Stimulus–secretion coupling in neurohypophysial nerve endings: A role for intravesicular sodium?
AUTOR(ES)
Thirion, Sylve
FONTE
The National Academy of Sciences
RESUMO
It is generally accepted that Ca is essentially involved in regulated secretion, but the role of this cation, as well as others such as Na, is not well understood. An illustrative example occurs in neurohypophysial secretion, where an experimentally induced increase in the cytosolic concentration of Na+ can induce continuous neuropeptide release. In contrast, an increase in cytosolic Ca2+ will have only a transient stimulatory effect. The secretion-promoting targets for Ca2+ are not known; they may be cytosolic, as is usually assumed, but they may also be intravesicular, especially in view of evidence that Ca-rich secretory vesicles are preferentially secreted. In the present work, we have investigated the movements of these cations into and out of secretory vesicles during stimulus–secretion coupling. Isolated rat neurohypophysial nerve endings were stimulated by potassium (55 mM) depolarization, and at 6 min (peak secretion) and 20 min after the onset of stimulation, the elemental content of individual secretory vesicles was measured by quantitative x-ray microanalysis. A depolarization-induced transient increase in intravesicular Na+ concentration was found to coincide with the onset of secretion. Moreover, only a predicted small fraction of peripheral vesicles—presumably the docked ones—were Na+-loaded. The low sulfur concentration of Na+-rich vesicles most likely resulted from vesicle swelling. The results suggest that high intravesicular Na+ concentrations in docked vesicles, occurring by Na+/Ca2+ exchange or by transient fusion pore opening, is a proximal event in exocytosis.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=15920Documentos Relacionados
- Modulation of stimulus-secretion coupling in single rat gonadotrophs.
- Reversible fatigue of stimulus-secretion coupling in the rat neurohypophysis.
- Stimulus-secretion coupling in chromaffin cells isolated from bovine adrenal medulla
- Stimulus-secretion coupling in rat mast cells: inactivation of extracellular calcium dependent secretion.
- Multiple signaling pathways control stimulus-secretion coupling in rat peritoneal mast cells.