Effect of purinergic receptor antagonists on high K+- and electrically-evoked ACh secretion at mammalian neuromuscular junctions (MNJ)

JAVIER GONZÁLEZ SANABRIA; MAXIMILIANO HURTADO PASO; JUAN GUARRACINO; ADRIANA LOSAVIO

Mar del Plata

Congreso; XXX Congreso Anual Sociedad Argentina de Investigación en Neurociencias; 2015

Sociedad Argentina de Investigación en Neurociencias

At mammalian NMJ, ATP and its metabolite adenosine decrease ACh release by activation of presynaptic P2Y12-13 and A1 receptors (R), respectively. Our aim was to analyze the effect of endogenous purines on K+- and electrically-evoked ACh secretion. In phrenic-diaphragm preparations (CF1 mice), we studied the action of selective antagonists of P2Y12-13R (2 µM AR-C69931MX) and A1R (0.1 µM DPCPX) upon MEPP frequency (10, 15, 20 mM K+) and on EPP amplitude when the nerve was stimulated at 0.5, 5 or 50 Hz (train or bursts). AR-C69931MX induced an increase in MEPP frequency at 10, 15 and 20 mM K+ whereas DPCPX did not modify asynchronic secretion at 10 mM K+, but provoked a significant increase at 15 and 20 mM K+. On the other hand, AR-C69931MX and DPCPX did not change the amplitude of the first EPP in any of the studied frequencies. At 50 Hz (750 pulses or 5 bursts of 150 pulses), the antagonists diminished the declination of EPP amplitude that normally occurs during repetitive stimulation. There was not a significant difference at 0.5 and 5 Hz. We suggest that depolarization of motor nerve endings by high K+ concentrations or 50 Hz-stimulation generates endogenous ATP/ADP and adenosine able to modulate ACh secretion. These findings raise the possibility that selective P2Y12-13R and A1R antagonists can be used therapeutically to assist in the treatment of neuromuscular disorders such as myasthenia gravis, in which the prejunctional depression can produce life-threatening effects.