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 Follow Intense Exocytosis in Chromaffin Cells
Autor/es:
PEREZ BAY AE; MARENGO FD
Lugar:
Melbourne, Australia
Reunión:
Congreso; 7th IBRO World Congress of Neuroscience; 2007
Institución organizadora:
International Brain Research Organization
Resumen:
Rapid Recovery of Releasable Vesicles and Formation of Non-Releasable Endosomes Follow Intense Exocytosis in Chromaffin Cells                                                              Andrés E. Pérez Bay and Fernando D. Marengo. Laboratorio de Fisiología y Biología Molecular. Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires. IFIBYNE – CONICET. Argentina. Neurons and neuroendocrine cells retrieve excess of plasmamembrane and refill depleted vesicle pools after exocytosis. It is expected that the selection of a particular endocytosis/recycling pathway will impact in the recycling time of releasable vesicles. In this work we tried to discriminate the endocytosis-recycling responses produced by a variety of stimuli respect to their ability to rapidly generate releasable vesicles. Using FM 1-43 in chromaffin cells, we evaluated in the same experiment the Ca2+-triggered exocytosis, the resulting endocytosis and the internalized membrane fraction cycled to releasable vesicles. Moderate exocytosis induced by cholinergic agonists was followed by total recovery of releasable vesicles. If a stronger stimulus (50mM K+, 2mM Ca2+) provoking intense exocytosis was applied, endocytosis still retrieved all the fused membrane, but only a fraction was releasable by a second stimulus. Using ADVASEP-7 or bromophenol-blue after exocytosis to quickly eliminate fluorescence coming from non-internalized FM1-43, we determined that this fraction became releasable in < 2 min, indicating that vesicular cycling is completed in this short timeframe. As the remaining non-releasable fraction was mainly distributed as big fluorescent spots (~0.7 mm), it was selectively labeled by 40kD dextrans, and its formation was inhibited by a PI 3-kinase inhibitor, we believe that it might be the result of a bulk retrieval process. Thus, chromaffin cells can rapidly recover important fractions of their vesicle population, and this pathway prevails when cholinergic agonists were used as secretagogues. Masive exocytosis also triggers an additional mechanism, which is unable to quickly produce secretory vesicles but seems to be crucial for membrane surface homeostasis.