IFIBYNE   05513
INSTITUTO DE FISIOLOGIA, BIOLOGIA MOLECULAR Y NEUROCIENCIAS
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Rapid recovery of releasable vesicles and formation of non releasable endosomes after compensatory endocytosis and excess retrieval
Autor/es:
ANDRÉS PÉREZ BAY; A. VERONICA BELINGHERI; YANINA D. ALVAREZ; FERNANDO D. MARENGO
Lugar:
Mérida. México.
Reunión:
Congreso; 15th Internacional Symposium of Chromaffin Cell Biology; 2009
Institución organizadora:
Internacional Symposium of Chromaffin Cell Biology
Resumen:
Rapid recovery of releasable vesicles and formation of non releasable endosomes AFTER COMPENSATORY ENDOCYTOSIS AND EXCESS RETRIEVAL. Andrés E. Perez Bay1, Ana Verónica Belingheri1, Yanina Álvarez1 and Fernando D. Marengo1,2. Laboratorio de Fisiología y Biología Molecular, Facultad de Ciencias Exactas y Naturales, IFIByNE (UBA-CONICET)1. Cátedra de Biofísica, Facultad de Odontología2. Universidad de Buenos Aires, Buenos Aires, Argentina. Endocytosis and vesicular cycling are critical for maintaining the membrane surface and vesicle pools in neuroendocrine cells and neurons. Cells can use different pathways/mechanisms, whose selection will impact on vesicle recycling time and secretion performance. We used FM1-43 to evaluate, during the same experiment, the exocytosis induced by a variety of stimuli, the endocytosis, and the recovery of releasable vesicles on mouse chromaffin cells. For all the stimulus conditions tested (high K+, cholinergic agonists, reversion of Na/Ca exchanger, various external Ca2+ concentrations) we observed that endocytosis finally equaled exocytosis. However, under certain conditions (stimuli≤30s), a transitory excess retrieval phenomenon (endocytosis > exocytosis) was observed consistently, which was highly dependent on the Ca2+ signal. In all the conditions studied in this work an important fraction of the retrieved membrane was rapidly cycled into releasable vesicles (in ≤2 s after the end of stimulus). However, this cycling pathway was limited to ~20% of total plasmamembrane, since larger exocytosis had to be compensated by internalization of a fraction of membrane that was not cycled to releasable vesicles, at least in our experimental time periods. This fraction was concentrated in ~700 nm diameter endosomes selectively labeled by 40-70 kD dextrans, showing characteristics of bulk endocytosis. Excess retrieval, which is associated to a rapid endocytosis pathway, made a major contribution to the generation of this non releasable fraction. We concluded that chromaffin cells can rapidly recycle significant fractions of their total vesicle population, and that this pathway prevails in conditions of low to middle exocytic challenge. When exocytosis exceeded ~20% of plasma membrane, an additional mechanism was activated, which was unable to produce secretory vesicles in our experimental timeframe but seemed crucial to maintain the membrane surface homeostasis under extreme conditions. This additional mechanism seems to progress rapidly after strong stimulus application, surpassing exocytosis transiently and provoking excess retrieval.