Secretion in dissociated human pulmonary mast cells. Evidence for solubilization of granule contents before discharge

Gastrointestinal mast cells in health and disease. Part I

The mast cell granule provides three distinct sources of mediators: (1) preformed and rapidly released (histamine), (2) secondarily formed and generated by the interaction of primary mediators and nearby cells and tissues (leukotrienes), and (3) granule matrix-derived, which are preformed but remain associated with the granule proteoglycans after discharge (proteases) (Table). The granule matrix and its associated mediators may remain in the tissue for hours until removed through degradation, dissolution, or phagocytosis. The events initiated by the mediators depend on the tissues into which they are released. Mediator discharge clearly initiates the events associated with immediate hypersensitivity; however, late-phase reactions occur in response to granule-derived mediators as well. Several manifestations that may result from the introduction of mast cell-derived products within the gastrointestinal tract are shown in Fig. 5. These include increased vascular permeability and secretion of mucus, effects on cell surface receptors, chemotaxis of various cell types, and smooth muscle contraction. Thus the mast cell, because of its unique anatomic location and mediators, may serve both as an initiator of acute inflammation and a propagator of chronic changes as well.

The characteristics of inhibition of histamine release from human lung fragments by sodium cromoglycate, salbutamol and chlorpromazine

1 Three drugs have been tested for activity against antigen-induced histamine release from passively sensitized human lung fragments after increasing periods of pre-incubation before challenge.2 After 30 s pre-incubation, sodium cromoglycate inhibited histamine release in the concentration range 0.2-200 muM, producing a maximum inhibition of 33.0%. As the pretreatment period was extended, tolerance developed in a dose-related manner, resulting in a 48.3% and 82.8% loss of activity of the 200 muM dose after 60 min and 19 h pre-incubation, respectively. Tolerance was independent of extracellular calcium and was poorly reversible. Lung tissue desensitized to cromoglycate was cross-tolerant to the related drug, bufrolin, but not to salbutamol or chlorpromazine.3 In acute studies, salbutamol (0.03-3.0 muM) produced dose-related inhibition of histamine release, with a maximum inhibition of 72.2%. The effect was blocked stereoselectively by 1 muM propranolol, suggesting that it occurred through an interaction with lung beta-adrenoceptors. Increasing the pre-incubation time with salbutamol from 30 s to 19 h did not produce tolerance. Inhibition produced by incubation with salbutamol for 19 h was totally prevented when propranolol was added at the beginning of the pre-incubation period, indicating that it resulted from stimulation of beta-receptors and not from a non-specific or toxic effect. However, studies of reversibility of effect through washing or late addition of propranolol did indicate some change in the nature of salbutamol inhibition with time.4 Chlorpromazine was a weak inhibitor of immunological histamine release. A 100 muM concentration was ineffective after 30 s pre-incubation but its activity increased with time. Pre-incubation of lung fragments with this concentration for 1 h or longer, or with a 1 mM dose for a shorter period, provoked histamine release in the absence of antigen. Effects of chlorpromazine were not reversed by washing.5 The different characteristics shown by sodium cromoglycate, salbutamol and chlorpromazine indicate that these drugs inhibit histamine release by interfering with the secretory mechanisms in different ways.

Secretory cells of the oviduct of the pig-tailed monkey, Macaca nemestrina, during the menstrual cycle and after estrogen treatment

The secretory cells of the oviductal epithelium in the pig-tailed monkey, Macaca nemestrina, have been studied by light and electron microscopy. Changes during the menstrual cycle and after ovariectomy, with and without subsequent estrogen treatment, have been documented. During the early follicular phase the epithelium is recovering from deciliation and secretory cell atrophy that occur in the late luteal phase. A few fimbrial and a moderate number of ampullar and isthmic cells contain a few electron-dense, homogeneous secretory granules in their apical cytoplasm. During the late preovulatory and early post-ovulatory periods, secretory cell structure varies considerably. Fimbrial cells typically display apical protrusions that contain no or a few small, mainly homogeneous, secretory granules. The cytoplasm is crowded with elements of the Golgi complex, with granular endoplasmic reticulum profiles often intimately associated with mitochondria, and with variable numbers of polysomes and glycogen granules. In ampullar and isthmic cells secretory granules are more abundant than in fimbrial cells, and electron-lucent vacuoles appear. The granules are of two types: 1) those having an electron-dense, homogeneous matrix, and 2) those possessing lamellar structures within moderately dense matrices. The lamellae of the second type course in parallel arrays separated by a distance of approximately 15.5 nm and exhibit a periodicity of approximately 11.3 nm. Possible transitional stages between the lamellar granules and the vacuoles containing lamellar fragments are observed. Secretion occurs by exocytosis. During the late luteal phase no fimbrial cells have secretory granules. In the ampulla many of the cells have poor development of the organelles involved in secretory activity and have few or no secretory granules. In others, a moderate number of secretory granules are present; in one animal, exocytosis is observed. In the untreated ovariectomized animal no secretory granules occur, and the organelle content is much less than in the cycling and the estrogen-treated monkeys. In ovariectomized, estradiol-treated monkeys, some areas of all three oviductal segments are well stimulated whereas others display little or no secretory activity.

Quantification of ultrastructural variations in enriched blood basophils: correlation of morphological changes and antigen-induced histamine release

Highly purified preparations of human basophils have been studied ultrastructurally to delineate quantifiably those alterations associated with immunologically-induced histamine release. Of six characteristic variations of basophil morphology, totally degranulated cells, those with some exteriorized granules and those with some extracellular vesicles were almost exclusively associated with antigen challenge. Of these, total degranulation without extracellular granules or vesicles was most frequent. A correlation was found between percentage histamine released and percentage totally degranulated cells present in the samples incubated with antigen. In addition, increased plasma membrane folding and irregularity were more prevalent in stimulated samples than in controls and their mean frequency was related quantifiably to the percentage of histamine released in each group. Cells with empty vesicles or electronlucent intracellular granules or both occurred to the same extent in experimental and control aliquots. The possible of histamine release is discussed.

The number and affinity of IgE receptors on dispersed human lung mast cells

Mast cells obtained by fragmentation of human lung tissue retained the capacity to bind IgE and to respond to immunological challenge. Direct binding studies with radiolabelled IgE enabled quantification of binding parameters of the reaction between IgE and its receptor on human mast cells. The average equilibrium constant was estimated as 1.0 x 10(8) M -1 and the average number of IgE receptors per mast cell as 1.3 x 10(5).

Secretory protein decondensation as a distinct, Ca2+-mediated event during the final steps of exocytosis in Paramecium cells

The contents of secretory vesicles ("trichocysts") were isolated in the condensed state from Paramecium cells. It is well known that the majority portion of trichocysts perform a rapid decondensation process during exocytosis, which is visible in the light microscope. We have analyzed this condensed leads to decondensed transition in vitro and determined some relevant parameters. In the condensed state, free phosphate (and possibly magnesium) ions screen local surplus charges. This is supported by x-ray spectra recorded from individual trichocysts (prepared by physical methods) in a scanning transmission electron microscope. Calcium, as well as other ions that eliminate phosphate by precipitation, produces decondensation in vitro. Under in vivo conditions, Ca2+ enters the vesicle lumen from the outside medium, once an exocytic opening has been formed. Consequently, within the intact cell, membrane fusion and protein decondensation take place with optimal timing. Ca2+ might then trigger decondensation in the same way by precipitating phosphate ions (as it does in vitro) and, indeed, such precipitates (again yielding Ca and P signals in x-ray spectra) can be recognized in situ under trigger conditions. As decondensation is a unidirectional, rapid process in Paramecium cells, it would contribute to drive the discharge of the secretory contents to the outside. Further implications on the energetics of exocytosis are discussed.

Mechanisms of exocytosis in phagocytic inflammatory cells. Parke-Davis Award Lecture

Images

Role of adenylate cyclase in immunologic release of mediators from rat mast cells: agonist and antagonist effects of purine- and ribose-modified adenosine analogs

The initial monophasic rise in cyclic AMP beginning 5-15 sec after bridging of rat mast cell IgE-Fc receptors precedes the secretion of granule constituents, thereby implying a causal relationship. Direct evidence for a relationship between IgE-dependent transmembrane activation of adenylate cyclase and granule secretion was provided by the capacity of purine-modified (R site active) and ribose-modified (P site active) adenosine analogs, respectively, to augment and suppress mediator release while simultaneously increasing and decreasing the activity of adenylate cyclase. R site stimulation alone does not cause granule secretion but augments the rate and magnitude of IgE-Fc receptor-induced secretion, reflecting the coupled relationship of such receptors. Inhibition of adenylate cyclase at the P site attenuates the rise in cellular cyclic AMP and suppresses IgE-dependent mediator release in a parallel and superimposable dose-response fashion. Further, the relationship between the attenuation in the rise in cyclic AMP and the diminution in immunologic mediator release is linear with the regression line passing through the origin, indicating a direct relationship between the IgE-dependent activation of adenylate cyclase and preformed mediator release. Although not the only events in coupled mast cell activation--secretion, there is a sequential relationship among perturbation of IgE-Fc receptors, transmembrane activation of adenylate cyclase, elevation of cytoplasmic levels of cyclic AMP, activation of cyclic AMP-dependent protein kinase, and secretion of mast cell granules.