Degranulation of individual mast cells in response to Ca2+ and guanine nucleotides: an all-or-none event.
Open Access
- 1 November 1993
- journal article
- Published by Rockefeller University Press in The Journal of cell biology
- Vol. 123 (3), 585-593
- https://doi.org/10.1083/jcb.123.3.585
Abstract
Widespread experience indicates that application of suboptimal concentrations of stimulating ligands (secretagogues) to secretory cells elicits submaximal extents of secretion. Similarly, for permeabilized secretory cells, the extent of secretion is related to the concentration of applied intracellular effectors. We investigated the relationship between the extent of secretion from mast cells (assessed as the release of hexosaminidase) and the degranulation (exocytosis) responses of individual cells. For permeabilized mast cells stimulated by the effector combination Ca2+ plus GTP-gamma-S and for intact cells stimulated by the Ca2+ ionophore ionomycin, we found that exocytosis has the characteristics of an all-or-none process at the level of the individual cells. With a suboptimal stimulus, the population comprised only totally degranulated cells and fully replete cells. In contrast, a suboptimal concentration of compound 48/80 applied to intact cells induced a partial degree of degranulation. This was determined by observing the morphological changes accompanying degranulation by light and electron microscopy and also as a reduction in the intensity of light scattered at 90 degrees, indicative of a change in the cell-refractive index. These results may be explained by the existence of a threshold sensitivity to the combined effectors that is set at the level of individual cells and not at the granule level. We used flow cytometry to establish the relationship between the extent of degranulation in individual rat peritoneal mast cells and the extent of secretion in the population (measured as the percentage release of total hexosaminidase). For comparison, secretion was also elicited by applying the Ca2+ ionophore ionomycin or compound 48/80 to intact cells. For permeabilized cells and also for intact cells stimulated with the ionophore, levels of stimulation that generate partial secretion gave rise to bimodal frequency distributions of 90 degrees light scatter. In contrast, a partial stimulus to secretion by compound 48/80 resulted in a single population of partially degranulated cells, the degree of degranulation varying across the cell population. The difference between the all-or-none responses of the permeabilized or ionophore-treated cells and the graded responses of cells activated by compound 48/80 is likely to stem from differences in the effective calcium stimulus. Whereas cell stimulated with receptor-directed agonists can undergo transient and localized Ca2+ changes, a homogeneous and persistent stimulus is sensed at every potential exocytotic site in the permeabilized cells.Keywords
This publication has 32 references indexed in Scilit:
- Exocytotic fusion is activated by Rab3a peptidesNature, 1992
- Nucleotides and divalent cations as effectors and modulators of exocytosis in permeabilized rat mast cellsPhilosophical Transactions Of The Royal Society B-Biological Sciences, 1992
- Techniques and concepts in exocytosis: focus on mast cellsBiochimica et Biophysica Acta (BBA) - Reviews on Biomembranes, 1991
- Time–resolved capacitance measurements: monitoring exocytosis in single cellsQuarterly Reviews of Biophysics, 1991
- Protien phosphorylation and the dependence on Ca2+ and GTP-γ-S for exocytosis from permeabilised mast cellsCellular Signalling, 1989
- Rat mast cells permeabilised with streptolysin O secrete histamine in response to Ca2+ at concentrations buffered in the micromolar rangeBiochimica et Biophysica Acta (BBA) - Molecular Cell Research, 1987
- Calcium-dependence of catecholamine release from bovine adrenal medullary cells after exposure to intense electric fieldsThe Journal of Membrane Biology, 1982
- Ionomycin stimulates mast cell histamine secretion by forming a lipid-soluble calcium complexNature, 1979
- Plasma membrane folds on the mast cell surface and their relationship to secretory activity.The Journal of cell biology, 1977
- A Family of Long-Acting DepressorsJournal of the American Chemical Society, 1949