Ciencias Biomedicas Abel Salazar - Universidade do Porto (ICBAS-UP), Laboratorio de Farmacologia e Neurobiologia, Unidade Multidisciplinar de Investigacao Biomedica (UMIB), Portugal
Extracellular adenine nucleotides and adenosine are versatile signalling molecules implicated in an array of cell-specific responses [1]. Neurochemistry studies provided evidence that purines, ATP and ADO, modulate acetylcholine release from electrically-stimulated myenteric neurons [2,3]. In the rat myenteric plexus, endogenous adenosine (ADO) may arise from the catabolism of released ATP through the ectonucleotidase pathway together with the release of the nucleoside per se through the equilibrative transport system [4]. Using the luciferin-luciferase bioluminescence assay, we now evaluated whether ATP release paralleled extracellular adenosine (ADO) accumulation upon stimulating (5 Hz, 3000 pulses) the longitudinal muscle - myenteric plexus (LM-MP) of the rat ileum [4]. We focused our attention to purines originated from tachykinergic nerve fibres, which can be selectively eliminated (<95%) after neonatal capsaicin administration (50 mg/Kg, SC).
Electrical stimulation of the LM-MP of the rat ileum increased extracellular ATP levels by a similar proportion (306±68%, n=8) to that observed for the outflow of adenine nucleosides (ADO+INO, 261±40%, n=9). Similarly to that occurring with ADO+INO accumulation [4], blockade of nerve action potentials with tetrodotoxin (1 μM) reduced ATP release to 61±51% (n=4), but there were no significant changes (P<0.05) upon blocking the muscular component with atropine (1 mM) plus nifedipine (5 μM). In vitro application of capsaicin (10 μM) led to a significant (P<0.05) increase in ATP (462±83%, n=4) and ADO+INO (417±114%, n=2) accumulation. In contrast, ATP and ADO+INO levels decreased in preparations collected from neonatal capsaicin-treated rats to 90±22% (n=5) and to 136±22% (n=9), respectively. The amount of adenosine detected in LM-MP of neonatal capsaicin-treated rats may be slightly overestimated due to a parallel reduction in the activity of ecto- adenosine deaminase, the key enzyme for adenosine inactivation which is also secreted from myenteric neurons [4]. Data suggest that capsaicin-sensitive tachykinergic neurons may be an important source of purines in the rat myenteric plexus.
This work was supported by FCT (FEDER funding, PTDC/CVT/74462/2006 and UMIB-215/94).
References
1. Yegutkin (2008) Biochim Biophys Acta., 1783, 673-694
2. Duarte-Araujo et al (2009) Br J Pharmacol
3. Duarte-Araujo et al (2004) Br J Pharmcol., 141, 925-934
4. Correia-de-Sá et al (2006) Auton Neurosci., 127, 211-224
Conference:
11th Meeting of the Portuguese Society for Neuroscience, Braga, Portugal, 4 Jun - 6 Jun, 2009.
Presentation Type:
Poster Presentation
Topic:
Neuronal Communication
Citation:
Marques
P,
Duarte-Araujo
M,
Silva
I,
Vieira
C,
Almeida
M,
Magalhaes-Cardoso
T and
Correia- De-Sa
P
(2009). Neonatal Capsaicin-treated rats have reduced extracellular
purine levels in the Myenteric Plexus.
Front. Neurosci.
Conference Abstract:
11th Meeting of the Portuguese Society for Neuroscience.
doi: 10.3389/conf.neuro.01.2009.11.146
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Received:
12 Aug 2009;
Published Online:
12 Aug 2009.
*
Correspondence:
Patricia Marques, Instituto de Ciencias Biomedicas Abel Salazar - Universidade do Porto (ICBAS-UP), Laboratorio de Farmacologia e Neurobiologia, Unidade Multidisciplinar de Investigacao Biomedica (UMIB), Porto, Portugal, tixa_marques@hotmail.com