PERSONAL DE APOYO
VEGGETTI Mariela Iris
artículos
Título:
Effect of purines on calcium-independent acetylcholine release at the mouse neuromuscular junction
Autor/es:
MARIELA I. VEGGETTI, S MUCHNIK, ADRIANA LOSAVIO
Revista:
NEUROSCIENCE
Editorial:
PERGAMON-ELSEVIER SCIENCE LTD
Referencias:
Lugar: Amsterdam; Año: 2008 vol. 154 p. 1326 - 1336
ISSN:
0306-4522
Resumen:
At the mouse neuromuscular junction,
activation of adenosine A1 and P2Y receptors inhibits acetylcholine
release by an effect on voltage dependent calcium channels related to spontaneous
and evoked secretion. However, an effect of purines upon the neurotransmitter-releasing
machinery downstream of Ca2+ influx cannot
be ruled out. An excellent tool to study neurotransmitter exocytosis in a Ca2+-independent step is the hypertonic response.
Intracellular recordings were performed on diaphragm fibers of CF1 mice to
determine the action of the specific adenosine A1 receptor agonist
2-chloro-N6-cyclopentyl-adenosine (CCPA) and the P2Y12-13 agonist
2-methylthio-
adenosine 5?-diphosphate (2-MeSADP) on the
hypertonic response. Both purines significantly decreased such response (peak
and area under the curve), and their effect was prevented by specific
antagonists of A1 and P2Y12-13 receptors, 8-cyclopentyl- 1,3-dipropylxanthine
(DPCPX) and N-[2-(methylthioethyl)]-2-[3,3,3-trifluoropropyl]thio-5=-adenylic acid, monoanhydride with
dichloromethylenebiphosphonic acid, tetrasodium salt (AR-C69931MX), respectively.
Moreover, incubation of preparations only with the antagonists induced a higher
response compared with controls, suggesting that endogenous ATP/ADP and
adenosine are able to modulate the hypertonic
response by activating their specific
receptors. To search for the intracellular pathways involved in this effect, we
studied the action of CCPA and 2-MeSADP in hypertonicity in the presence
of inhibitors of several pathways. We found that
the effect of CPPA was prevented by the calmodulin antagonist N-(6-aminohexil)-5-chloro-1-naphthalenesulfonamide
hydrochloride (W-7) while that of 2-MeSADP was occluded by the protein kinase C
antagonist chelerythrine and W-7. On the other hand, the inhibitors of protein
kinase A (N-(2[pbromocinnamylamino]-ethyl)-5-isoquinolinesulfonamide,
H-89) and phosphoinositide-3 kinase (PI3K) (2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one
hydrochloride, LY-294002) did not modify the modulatory action in hypertonicity
of both purines. Our results provide evidence that activation of A1 and P2Y12-13
receptors by CCPA and 2-MeSADP inhibits ACh release from mammalian motor nerve
terminals through an effect on a Ca2_-independent step in the cascade of the
exocytotic process. Since presynaptic calcium channels are intimately
associated with components of the synaptic vesicle docking and fusion
processes, further experiments could clarify if the actions of purines on calcium
channels and on secretory machinery are related.