Endocytosis of secretory granules in mouse pancreatic beta-cells evoked by transient elevation of cytosolic calcium.
AUTOR(ES)
Eliasson, L
RESUMO
1. To investigate the mechanisms regulating the reuptake of secretory granule membranes following regulated exocytosis, we have monitored changes in cell capacitance in single pancreatic beta-cells. 2. Membrane retrieval (endocytosis) occurred both in a continuous manner and in abrupt steps, corresponding to the simultaneous retrieval of 50-100 granules. The large endocytotic steps were associated with a conductance change of about 1 nS which we attribute to the formation of a fission pore with a pore radius of approximately 1 nm. 3. In some cells, we observed large amplitude capacitance fluctuations, suggesting that aggregates of granules are connected to the plasma membrane by a single pore and are subsequently retrieved as a single unit. 4. Endocytosis was evoked by elevation of cytosolic [Ca2+]i, but once initiated, a sustained increase in [Ca2+]i was not required for endocytosis to continue. 5. The [Ca2+]i dependence of exo- and endocytosis was studied by photorelease of Ca2+ from the 'caged' precursor Ca(2+)-nitrophenyl-EGTA (Ca(2+)-NP-EGTA). Both exo- and endocytosis were initiated at between 0.5 and 2 microM Cai(2+). The rate of endocytosis saturated above 2 microM Cai(2+), whereas exocytosis continued to increase up to 4 microM Cai(2+). The maximum rate of endocytosis was < 25% of that of exocytosis. 6. Unlike exocytosis, endocytosis proceeded equally well in the presence or absence of Mg-ATP. 7. Our data indicate that in the pancreatic beta-cell, exocytosis and endocytosis are regulated by different mechanisms.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1159023Documentos Relacionados
- Calcium and delayed potassium currents in mouse pancreatic beta-cells under voltage-clamp conditions.
- The electrical activity of mouse pancreatic beta-cells recorded in vivo shows glucose-dependent oscillations.
- Cyclic adenosine monophosphate differently affects the response of mouse pancreatic beta-cells to various amino acids.
- Block of ATP-regulated and Ca2(+)-activated K+ channels in mouse pancreatic beta-cells by external tetraethylammonium and quinine.
- Ca(2+)- and GTP-dependent exocytosis in mouse pancreatic beta-cells involves both common and distinct steps.