Vesicle recycling at the mouse neuromuscular junction

PERISSINOTTI PP; GIUGOVAZ TROPPER B; UCHITEL OD

Cordoba

Congreso; Congreso anual de la Sociedad Argentina de Investigación en Neurociencias; 2006

Recycling of used synaptic vesicles is important to maintain the efficacy of synaptic transmission. Two principal recycling strategies have been described. In one, a single vesicular pool supplies the exocytose machinery with pre-formed vesicles, and is replenished via clathrin-mediated endocytosis. In the other, subsets of vesicles recycle at or near individual active zones. Despite the initial studies of vesicle recycling carried out at the mammalian neuromuscular junction (Ribchester et al, 1994, Reid et al 1999), a detailed study of the differentiation and modulation of the vesicle pools has not been performed. We studied mouse levator auris longus nerve terminals staining and destaining using imaging FM 2-10 dye. We also used conventional electro physiological techniques to measure endplate potentials. There are at least two different pools of recycling vesicles: one preferentially loaded during the first 250 action potentials delivered at 50 Hz, with a capacity of less than 15 % of the maximum loading capacity and high probability of release, and another one, a low release probability pool, loaded during and after stimulation. Dye release was completely blocked by omega-Agatoxin, at any rate of stimulation. At high frequency synaptic transmission, Ca2+ influx through L-type channels directs the newly formed vesicles to a high release probability pool. In absence of L-type Ca2+ influx, vesicle refilling during stimulation is diminished, suggesting the suppression of a fast recycling mechanism. As a consequence of diminished endocytosis during stimulation, there is an increase amount of membrane endocytosed after tetanus.