Current concepts on the secretory function of mast cells

Lipopolysaccharide-dependent interaction between PU.1 and c-Jun determines production of lipocalin-type prostaglandin D synthase and prostaglandin D2 in macrophages

Previously, we reported that expression of lipocalin-prostaglandin D synthase (L-PGDS) is inducible in macrophages and protects from Pseudomonas pneumonia. Here, we investigated the mechanism by which L-PGDS gene expression is induced in macrophages. A promoter analysis of the murine L-PGDS promoter located a binding site of PU.1, a transcription factor essential for macrophage development and inflammatory gene expression. A chromatin immunoprecipitation assay showed that PU.1 bound to the cognate site in the endogenous L-PGDS promoter in response to LPS. Overexpression of PU.1, but not of PU.1(S148A), a mutant inert to casein kinase II (CKII) or NF-kappaB-inducing kinase (NIK), induced L-PGDS in RAW 264.7 cells. Conversely, siRNA silencing of PU.1 expression blunted productions of L-PGDS and prostaglandin D2 (PGD(2)). LPS treatment induced formation of the complex of PU.1 and cJun on the PU.1 site, but inactivation of cJun by treatment with JNK or p38 kinase inhibitor abolished the complex, and suppressed PU.1 transcriptional activity for L-PGDS gene expression. Together, these results show that PU.1, activated by CKII or NIK, cooperates with MAPK-activated cJun to maximally induce L-PGDS expression in macrophages following LPS treatment, and suggest that PU.1 participates in innate immunity through the production of L-PGDS and PGD(2).

Increased levels of prostaglandin D(2) suggest macrophage activation in patients with primary pulmonary hypertension

STUDY OBJECTIVE

TXA(2) (thromboxane A(2)) is a lipid mediator believed to be produced primarily by platelets in normal subjects, although macrophages are capable of synthesis. There is increased production of TXA(2) in patients with primary pulmonary hypertension (PPH), which may reflect augmented production by macrophages. The objective of this study was to determine if macrophages are activated in PPH and whether they contribute to the increased production of TXA(2).

STUDY TYPE

Case control.

SETTING

University hospital.

METHODS

We measured the urinary metabolites of three mediators that predominantly derive from different cell types in vivo: (1) TX-M (platelets and macrophages), a TXA(2) metabolite; (2) prostaglandin D(2) (PGD(2)) metabolite (PGD-M); and (3) N-methylhistamine (mast cells), a histamine metabolite, in 12 patients with PPH and 11 normal subjects.

RESULTS

The mean (+/- SEM) excretion of both TX-M and PGD-M at baseline was increased in PPH patients, compared to normal subjects (460 +/- 50 pg/mg creatinine vs 236 +/- 16 pg/mg creatinine [p = 0.0006], and 1,390 +/- 221 pg/mg creatinine vs 637 +/- 65 pg/mg creatinine [p = 0.005], respectively). N-methylhistamine excretion was not increased compared to normal subjects. There was a poor correlation between excretion of TX-M and PGD-M (r = 0.36) and between excretion of PGD-M and methylhistamine (r = 0.09) in individual patients.

CONCLUSION

In patients with PPH, increased levels of PGD-M, without increased synthesis of N-methylhistamine, suggest that macrophages are activated. The lack of correlation between urinary metabolite levels of TXA(2) and PGD(2) implies that macrophages do not contribute substantially to elevated TXA(2) production in patients with PPH. They may, however, have a role in the pathogenesis and/or maintenance of PPH, which warrants further investigation.

Histamine lipolytic activity and semicarbazide-sensitive amine oxidase (SSAO) of rat white adipose tissue (WAT)

Histamine has previously been described as a possible substrate for the semicarbazide-sensitive amine oxidase activity (SSAO) of rat white adipose tissue (WAT). We report here on a histamine function in this tissue which concerns the activity of this deaminating system distinct from the classical diamine oxidase. Our results show that: (1) histamine plays a role in controlling rat adipose tissue lipolysis with the contribution of H1 and H2 receptors that participate in histamine lipolysis in an opposite way. Both H1 and H2 roles can be differentiated using selective agonists (2- and 4-methyl histamine) and antagonists (pyrilamine and cimetidine); (2) histamine might also control rat lipolysis induced by noradrenergic agonists; (3) the SSAO present in rat WAT controls histamine levels at the receptor sites as shown by the modification of histamine lipolytic potency obtained when inhibitors of this enzyme are used.

In vivo microdialysis measurement of histamine in rat blood effects of compound 48/80 and histamine receptor antagonists

An in vivo microdialysis method combined with a highly sensitive HPLC method which was developed for the analysis of the mediators in the CNS has been applied to assay histamine concentrations in the blood. The technique was used to study the effects of compound 48/80 and histamine receptor antagonists on histamine release in the blood of rats. The mean basal level of histamine in the blood measured by in vivo microdialysis was 177.8 +/- 11.1 pmol/mL. This level was not affected significantly by intraperitoneal (i.p.) injection of saline, and remained at the constant level for at least 8 hr after injection of saline. After i.p. injection of histamine (0.5 mg/kg), histamine was quickly detected in the blood of the jugular vein. Moreover, because the recovered histamine in the dialysate is directly proportional to the free fraction in the blood, the in vivo microdialysis method of blood is a reliable method of examining histamine release into the blood. In our experiments, the histamine level in dialysates from rat jugular vein was markedly increased by compound 48/80 (2.0 mg/kg, i.p.), demonstrating the histamine release into the blood from mast cells. However, there was no increase in histamine concentration after an i.p. injection of histamine receptor antagonists, such as pyrilamine (2.0 mg/kg), d-chlorpheniramine (2.0 mg/kg), cimetidine (10 mg/kg), or thioperamide (10 mg/kg). Thus, the present results suggested that these histamine receptor antagonists might not have an influence on histamine release into the blood.

Release of histamine in rat hypothalamus and corpus striatum in vivo

Histamine has remained a putative neurotransmitter for many years, partially because some of the criteria necessary to define it as a central nervous system neurotransmitter have not been established. The demonstration of in vitro release and the quantification of turnover as an indirect measure of release have been complicated by the histological evidence for multiple histamine pools in the central nervous system. In brain, there are multiple cell types which probably contain histamine. These cells include mast cells, neurolipomastocytoid cells, microvascular endothelial cells, and a histaminergic neuronal system which has been visualized using immunocytochemical methods. Using in situ brain microdialysis and a sensitive and specific radioenzymatic assay for histamine, we have identified histamine in the extracellular space of the rat hypothalamus and corpus striatum in vivo. Following neuronal selective stimuli, significant increases in extracellular histamine levels only were observed in the posterior hypothalamus, where dense histaminergic neuronal terminals have been described. However, after manipulations targeted towards histamine-containing mast cells, such increases were seen in both the posterior hypothalamus and corpus striatum. In summary, this study demonstrates that endogenous histamine can be released from the posterior hypothalamus by stimuli targeted towards histamine neurons and that histamine may also be released by non-neuronal mast cell elements.

Mast cells in ulcerative colitis. Quantitative and ultrastructural studies

The changes in the number and ultrastructure of mast cells were studied in 37 colonoscopical biopsies from patients with ulcerative colitis. Changes in the active stage of the disease and during remission were compared. Cell counts were performed on semithin sections stained with Giemsa after osmium tetroxide fixation. This method overcome the uncertain staining found after formalin fixation. Accumulation of mast cells accompanied by intense degranulation was found to be significant in the active stage of the disease. Two forms of degranulation were observed: discharge of the individual granules and protrusion and detachment of the cytoplasmic processes containing granules. The latter was a sign of rapid degranulation, as described earlier in animal experiments. Mast cells were closely associated with capillary blood vessels, Schwann cells, neural fibres, myofibroblasts and collagenous fibres, and were also present between epithelial cells. It is assumed that close topographic contact may also imply a functional correlation.

Regulation of the production of a prolactin-like protein (MRP/PLF) in 3T3 cells and in the mouse placenta

Mitogen-regulated protein (MRP), a heterogeneously glycosylated mouse protein of Mr 34,000, is in the same protein family as prolactin, growth hormone, and placental lactogen. We show here that the level of translatable MRP mRNA is increased in response to fibroblast growth factor. Also, the amount of MRP secreted by 3T3 cells is modulated by the rate of degradation of newly synthesized MRP in the lysosomes. This is indicated by several results. First, agents that inhibit protein degradation by lysosomal proteases selectively increased by 2- to 6-fold the incorporation of [35S]methionine into MRP. These agents are ammonium chloride, the carboxylic ionophores, monensin and nigericin, and two thiol protease inhibitors, leupeptin and antipain. MRP that has already been secreted is not degraded by 3T3 cells. We examined the developmental appearance of MRP using immunofluorescence microscopy and found MRP localized in the mouse placenta between days 9 and 13 of development. The amount of MRP in the placenta drops suddenly after day 13. Whereas the appearance of MRP in the placenta follows the reported appearance of its mRNA, MRP disappears from the placenta more rapidly than its mRNA. On the basis of the results of our studies with cells in culture we propose that the production of MRP in the placenta is regulated similarly to prolactin. Thus we propose that the initial increase in MRP production in the placenta is due to pretranslational regulation by growth factors, and the later rapid decline is due to posttranslational regulation through degradation in the lysosomes.

Modulation of the spontaneous histamine release by adrenergic and cholinergic drugs

Experiments have been reported on the possible modulation of the spontaneous histamine release by adrenergic and cholinergic drugs. Adrenergic drugs increase the spontaneous histamine release in vivo, and in neoplastic mast cells, in vitro. The mechanism of histamine release appears to be dependent upon the activation of alpha-adrenoceptors. Cholinergic drugs activate the release of histamine in many secretory processes in vivo; in vitro, acetylcholine is one of the most powerful histamine releasers in isolated purified rat mast cells. The release of histamine evoked by acetylcholine in rat mast cells is a calcium-requiring, temperature-dependent exocytosis. The physiological relationship of the sympathetic, parasympathetic and histamine-containing cells are discussed.

Requirement for metalloendoprotease in exocytosis: evidence in mast cells and adrenal chromaffin cells

Exocytosis is initiated by the receptor-mediated influx of calcium that results in fusion of the secretory vesicle with the plasma membrane. We examined the possibility that calcium-dependent exocytosis in mast cells and adrenal chromaffin cells requires metalloendoprotease activity. Metalloendoprotease inhibitors and dipeptide substrates block exocytosis in these cells with the same specificity and dose dependency as that with which they interact with metalloendoproteases. Metalloendoprotease activity is identified in these cells with fluorogenic synthetic substrates, which also blocked exocytosis. Metalloendoprotease activity is highest in the plasma membrane of chromaffin cells. The metalloendoprotease appears to be required in exocytosis at a step dependent on or after calcium entry, since exocytosis initiated by direct calcium introduction in both mast cells and chromaffin cells is blocked by metalloendoprotease inhibitors.

Mast cells in rat thalamus: nuclear localization, sex difference and left-right asymmetry

Mast cells were positively identified in rat brain by a combination of staining and histochemical procedures. These cells stained positively with toluidine blue and Astrablau at low pH, indicating the presence of a proteoglycan similar to that found in peripheral mast cells. Brain mast cells also fluoresced after o-phthalaldehyde exposure, indicating that they contain histamine. Mast cells varied greatly in number among brains, but their distribution was almost exclusively thalamic; within thalamus, the ventral complex, medial dorsal, lateral, and paraventricular nuclei contained the most mast cells. Mast cell numbers were greater in brains of females than of males, and greater in left than in right hemispheres. These findings suggest that mast cells have a specialized function in thalamus and/or that the vascular environment of the thalamus is particularly conducive to mast cell accumulation.

Inhibition of surfactant release from isolated type II cells by compound 4880

Release of [3H]phosphatidylcholine from pulmonary Type II epithelial cells was stimulated by terbutaline, forskolin and cytochalasin D. Compound 48/80 inhibited both basal and agonist-stimulated release of [3H]PC. The IC50 for inhibition by compound 48/80 was 1-2 micrograms/ml, and was similar for inhibition of both basal and stimulated release of [3H]phosphatidylcholine. Inhibitory effects of 48/80 were noted following a 1 h exposure to compound 48/80 and persisted up to 3 h. The inhibitory effect of compound 48/80 was entirely reversed by removing compound 48/80 from the external milieu. Compound 48/80 had no effect on cytosolic cyclic AMP levels or lactate dehydrogenase release. Inhibition of surfactant release produced by compound 48/80 was unaffected by changes in extracellular calcium concentrations. Compound 48/80 is a non-toxic inhibitor of phosphatidylcholine release from Type II epithelial cells.

Histamine content and histidine decarboxylase activity in the spleen of the magnesium-deficient rat: comparison with the skin and peritoneal mast cells

In young rats, some effects of magnesium (Mg) depletion in the diet on histamine content and histidine decarboxylase (HDC) activity in spleen were studied in comparison with those in the skin and peritoneal mast cells. In the case of the young rats fed a Mg-deficient diet (0.001% Mg), the splenic histamine contents increased to levels about 1.3, 2.8 and 23 times as high as those in the rats fed a control diet (0.07% Mg) on the 4th, 6th and 8th day, respectively; histamine contents in the peritoneal mast cells also increased to about 1.2 and 1.8 times the control levels on the 6th and 8th day, respectively; no change was observed in histamine contents in the skin during 8 days of Mg depletion. HDC activities in the spleen of Mg-deficient rats on the 4th, 6th and 8th day increased to levels about 5.5, 15.5 and 35 times as high as the respective control values; the activities in the skin increased to about 37, 7 and 10 times the control values on the 4th, 6th and 8th day, respectively; while in the peritoneal mast cells, the activities increased to about 1.2 and 2.2 times the control values on the 6th and 8th day, respectively. On the 8th day of the Mg deficiency, some studies were made on the effects of histamine releasers on histamine contents in the spleen and peritoneal mast cells. Compound 48/80 (0.5 microgram/ml) or polymyxin B (5 micrograms/ml) induced a release of histamine from the peritoneal mast cells, but not from the spleen cells isolated from the Mg-deficient rat in vitro.(ABSTRACT TRUNCATED AT 250 WORDS)

Stimulus-secretion coupling in rat mast cells: inactivation of extracellular calcium dependent secretion

1. Stimulation by compound 48/80 of mast cells deprived of Ca failed to release histamine. Secretion of histamine was elicited from such cells by the subsequent introduction of Ca. 2. Histamine secretion declined as the interval between stimulation by compound 48/80 and the introduction of Ca increased. This decline is called inactivation. 3. The addition of the ionophore, A23187, with Ca restored maximum histamine secretion overcoming inactivation. 4. Increasing the concentration of Ca introduced after stimulation, from 2 to 8 mM, or to 20 mM reduced the amount of histamine released. This reduction was proportional to the interval between stimulation and the introduction of Ca. The addition of A23187 with the higher concentrations of Ca fully restored histamine secretion. 5. Stimulation of mast cells in Ca-free media by the secretagogues polymyxin B or bradykinin, and the subsequent introduction of Ca, resulted in a similar inactivation or decline in histamine release. 6. Mast cells inactivated by compound 48/80 stimulation in Ca-free media showed no increase in histamine release when the secretagogues polymyxin B plus Ca or bradykinin plus Ca were added. However, when A23187 plus Ca was added, a full secretory response was obtained. 7. It is suggested that the process of inactivation involves time-dependent change in the Ca permeability of the mast cell membrane. The concentration of introduced Ca is suggested to influence the regulation of this permeability.

Neurotensin stimulates exocytotic histamine secretion from rat mast cells and elevates plasma histamine levels

1. Neurotensin stimulated histamine release and granule extrusion when applied to isolated rat peritoneal mast cells. 2. This secretory response was prevented by the removal of calcium or energy and was not accompanied by the release of lactic dehydrogenase. 3. The secretory response produced by neurotensin was prevented by prior treatment of mast cells with cromoglycate. 4. The intravenous injection of neurotensin into anaesthetized rats produced a rapid and significant increase in the level of blood histamine that was dependent upon the dose of neurotensin. 5. Treatment of rats with compound 48/80, 24 hr before neurotensin, abolished the elevation in blood histamine caused by neurotensin. The intravenous injection of cromoglycate 1-2 min before neurotensin greatly reduced the response to neurotensin. 6. The intradermal injection of neurotensin (0.03-30 p-mole) increased capillary permeability in rats pre-treated intravenously with Evans Blue. This response was abolished by the antihistamine, diphenhydramine. Increasing the dose of neurotensin to 300 p-mole partially overcame this inhibition by diphenhydramine. 7. Our results demonstrate that neurotensin can elicit an exocytotic secretory response from isolated rat peritoneal mast cells and elevate histamine levels in blood. It is suggested that some of neurotensin's physiological effects may be due to stimulation of mast cell secretion.

The effect of concentration on the binding of compound 48/80 to rat mast cells: a fluorescence microscopy study

A fluorescent analog of the chemical histamine liberator, compound 48/80, has been synthesized by the covalent attachment of rhodamine to the 48/80 polymer (R-48/80). The histamine liberating characteristics of this analog were similar to those of the parent compound. The binding characteristics of R-48/80 to rat peritoneal mast cells were then studied using fluorescence microscopy. At concentrations that caused minimal secretory stimulation (less than 1.0 microgram/ml), R-48/80 bound to the mast cell surface in a diffuse manner, with no indication of patching or capping. When the cells were incubated at higher concentrations, where non-cytotoxic histamine secretion was stimulated, the drug bound heavily to the exposed granules, but not to unexposed granules or other cell organelles. At cytotoxic concentrations, R-48/80 caused extensive cell clumping, with the drug bound to masses of cell debris and released granules. Therefore, although R-48/80 binds initially to the cell membrane, its primary binding site at concentrations that induce secretion becomes the mast cell granule. The properties of these granules should thus be considered when studying the binding of compound 48/80 or other cationic drugs to rat peritoneal mast cells.

Somatostatin-induced histamine secretion in mast cells. Characterization of the effect

Somatostatin, in concentrations up to 100 ng/ml, had no effect on mast cell secretion induced either by compound 48/80 or by the ionophore A23187. In higher concentration somatostatin induced mast cell secretion. Light and electron microscopic observations showed that the secretory response was identical with that induced by 48/80 and involved extrusion of secretory granules by exocytosis. As with 48/80, this response to somatostatin was inhibited by treating the mast cells with EDTA or EGTA or by exposing them briefly to A23187 in calcium-free media, all of which procedures seemingly deplete cellular calcium stores. Reintroduction of calcium (but not magnesium), restored secretory responsiveness. Somatostatin-induced secretion further resembled that induced by 48/80 or A23187 in its intensity, rapid time course, and dependence on albumin. Pretreatment of mast cells with dibutyryl cyclic AMP or 8-bromo cyclic AMP substantially reduced the secretory responses to both somatostatin and 48/80 but had little effect on the response to A23187. Somatostatin, like 48/80, lowered intracellular cyclic AMP levels in a time and dose-dependent fashion. Finally, as earlier found for 48/80, somatostatin attached to Sepharose columns retarded the passage of mast cells and elicited histamine release indicating an action at the cell surface. The stimulant action of somatostatin is thus very similar to that of the classic mast-cell secretagogue compound 48/80.

The effect of polymyxin B and some mast-cell constituents on mucosal mast cells in the duodenum of the rat

Mucosal mast cells in the rat duodenum show no morphological signs of exocytosis of granules and do not release histamine after treatment with polymyxin B in doses large enough to cause almost complete degranulation of connective-tissue mast cells of tongue, skin, and mesentery with concomitant release of approximately 60% of the tissue histamine. Administration of polymyxin B in gradually increasing doses over a period of 5 ds resulted in a statistically significant increase in mucosal mast cells and a comparable increase in duodenal histamine content, whereas the connective-tissue mast cells in the other tissues examined became fewer in number, the remaining cells showing profound morphological changes, and tissue histamine levels, were reduced to approximately 40% of the controls. A similar increase in mucosal mast cells has been observed after treatment with another mast-cell secretagogue, compound 48/80. This suggests that the increase in mucosal mast cells may be an indirect effect of these compounds, related to their activation of other mast cells and mediated by material(s) secreted by the connective-tissue mast cells. Possible mediators such as heparin, histamine, and 5-hydroxytryptamine injected for 5 ds in doses large enough to account for the amount released from the degranulated mast cells had no effect on the morphology or numbers of mast cells in any of the tissues examined.

Mast cell histamine, a local mitogen acting via H2-receptors in nearby tissue cells

The tissue mast cell is the major storage site of histamine in the body. The present study is concerned with the effect of one histamine H1- and one histamine H2-receptor antagonist on proliferation in the rat mesentery following drug-induced mast-cell secretion. The H2-receptor antagonist, but not the H1-receptor antagonist, significantly suppressed mast-cell-mediated proliferation in vivo and in organ-cultured mesentery. This finding indicates that mast-cell-histamine is a mitogen acting directly on histamine H2-receptors in surrounding tissue cells.

Phospholipid methylation and biological signal transmission

Many types of cells methylate phospholipids using two methyltransferase enzymes that are asymmetrically distributed in membranes. As the phospholipids are successively methylated, they are translocated from the inside to the outside of the membrane. When catecholamine neurotransmitters, lectins, immunoglobulins or chemotaxic peptides bind to the cell surface, they stimulate the methyltransferase enzymes and reduce membrane viscosity. The methylation of phospholipids is coupled to Ca2+ influx and the release of arachidonic acid, lysophosphatidylcholine, and prostaglandins. These closely associated biochemical changes facilitate the transmission of many signals through membranes, resulting in the generation of adenosine 3',5'-monophophate in many cell types, release of histamine in mast cells and basophils, mitogenesis in lymphocytes, and chemotaxis in neutrophils.

Gastrointestinal mast cells in health, and in coeliac disease and other conditions

Intestinal biopsies were performed in children suffering from coeliac and other diseases and were stained by the 'astra-blau' method for visualising granulated mast cells. The density of granulated mast cells (per microscopical field) in treated coeliac disease and in 3 control groups (patients suffering from milk allergy, failure to thrive, or protracted diarrhoea) was 15--18 cells per microscopical field, which contrasted with a mean of 6.8 cells in untreated coeliac disease. It is concluded that exposure to gluten in coeliac disease results in degranulation of mast cells, while exposure to milk in milk allergy has no such effect.

Rat ovarian mast cells: distribution and cyclic changes

Numerous tissue mast cells are present in the ovarian medulla and hilus and in the oviduct of rats. In the medulla, most of these mast cells are in the connective tissue of the stroma near blood and lymphatic vessels. During proestrus, many of the medullary mast cells totally degranulate and thus are not visible histochemically; they then regranulate during estrus. In contrast, the number of stainable mast cells in the ovarian hilus and oviduct does not change during the estrous cycle. Histofluorometric methods demonstrate that mast cells in the ovarian medulla and hilus, as well as the oviduct, contain histamine. In addition, the lining of small blood vessels in the ovarian medulla contains histamine. Thus, mast cell and blood vessel histamine secretion may play a role in ovarian function.

Evidence that histamine does not participate in carrageenan-induced pleurisy in rat

The injection of carrageenan into the rat pleural cavity provoked an intense inflammatory reaction with the formation of an exudate which contained mainly neutrophils but which was also rich in mast cells and histamine. There was, however, no evidence that histamine participated in the reaction. The mast cells remained intact, and no increase in extracellular histamine levels was observed. Prior treatment with bot H1 and H2 histimine receptor antagonists or depletion of the histamine stores by pretreatment with compound 48/80 did not alter the reaction. In contrast, the exudate formed in response to the intrapleural injection of small doses (0.05 mg/kg) of compound 48/80 was reduced by pretreatment with the antihistamine compounds and, unlike the exudate formed after carrageenan injection, was devoid of neutrophils. Since saline washes of the pleural cavity of untreated rats had histamine and mast cell contents similar to those of the exudates of the carrageenan-treated rats, the source of histamine appeared to be mast cells from the pleural cavity.

Antiallergic drug cromolyn may inhibit histamine secretion by regulating phosphorylation of a mast cell protein

Cromolyn inhibited histamine release from mast cells that was induced by a classic secretagogue and correspondingly increased incorporation of radioactive phosphate into a 78,000-dalton protein. These effects on histamine secretion and on protein phosphorylation were rapid in onset and both showed tachyphylaxis. Cromolyn may therefore act by altering the phosphorylation of a protein involved in the regulation of secretion.

Purification and partial characterization of an alpha-chymotrypsin-like protease of rat peritoneal mast cells

An alpha-chymotrypsin-like enzyme was isolated from mast cells of the rat peritoneal cavity by extraction with 0.8 M potassium phosphate, 2 per cent protamine sulfate followed by affinity chromatography on hen ovoinhibitor-agarose and adsorption on barium sulfate. This procedure yielded over 9 mg of protease from the peritoneal lavage fluid of 100 rats, equivalent to 44 per cent of the initial activity. The purified protein was homogeneous as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, analytical isoelectric focusing, and amino-terminal sequence analysis. The protease contains no covalently bound carbohydrate and has a molecular weight of approximately 26,000. The enzyme molecule is a single polypeptide chain with an amino-terminal sequence homologous to that of the B chain of bovine alpha-chymotrypsin. The kinetic parameters, Km and kcat, for the hydrolysis of N-benzoyl-L-tyrosine ethyl ester were determined at pH 8.0 and 25 degrees C as 1.1 X 10(-3) M and 84 sec-1, respectively. The value of the second-order rate constant for inactivation of mast cell protease by diisopropylphosphofluoridate was 300 times lower than for bovine alpha-chymotrypsin.

Histologic identification of mast cells in human dental pulp

Previous investigators who attempted to identify mast cells in the dental pulp have used demineralizing or tooth-splitting procedures to obtain their tissue samples. However, Eda and Langeland15 found that the fluorescence of mast cells is destroyed by acid demineralizing agents. On the other hand, tooth splitting may damage the pulp by crushing it with forceps, or cutting and heating it with burs, stones, or discs. In the present study, we used the extirpated pulps from teeth in which endodontic access openings were made by means of high-speed rotary instruments with water spray. Metachromatic staining methods failed to demonstrate mast cells in any of the non-inflamed pulp specimens. Two of the inflamed pulp specimens revealed numerous mast cells which appeared intact and well preserved with no evidence of degranulation. As to the distribution of the mast cells, there was no correlation with the number and types of other inflammatory cells observed. Although several cells present in the specimens examined were suggestive of mast cells, only those cells that revealed definitive metachromasia were included in this study.

Secretion in mast cells induced by calcium entrapped within phospholipid vesicles

Purified mast cells secreted histamine when fused to phospholipid vesicles containing calcium but not magnesium or potassium. Microscopic observation revealed highly localized exocytotic responses involving punctate extrusion of individual granules. Calcium delivered from the vesicles to the cytoplasm is apparently a sufficient stimulus to initiate exocytosis. The results support the calcium hypothesis of stimulus-secretion coupling.

The effect of beta-adrenergic blocking drugs and inhibitors of phosphodiestease on histamine release from isolated mast cells

Differences in the histamine liberation from isolated rat mast cells after beta-adrenergic blocking drugs were demonstrated. In equimolar concentrations histamine release was induced by Kö 1124, Kö 1500, Kö 1560, Kö 1561 and propranolol. Alprenolol, oxprenolol, propranolol, and trimepranol significantly decreased thehistamine release induced by compound 48-80. The release of granules from cells was inhibited quantitatively more than the release of histamine. This enabled us to surmise the selective effect of beta-adrenergic blocking drugs on cell membranes of mast cells. The possible mechanisms of release reaction are discussed.

Secretin-induced histamine release in duodenal-ulcer patients

Because a majority of duodenal-ulcer patients responded locally to intradermal secretin, skin samples from 7 patients with duodenal ulceration and 6 patients with goitre or cholelithiasis were incubated with "tris" buffer alone and with tris buffer containing 20 C.U./ml synthetic secretin or 100 microng/ml compound 48/80. Skin from duodenal-ulcer patients released significantly more histamine than did that of controls (p less 0-01). Histological examination of skin samples from these patients showed that the number of histamine-containing mast-cells averaged 5-7 per field and dropped to 1-2 per field after incubation with secretin. It is concluded that in a certain type of duodenal ulceration intradermal secretin releases histamine from mast-cells and thus induces a local anaphylactic reaction. This might prove suitable for preclinical ulcer diagnosis and/or for detection of patients at risk of acquiring that disease.

Changes in the coronary vascular system following prolonged exposure to stress

Hearts of stressed rats showed marked changes in the coronary vasculature. It was suggested that such morphological changes could be explained on the basis of an increased coronary vascular permeability. Endogenous inflammatory substances could induce swelling of the endothelial cells and cause separation of the neighbouring cells from one another, thus allowing the passage of lipid molecules through the endothelial lining. In order to gain supportive evidence for the above hypotheses an electron microscope study was undertaken. The presence of junctional gaps in the endothelial lining of the coronary vascular system was observed following prolonged stress, as well as platelet aggregation. The use of lipid staining of frozen sections indicated the presence of large lipid deposits in the arteriole walls, corresponding to vacuoles seen previously. It would appear therefore, that prolonged exposure to stress may result in pathological changes in the myocardium associated with changes in the vascular endothelial permeability, and platelet aggregation. Pathological changes induced in this way, however, should be inhibitd by high glucocorticoid levels and should not be manifested until adaptation of the steroid response to stress has occurred. Measurement of plasma glucocorticoid levels over the period of prolonged stress shows a good correlation between the adaptation of the steroid response and the onset of a progressive degeneration of the coronary vascular system.

The modulation of histamine release by alpha-adrenoceptors: evidences in murine neoplastic mast cells

Murine neoplastic mast cells which have been loaded with exogenous labelled histamine, released 14C-histamine when exposed to increasing concentrations of phenylephrine and noradrenaline. Adrenaline was only slightly effective, while isoprenaline and dibutyryl-cyclic-AMP were fully inactive. The release of histamine evoked by alpha-adrenergic agonists was antagonized by phentolamine, and left unchanged by practolol and cocaine. It is concluded that alpha-adrenoceptors may be valuable in evoking histamine release by murine neoplastic mast cells.

Isolated cortical granules: a model system for studying membrane fusion and calcium-mediated exocytosis

Cortical granules are secretory vesicles bound to the inner surface of the plasma membrane of sea urchin eggs. Intact granules can be isolated by shearing away the cytoplasm of eggs which have been bonded to a protamine-coated surface. When Ca2+ is added to preparations of isolated granules the granules fuse with each other and release their contents. It is believed that isolated cortical granules may be an excellent model system for the biochemical study of exocytosis.

Potassium-induced release of tritiated histamine from rat brain tissue slices

The release of exogenous histamine was studied by superfusing brain slices following incubation with the radiolabeled amine. Histamine was released in a calcium-dependent way by 40 mM potassium. This release was high in hypothalamus and striatum and low in hippocampus and cortex. Compound 48/80, a mast cell histamine releasing agent, also induced histamine release, but only from hypothalamic tissue slices. It is suggested that the potassium-induced release of accumulated exogenous histamine is mainly from glial cells.