Adenosine modulates the fast release vesicle pool at mouse neuromuscular junction

PERISSINOTTI PP; UCHITEL OD

Cordoba

Congreso; IRCN First Joint Meeting of the Argentine Society for Neurosciences (SAN) and the Argentine Workshop in Neurosciences (TAN); 2009

At mouse neuromuscular junction (NMJ) there are two different pools of recycling vesicles: a high probability release pool (i.e. a fast destaining vesicle pool), which is preferentially loaded during the first 5 seconds at 50 Hz, and a low probability release pool (i.e. a slow destaining vesicle pool) which is loaded during prolonged stimulation and keeps on refilling after end of stimulation (Perissinotti et al., 2008. Eur J Neurosci. 27(6):1333-44). It has been reported that presynaptic receptors play a role in adjusting the pattern of neuromuscular transmission. Modulation of Ca2+ currents at mammalian NMJ occurs through hydrolysis of ATP to adenosine, followed by the activation of adenosine inhibitory (A1 and A3) and excitatory (A2A and A2B) receptors. On the other hand, it is known that noradrenaline increases transmitter release at the mammalian NMJ and may affect neuromuscular transmission through stimulation of presynaptic alpha-1 adrenoceptors. However, whether adenosine and noradrenaline may regulate vesicle recycling is a question which has not been addressed until now. We used fluorescence microscopy of FM2-10-labeled synaptic vesicles and electrophysiological recordings to examine whether adenosine and noradrenaline have a role on vesicle recycling. We found that the quantal content significantly decreased by 60 % in presence of adenosine (300 uM) either at low (5 Hz) or high (50 Hz) frequency stimulation, suggesting an inhibitory effect. We studied the effect of adenosine, DPCPX (A1 antagonist) and phenylephrine (alpha-1 adrenoceptor agonist) on the amount of FM2-10 loaded during 5 seconds at 50 Hz. No differences were observed. However, dye unloading during a second round of stimulation was faster when the dye was loaded in presence of DPCPX (0.1 uM) but not in presence of phenylephrine (10 uM). This result showed that vesicles formed in the presence of DPCPX have a higher probability of release, suggesting that adenosine receptors are involved in fast endocytosis modulation.