Multivesicular exocytosis in rat pancreatic beta cells.
Diabetologia
; 55(4): 1001-12, 2012 Apr.
Article
en En
| MEDLINE
| ID: mdl-22189485
ABSTRACT
AIMS/HYPOTHESIS:
To establish the occurrence, modulation and functional significance of compound exocytosis in insulin-secreting beta cells.METHODS:
Exocytosis was monitored in rat beta cells by electrophysiological, biochemical and optical methods. The functional assays were complemented by three-dimensional reconstruction of confocal imaging, transmission and block face scanning electron microscopy to obtain ultrastructural evidence of compound exocytosis.RESULTS:
Compound exocytosis contributed marginally (<5% of events) to exocytosis elicited by glucose/membrane depolarisation alone. However, in beta cells stimulated by a combination of glucose and the muscarinic agonist carbachol, 15-20% of the release events were due to multivesicular exocytosis, but the frequency of exocytosis was not affected. The optical measurements suggest that carbachol should stimulate insulin secretion by â¼40%, similar to the observed enhancement of glucose-induced insulin secretion. The effects of carbachol were mimicked by elevating [Ca(2+)](i) from 0.2 to 2 µmol/l Ca(2+). Two-photon sulforhodamine imaging revealed exocytotic events about fivefold larger than single vesicles and that these structures, once formed, could persist for tens of seconds. Cells exposed to carbachol for 30 s contained long (1-2 µm) serpentine-like membrane structures adjacent to the plasma membrane. Three-dimensional electron microscopy confirmed the existence of fused multigranular aggregates within the beta cell, the frequency of which increased about fourfold in response to stimulation with carbachol. CONCLUSIONS/INTERPRETATION:
Although contributing marginally to glucose-induced insulin secretion, compound exocytosis becomes quantitatively significant under conditions associated with global elevation of cytoplasmic calcium. These findings suggest that compound exocytosis is a major contributor to the augmentation of glucose-induced insulin secretion by muscarinic receptor activation.
Texto completo:
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Bases de datos:
MEDLINE
Asunto principal:
Islotes Pancreáticos
/
Vesículas Secretoras
/
Células Secretoras de Insulina
/
Exocitosis
/
Insulina
Límite:
Animals
Idioma:
En
Revista:
Diabetologia
Año:
2012
Tipo del documento:
Article
País de afiliación:
Reino Unido