Calcium-dependent protein phosphorylation during secretion by exocytosis in the mast cell

Potential Role of Moesin in Regulating Mast Cell Secretion

Mast cells have existed for millions of years in species that never suffer from allergic reactions. Hence, in addition to allergies, mast cells can play a critical role in homeostasis and inflammation via secretion of numerous vasoactive, pro-inflammatory and neuro-sensitizing mediators. Secretion may utilize different modes that involve the cytoskeleton, but our understanding of the molecular mechanisms regulating secretion is still not well understood. The Ezrin/Radixin/Moesin (ERM) family of proteins is involved in linking cell surface-initiated signaling to the actin cytoskeleton. However, how ERMs may regulate secretion from mast cells is still poorly understood. ERMs contain two functional domains connected through a long α-helix region, the N-terminal FERM (band 4.1 protein-ERM) domain and the C-terminal ERM association domain (C-ERMAD). The FERM domain and the C-ERMAD can bind to each other in a head-to-tail manner, leading to a closed/inactive conformation. Typically, phosphorylation on the C-terminus Thr has been associated with the activation of ERMs, including secretion from macrophages and platelets. It has previously been shown that the ability of the so-called mast cell "stabilizer" disodium cromoglycate (cromolyn) to inhibit secretion from rat mast cells closely paralleled the phosphorylation of a 78 kDa protein, which was subsequently shown to be moesin, a member of ERMs. Interestingly, the phosphorylation of moesin during the inhibition of mast cell secretion was on the N-terminal Ser56/74 and Thr66 residues. This phosphorylation pattern could lock moesin in its inactive state and render it inaccessible to binding to the Soluble NSF attachment protein receptors (SNAREs) and synaptosomal-associated proteins (SNAPs) critical for exocytosis. Using confocal microscopic imaging, we showed moesin was found to colocalize with actin and cluster around secretory granules during inhibition of secretion. In conclusion, the phosphorylation pattern and localization of moesin may be important in the regulation of mast cell secretion and could be targeted for the development of effective inhibitors of secretion of allergic and inflammatory mediators from mast cells.

Quercetin is more effective than cromolyn in blocking human mast cell cytokine release and inhibits contact dermatitis and photosensitivity in humans

Mast cells are immune cells critical in the pathogenesis of allergic, but also inflammatory and autoimmune diseases through release of many pro-inflammatory cytokines such as IL-8 and TNF. Contact dermatitis and photosensitivity are skin conditions that involve non-immune triggers such as substance P (SP), and do not respond to conventional treatment. Inhibition of mast cell cytokine release could be effective therapy for such diseases. Unfortunately, disodium cromoglycate (cromolyn), the only compound marketed as a mast cell "stabilizer", is not particularly effective in blocking human mast cells. Instead, flavonoids are potent anti-oxidant and anti-inflammatory compounds with mast cell inhibitory actions. Here, we first compared the flavonoid quercetin (Que) and cromolyn on cultured human mast cells. Que and cromolyn (100 µM) can effectively inhibit secretion of histamine and PGD(2). Que and cromolyn also inhibit histamine, leukotrienes and PGD(2) from primary human cord blood-derived cultured mast cells (hCBMCs) stimulated by IgE/Anti-IgE. However, Que is more effective than cromolyn in inhibiting IL-8 and TNF release from LAD2 mast cells stimulated by SP. Moreover, Que reduces IL-6 release from hCBMCs in a dose-dependent manner. Que inhibits cytosolic calcium level increase and NF-kappa B activation. Interestingly, Que is effective prophylactically, while cromolyn must be added together with the trigger or it rapidly loses its effect. In two pilot, open-label, clinical trials, Que significantly decreased contact dermatitis and photosensitivity, skin conditions that do not respond to conventional treatment. In summary, Que is a promising candidate as an effective mast cell inhibitor for allergic and inflammatory diseases, especially in formulations that permit more sufficient oral absorption.

Mast cells and cutaneous malignancies

This paper reviews the role of mast cells in the development and progression of basal cell carcinoma, squamous cell carcinoma and malignant melanoma. Mast cells accumulate around cutaneous malignancies. Current evidence suggests that mast cells contribute to the tumorigenesis of cutaneous malignancies through four mechanisms. (1) Immunosuppression: Ultraviolet-B radiation, the most important initiator of cutaneous malignancies, activates mast cells. Upon irradiation of the skin, trans-urocanic acid in the epidermis isomerizes to cis-urocanic acid, which stimulates neuropeptide release from neural c-fibers. These neuropeptides in turn trigger histamine secretion from mast cells, leading to suppression of the cellular immune system. (2) Angiogenesis: Mast cells are the major source of vascular endothelial growth factor in basal cell carcinoma and malignant melanoma. Vascular endothelial growth factor is one of the most potent angiogenic factors, which also induces leakage of other angiogenic factors across the endothelial cell wall into the matrix. Mast cell proteases reorganize the stroma to facilitate endothelial cell migration. As well, heparin, the dominant mast cell proteoglycan, assists in blood-borne metastasis. (3) Degradation of extracellular matrix: Through its own proteases, and indirectly via interaction with other cells, mast cells participate in degradation of the matrix, which is required for tumor spread. (4) Mitogenesis: Mast cell mediators including fibroblast growth factor-2 and interleukin-8 are mitogenic to melanoma cells. Current evidence supports an accessory role for mast cells in the development and progression of cutaneous malignancies. Emerging data, however, also suggest that mast cells might, in fact, have opposing roles in tumor biology, and the microenvironment could polarize mast cells to possess either promoting or inhibitory effects on tumors.

Gallic Acid Inhibits Histamine Release and Pro-inflammatory Cytokine Production in Mast Cells

The discovery of drugs for the treatment of inflammatory allergic diseases such as, asthma, allergic rhinitis, and sinusitis is a very important subject in human health. Gallic acid (3,4,5-trihydroxybenzoic acid), a polyphenyl natural products from gallnut and green tea, is known to have anti-oxidant, anti-inflammatory, anti-microbial, and radical scavenging activities. The aim of the present study was to elucidate whether gallic acid modulates the inflammatory allergic reaction and to study its possible mechanisms of action. Gallic acid attenuated compound 48/80- or immunoglobulin E (IgE)-induced histamine release from mast cells. The inhibitory effect of gallic acid on the histamine release was mediated by the modulation of cAMP and intracellular calcium. Gallic acid decreased the phorbol 12-myristate 13-acetate plus calcium ionophore A23187-stimulated pro-inflammatory cytokine gene expression and production such as TNF-alpha and IL-6 in human mast cells. The inhibitory effect of gallic acid on the pro-inflammatory cytokine was nuclear factor-kappaB and p38 mitogen-activated protein kinase dependent. In addition, gallic acid inhibited compound 48/80-induced systemic allergic reaction and IgE-mediated local allergic reaction. The inhibitory activity of gallic acid on the allergic reaction and histamine release was found to be similar with disodium cromoglycate. Our findings provide evidence that gallic acid inhibits mast cell-derived inflammatory allergic reactions by blocking histamine release and pro-inflammatory cytokine expression, and suggest the mechanisms of action. Furthermore, in vivo and in vitro anti-allergic effect of gallic acid suggests a possible therapeutic application of this agent in inflammatory allergic diseases.

Critical role of mast cells in inflammatory diseases and the effect of acute stress

Mast cells are not only necessary for allergic reactions, but recent findings indicate that they are also involved in a variety of neuroinflammatory diseases, especially those worsened by stress. In these cases, mast cells appear to be activated through their Fc receptors by immunoglobulins other than IgE, as well as by anaphylatoxins, neuropeptides and cytokines to secrete mediators selectively without overt degranulation. These facts can help us better understand a variety of sterile inflammatory conditions, such as multiple sclerosis (MS), migraines, inflammatory arthritis, atopic dermatitis, coronary inflammation, interstitial cystitis and irritable bowel syndrome, in which mast cells are activated without allergic degranulation.

Ca2+ and phorbol ester effect on the mast cell phosphoprotein induced by cromolyn

Several phosphoproteins are involved in stimulus-secretion coupling. The beta and gamma subunits of immunoglobulin E binding protein (FC epsilonRI) and three other protein bands get phosphorylated during stimulation of mast cell secretion. These additional proteins of 42, 59 and 68 kDa are also phosphorylated when secretion is stimulated by compound 48/80 (C48/80). A 78 kDa band, however, is phosphorylated as secretion wanes after stimulation with C48/80 and by the anti-allergic drug disodium cromoglycate (cromolyn). Phosphorylation was blocked by protein kinase C inhibitors. We investigated the isozyme involved by first showing that a cation ionophore prevented the phosphorylation of the 78 kDa protein, while a Ca2+ chelator did not affect phosphorylation even though it enhanced the inhibitory effect of cromolyn. This protein was identified as moesin by immunoprecipitation. Protein kinase C activators had no effect on 78 kDa protein phosphorylation either in the presence or absence of Ca2+ ions, but prevented its phosphorylation by cromolyn. Protein phosphatase inhibitors prolonged the duration, but not the amount of phosphate incorporated in the 78 kDa protein band while cromolyn had no effect on protein phosphatase action in vitro. The insensitivity of the 78 kDa protein phosphorylation to calcium and protein kinase C activators suggests that an atypical protein kinase C isozyme may be involved. Western blot analysis identified the presence of isozymes alpha, beta, delta and zeta, of which only the latter fits the profile suggested by the present findings.

Inhibition of cromolyn-induced phosphorylation of a 78-kDa protein by phorbol esters in rat peritoneal mast cells

Disodium cromoglycate (cromolyn) is a well documented inhibitor of immunologically-induced histamine release from rat peritoneal mast cells and has been shown to stimulate the phosphorylation of a mast cell protein of apparent molecular mass 78,000 Da (78 kDa), an event which may be involved in terminating secretion. Here we aimed to determine the role of the ubiquitous enzyme, protein kinase C, in the phosphorylating activity of cromolyn by examining the effects of phorbol esters (activators of protein kinase C) on protein phosphorylation in [32P]orthophosphate loaded rat peritoneal mast cells. Protein kinase C-activating phorbol esters such as 12-O-tetradecanoyl phorbol-13-acetate (TPA) and 4beta-phorbol 12,13-dibutyrate (PdBu) were found to potently inhibit cromolyn-induced phosphorylation when added to mast cells simultaneously with cromolyn (IC50 22 and 79 nM respectively). 4Alpha-phorbol 12,13-didecanoate (PdD), a phorbol ester which does not activate protein kinase C, had no effect on cromolyn-induced phosphorylation. Addition of TPA to mast cells previously exposed to cromolyn for 60 sec (i.e. when 78-kDa protein phosphorylation is maximal) also caused a very rapid dephosphorylation of the 78-kDa protein. Phosphorylation of the 78-kDa protein can also be induced by dibutyryl cyclic GMP and this action was similarly inhibited by TPA and PdBu. Cromolyn inhibited secretion induced by anti-IgE, but not by TPA, and thus inhibition of secretion by cromolyn is further correlated to its phosphorylation of the 78-kDa protein. The data suggest that the inhibitory action of cromolyn on mast cell secretion and phosphorylation of the 78-kDa protein are not mediated through a phorbol ester-sensitive protein kinase C, but more likely that such an enzyme could be involved in regulating dephosphorylation of the 78-kDa protein. Further explanations for this novel dephosphorylating activity of phorbol esters are discussed.

Influence of interleukin-1 receptor antagonist on [3H]serotonin and histamine release by rat basophilic leukemia-2H3 cells

Mast cells located in connective tissues are a potent source of vasoactive and inflammatory mediators, such as cytokines. They accumulate in tissues in a wide variety of diseases where their function in most cases in unclear. In this report we provide evidence that rat basophilic leukemia cells (RBLC) cultured with a natural inhibitor of IL-1, interleukin-1 receptor antagonist (IL-1RA) (500 ng/ml) for 48 h, strongly inhibited the spontaneous release of serotonin (5HT) (from 25.2 to 29.9%), and histamine (from 22.50 to 43.49%), compared to untreated cells (control). When IL-IRA-treated and -untreated RBLC were stimulated with a secretagogue (anti-IgE), no difference was found in the percent of 5HT and histamine release. The present studies describe an additional biological activity of IL-1RA, inhibiting histamine and 5HT spontaneous release from RBLC cultures.

Characterization of the 78 kDa mast cell protein phosphorylated by the antiallergic drug cromolyn and homology to moesin

Mast cells (MC) can be stimulated to secrete by cross-linking immunoglobulin E bound to specific surface receptors, as well as in response to polycationic molecules such as substance P and compound 48/80. The antiallergic drug disodium cromoglycate (cromolyn) inhibited MC secretion and rapidly incorporated phosphate into a 78 kDa protein, speculated to be its mode of action. This protein was purified by single and two-dimensional gel electrophoresis, and was shown to be phosphorylated primarily on serine residues by protein kinase C. Partial amino acid sequencing of two generated fragments was identical to that of portions of mouse moesin, a member of the band 4.1 superfamily of proteins, with no definitive function known to date. Polyclonal antibodies raised against the rat basophil leukemia cell moesin cDNA expressed in Escherichia coli immunoprecipitated the 78 kDa phosphoprotein quantitatively, and immunocytochemistry localized it to the plasma membrane. Reversible phosphorylation of this 78 kDa phosphoprotein could affect its possible cytoskeletal binding through which it may regulate stimulus-secretion coupling in MC.

Effect of interleukin-1 receptor antagonist (IL-1RA) on histamine and serotonin release by rat basophilic leukemia cells (RBL-2H3) and peritoneal mast cells

Recently, it has been appreciated that cultured mast cells are significant sources of cytokines. However, the role of interkeukin-1 (IL-1) on mast cells and/or basophil degranulation is still unclear. In this report we provide evidence that rat basophilic leukemia cells (RBLC) cultured with a natural inhibitor of IL-1, interleukin-1 receptor antagonist (IL-1RA) (500 ng/ml) for 48 h, strongly inhibited the spontaneous release of serotonin (5HT) and histamine (from 22.50 to 43.49%), compared to untreated cells (control). When IL-1RA-treated and untreated RBLC were stimulated with a secretagogue (anti-IgE), no difference was found in the percent of 5HT and histamine release. Moreover, in another set of experiments using rat peritoneal mast cells (RPMC) treated and untreated with IL-1RA, we found that IL-1RA did not affect the release of 5HT or histamine, even when the secretagogue anti-IgE or compound 48/80 (C48/80) were used. The present studies describe an additional biological activity of IL-1RA, inhibiting histamine and 5HT release from RBLC cultures.

Cortical changes in starfish (Asterina pectinifera) oocytes during 1-methyladenine-induced maturation and fertilisation/activation

Maturation of the starfish oocyte cortex to produce an effective cortical granule reaction and fertilisation envelope is believed to develop in three phases: (1) pre-methyladenine (1-MA) stimulation; (2) post-1-MA stimulation, pregerminal vesicle breakdown; and (3) post-germinal vesicle breakdown. The present study was initiated to identify what each of these phases may encompass, specifically with respect to structures associated with the oocyte cortex, including cortical granules, microvilli and vitelline layer. 1-MA treatment brought about an orientation of cortical granules such that they became positioned perpendicular to the oocyte surface, and an approximately 4-fold decrease in microvillar length. A-23187 activation of immature oocytes treated with (10 min; pregerminal vesicle breakdown) or without 1-MA resulted in a reduction in cortical granule number of 21% and 41%, respectively (mature oocytes underwent a 96% reduction in cortical granules). Elevation of the fertilisation envelope in both cases was significantly retarded compared with activated mature oocytes. In activated mature oocytes, the vitelline layer elevated 20.0 +/- 5.4 mu m from the egg's surface, whereas in immature oocytes treated with just A-23187 or with 1-MA (10 min) and A-23187, it lifted 0.35 +/- 0.1 and 0.17 +/- 0.04 mu m, respectively. The fertilisation envelopes of activated (or fertilised) immature oocytes also differed morphologically from those of mature oocytes. In activated, immature oocytes, the fertilisation envelope was not uniform in its thickness and possessed thick and thin regions as well as fenestrations. Additionally, it lacked a complete electron-dense stratum that characterised the fertilisation envelopes of mature oocytes. The nascent perivitelline space of immature oocytes was also distinguished by the presence of numerous vesicles which appeared to be derived from microvilli. Differences in the morphology of cortices from activated (fertilised) and non-activated, immature and mature oocytes substantiate previous investigations demonstrating three phases of cortical maturation, and are consistent with physiological changes that occur during oocyte maturation, involving ionic conductance of the plasma membrane, establishment of slow and fast blocks to polyspermy and elevation of a fertilisation envelope.

Effect of a potent selective protein kinase C inhibitor on histamine release from rat mast cells

3,10-Dihydroxy-10-[(dimethylamino)methyl]-2,3,9,10,11,12-hexahydro-9- methyl-9,12-epoxy-1H-diindolo[1,2,3-fg-3',2',1'-k1]pyrrolo[3,4- l][1,6]benzodiazocin-1-one (UCN-01) strongly and dose-dependently inhibited histamine release from rat peritoneal mast cells that was induced by anti-immunoglobulin E (anti-IgE), calcimycin (A 23187), and 1,2-o-tetradecanoyl-13-acetate (TPA). The concentrations of UCN-01 required for 50% inhibition of histamine release induced by anti-IgE, A23187, and TPA were 1.5, 2.7, and 1.4 nM, respectively; these values are similar to those for 50% inhibition of protein kinase C. These results suggest possible participation cells induced by various secretagogues.

MY-1250, a major metabolite of the anti-allergic drug repirinast, induces phosphorylation of a 78-kDa protein in rat mast cells

Repirinast (MY-5116; isoamyl 5,6-dihydro-7,8-dimethyl-4,5-dioxo-4H-pyrano [3,2-c]quinoline-2-carboxylate) is an anti-allergic drug of demonstrated effectiveness for treating bronchial asthma in humans. MY-1250 (5,6-dihydro-7,8-dimethyl-4,5-dioxo-4H-pyrano [3,2-c]quinoline-2-carboxylic acid), the major active metabolite of repirinast, inhibits antigen-induced histamine release from sensitized rat peritoneal exudate cells (PEC). When purified rat mast cells were treated with MY-1250 (2.5 x 10(-5) M) for 1 min, phosphorylation of a specific mast cell protein of apparent molecular mass of 78 kDa was observed as previously reported for sodium cromoglycate (SCG). Phosphorylation of this protein induced by MY-1250 and SCG occurred in a concentration-dependent manner with IC50 values of 2.0 x 10(-7) and 1.4 x 10(-5) M, respectively. MY-1250 did not inhibit calcium ionophore A23187 (1 microgram/mL)-induced histamine release from rat PEC. In the presence of calcium ionophore A23187 (1 microgram/mL), phosphorylation of this protein induced by MY-1250 was not evident. In conclusion, MY-1250 induced phosphorylation of a 78-kDa protein in rat mast cells and MY-1250 may inhibit histamine release by regulating phosphorylation of this protein in rat mast cells.

Identification of vimentin in rat peritoneal mast cells and its phosphorylation in association with histamine release

Stimulation of rat peritoneal mast cells with histamine releasers, such as compound 48/80 and substance P, caused a similar pattern of protein phosphorylations: the molecular weights of the two major phosphorylated proteins were 45 kDa and 59 kDa. When rat mast cells permeabilized with beta-escin were exposed to Ca2+ at concentrations higher than 0.6 microM, phosphorylated proteins of identical molecular weight were also detected. By a radioimmunoprecipitation assay using anti-vimentin mouse monoclonal antibody, the 59 kDa protein was identified as vimentin, one of the intermediate cytoskeletal proteins. Moreover, it became apparent that the phosphoamino acid in phosphorylated vimentin was a serine residue. Sequential changes in vimentin phosphorylation were similar to that of histamine release elicited by histamine releasers: phosphorylation took place within 5 s of stimulation and reached a maximum within 10 s. When permeabilized mast cells were treated with calphostin C, a specific protein kinase C inhibitor, phosphorylation was markedly inhibited. Fluorescence images of mast cells stained with FITC-labelled anti-vimentin antibody showed filamentous structures surrounding the granules in the cytoplasm. However, after exposure to compound 48/80, the filamentous structures promptly disappeared and a dim fluorescence was observed homogeneously in the cell indicating that a rapid depolymerization of vimentin had taken place. From the present study, it became clear that when rat peritoneal mast cells were stimulated, vimentin was rapidly phosphorylated by protein kinase C and this phosphorylation process seems to be related to histamine release.

Effects of flavonoids on immune and inflammatory cell functions

No doubt can remain that the flavonoids have profound effects on the function of immune and inflammatory cells as determined by a large number and variety of in vitro and some in vivo observations. That these ubiquitous dietary chemicals may have significant in vivo effects on homeostasis within the immune system and on the behavior of secondary cell systems comprising the inflammatory response seems highly likely but more work is required to strengthen this hypothesis. Ample evidence indicates that selected flavonoids, depending on structure, can affect (usually inhibit) secretory processes, mitogenesis, and cell-cell interactions including possible effects on adhesion molecule expression and function. The possible action of flavonoids on the function of cytoskeletal elements is suggested by their effects on secretory processes. Moreover, evidence indicates that certain flavonoids may affect gene expression and the elaboration and effects of cytokines and cytokine receptors. How all of these effects are mediated is not yet clear but one important mechanism may be the capacity of flavonoids to stimulate or inhibit protein phosphorylation and thereby regulate cell function. Perhaps the counterbalancing effect of cellular protein tyrosine phosphatases will also be found to be affected by flavonoids. Some flavonoid effects can certainly be attributed to their recognized antioxidant and radical scavenging properties. A potential mechanism of action that requires scrutiny, particularly in relation to enzyme inhibition, is the redox activity of appropriately configured flavonoids. Finally, in a number of cell systems it seems that resting cells are not affected significantly by flavonoids but once a cell becomes activated by a physiological stimulus a flavonoid-sensitive substance is generated and interaction of flavonoids with that substance dramatically alters the outcome of the activation process.

Role of Ca2+/phospholipid-dependent protein kinase in catecholamine secretion from bovine adrenal medullary chromaffin cells

The role of Ca2+/phospholipid-dependent protein kinase (protein kinase C) in catecholamine secretion from bovine adrenal medullary chromaffin cells was examined using four protein kinase C inhibitors: polymyxin B, sphingosine, staurosporine, and 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7). For this purpose, digitonin-permeabilized chromaffin cells were used. Secretion of catecholamines from these cells was stimulated by the addition of micromolar amounts of exogenous free Ca2+. 12-O-Tetradecanoylphorbol-13-acetate (TPA) and arachidonic acid, activators of protein kinase C, enhanced the catecholamine secretion evoked by Ca2+. But phorbol-12, 13-diacetate, a phorbol ester analog that does not activate protein kinase C, had no effect on Ca2(+)-evoked secretion. Polymyxin B at a low concentration (1 microM) abolished the enhancement of secretion by TPA or arachidonic acid without affecting the secretion evoked by Ca2+. However, polymyxin B at higher concentrations (10-100 microM) greatly reduced Ca2+-evoked catecholamine secretion. Sphingosine 10 microM-1 mM), Staurosporine (100 nM-1 microM, and H-7 (100-500 microM) inhibited TPA- or arachidonic acid-enhanced secretion but not Ca2(+)-evoked secretion. In cells in which protein kinase C was down-regulated by TPA, specific binding of [3H]phorbol-12,13-dibutyrate to the cells almost disappeared and the enhancement of secretion by TPA was no longer observed, whereas Ca2(+)-evoked secretion was maintained. These results strongly suggest that protein kinase C is not essential for the Ca2(+)-dependent catecholamine secretion from bovine adrenal chromaffin cells, but acts instead as a modulator.

Mast cell heterogeneity: two-dimensional gel electrophoretic analyses of rat peritoneal and intestinal mucosal mast cells

Peritoneal mast cells (PMC) and intestinal mucosal mast cells (IMMC) were purified from rats infected with the nematode Nippostrongylus brasiliensis. Overall protein constituents of both mast cell subtypes were analyzed by two-dimensional gel electrophoresis using either nonequilibrium pH gradient electrophoresis (NEPHGE) or isoelectric focusing (IEF) in the first dimension and SDS-PAGE (10%) in the second dimension followed by silver staining. PMC had seven dominant basic proteins (PB2-8; pI 9-9.5) with estimated molecular masses of 26 to 37 kDa, as well as 80 to 90 neutral or acidic proteins, most of which had pI 6 to 7.5 and estimated molecular masses of 20 to 100 kDa. All the basic proteins were granule-associated. Three basic proteins, PB6 (29 kDa), PB7 (28 kDa) and PB8 (RMCP I, 26 kDa), bound [3H]diisopropyl fluorophosphate (DFP), suggesting that they are serine proteases. However, only PB8 was reactive with antibodies to RMCP I. Another basic component (less than 14 kDa), perhaps a degradation product of PB6, PB7 or PB8, also bound [3H]DFP. By comparison, IMMC possessed nine basic proteins (IB1-9) and, in general, they were more acidic (pI about 8.5-9) than those of PMC. Four major basic proteins (IB6-9) were all 24 kDa but were slightly different in isoelectric points. These and another 46-kDa basic component (IB2) were reactive with antibodies to RMCP II and bound [3H]DFP. There were no other DFP-binding proteins in IMMC. In spite of remarkable differences between basic granule-associated proteins in PMC and basic proteins in IMMC, spots in the neutral-acidic range were for the most part similar in the two mast cell subsets, although quantitative differences were evident for some spots. Thus, rat mast cell populations from the peritoneal cavity and intestinal mucosa exhibit marked heterogeneity in their protein constituents with basic pI, including in their granule-associated proteins with serine protease activity.

A 42-kD tyrosine kinase substrate linked to chromaffin cell secretion exhibits an associated MAP kinase activity and is highly related to a 42-kD mitogen-stimulated protein in fibroblasts

The localization of the protein tyrosine kinase pp60c-src to the plasma membrane and to the membrane of secretory vesicles in neurally derived bovine chromaffin cells has suggested that tyrosine phosphorylations may be associated with the process of secretion. In the present study we have identified two cytosolic proteins of approximately 42 and 45 kD that become phosphorylated on tyrosine in response to secretagogue treatment. Phosphorylation of these proteins reached a maximum (3 min after stimulation) before maximum catecholamine release was observed (5-10 min after stimulation). Both secretion and tyrosine phosphorylation of p42 and p45 required extracellular Ca2+. Tyrosine-phosphorylated proteins of similar Mr have previously been identified in 3T3-L1 adipocytes stimulated with insulin (MAP kinase; Ray, L. B., and T. W. Sturgill. 1987. Proc. Natl. Acad. Sci. USA. 84:1502-1506) and in avian and rodent fibroblasts stimulated with a variety of mitogenic agents (Cooper, J. A., D. F. Bowen-Pope, E. Raines, R. Ross, and T. Hunter. 1982. Cell. 31:263-273; Nakamura, K. D., R. Martinez, and M. J. Weber. 1983. Mol. Cell. Biol. 3:380-390). Comparisons of the secretion-associated 42-kD protein of chromaffin cells with the 42-kD protein of Swiss 3T3 fibroblasts and 3T3-L1 adipocytes provide evidence that these three proteins are highly related. This evidence includes comigration during one-dimensional SDS-PAGE, cochromatography using ion exchange and hydrophobic matrices, similar isoelectric points, identical cyanogen-bromide peptide maps, and cochromatography of MAP kinase activity with the tyrosine-phosphorylated form of pp42. This protein(s), which appears to be activated in a variety of cell types, may serve a common function, perhaps in signal transduction involving a cascade of kinases.

Modulation of pp60c-src tyrosine kinase activity during secretion in stimulated bovine adrenal chromaffin cells

High levels of the proto-oncogene product, pp60c-src, have been found in developing and adult neural tissues as well as in certain fully mature cells of the hematopoietic lineage, e.g., platelets and myelomonocytes. Adrenal medullary chromaffin cells exhibit characteristics of both types of cells, i.e., they are derived from the neural crest and carry out exocytosis in response to specific stimuli. Earlier studies have shown that pp60c-src localizes not only to the plasma membrane of chromaffin cells but also to the membranes of chromaffin granules, the secretory vesicles of these cells that store catecholamines and other secretory products. To investigate the possible involvement of pp60c-src in exocytosis, cultured bovine chromaffin cells were analyzed for changes in c-src tyrosine kinase activity in response to stimulation by several secretagogues. Results of in-vitro immune complex kinase assays showed that pp60c-src, derived from cells that had been stimulated for various lengths of time, exhibited decreased auto- and transphosphorylating activities as compared to pp60c-src immunoprecipitated from control cells. The greatest reduction in activity was observed 10 min post-stimulation, while normal levels were regained 2-6 hr after secretagogue treatment. Western immunoblot analysis of the immunoprecipitated pp60c-src revealed that approximately 50% less c-src protein was present in immune complexes prepared 10 min after stimulation as compared to those prepared from mock-stimulated controls, resulting in a specific autophosphorylating activity that was 42-47% of control and little or no reduction in the transphosphorylating specific activity. In experiments in which the rate of secretion of [3H]-norepinephrine from cells preloaded with this compound was compared to the rate of modulation of pp60c-src activity, 50% of the maximal reduction in pp60c-src activity occurred within 2-4 min while 50% maximal release of [3H]-norepinephrine occurred within 1-3 min. Taken together, these results suggest that pp60c-src may play some role (direct or indirect) in the exocytotic process.

Enhancement of the phosphorylation of membrane bound myosin light chain by antigen stimulation in rat basophilic leukemia cells

We have found that phosphorylation of the 18,000 mol. wt protein in rat basophilic leukemia cells (RBL-2H3 cells) is enhanced by stimulation by an antigen. This phenomenon was also observed when cells were treated with phorbol myristate (TPA) and a calcium ionophor, A23187. The phosphorylated 18,000 mol. wt protein was mainly located in the membrane fraction. It was identified as one of the myosin light chains as follows: (1) the mol. wt of one of the major myosin light chains of RBL-2H3 cells was 18,000; (2) more than half of the phosphorylated 18,000 mol. wt protein was recovered in an actomyosin fraction; (3) this phosphorylated 18,000 mol. wt protein was immunoprecipitated with anti-myosin antibody. Since the presence of Ca2+ in the cell culture medium was essential for the phosphorylation of the 18,000 mol. wt protein and, since trifluoperazine (a potent inhibitor of calmodulin as well as of the degranulation process of RBL-2H3 cells) inhibited the reaction, the phosphorylation may be catalyzed by a Ca2+-calmodulin-dependent process, most likely by myosin light chain kinase. These results, together with our previous observation [Teshima et al. Molec Immun. 23, 279-284 (1986)], suggest that simultaneous phosphorylation of the 18,000 mol. wt myosin light chain and a 36,000 mol. wt membranous protein is a prerequisite for the degranulation of RBL-2H3 cells.

Inhibition of human platelet secretion and of Ca2+, calmodulin-dependent protein phosphorylation by the antiallergic agent GMCHA

Calcium ion-dependent interaction with purified calmodulin (CaM), of a potent inhibitor of histamine release from mast cells, trans-4-guanidinomethylcyclohexanecarboxylic acid p-tertbutylphenylester (GMCHA), was investigated using 5-(dimethylamino)-1-naphthalenesulfonyl-calmodulin (dansyl-CaM). GMCHA undergoes a fluorescence increase with the Ca2+-dansyl-CaM complex but there is no significant change in the dansyl-CaM fluorescence with GMCHA, up to a 10 microM in the absence of calcium ion. This suggests that binding of GMCHA to CaM is Ca2+-dependent on the apparent Kd is approximately 1 microM. GMCHA suppressed the fluorescence of the hydrophobic probe 8-anilino-1-naphthalenesulfonate (ANS), in the presence of the Ca2+-CaM complex, with an IC50 value of 3 microM. [3H]N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7) bound to the purified CaM was displaced, in a concentration dependent manner by GMCHA, the Ki value of GMCHA against the binding of W-7 to CaM was 2.3 microM, and there was a selective inhibition of the Ca2+-CaM induced activation of enzymes such as myosin light chain kinase. Increasing the CaM concentration in the presence of Ca2+ overcame the GMCHA-induced inhibition of myosin light chain kinase activation, with a Ki value of 2.7 microM. GMCHA at these concentrations is effective in inhibiting the release of histamine from mast cells. Moreover, this compound suppresses platelet secretion and relaxes vascular strips, at concentrations similar to those seen with the CaM interacting action and characteristic of CaM antagonists such as W-7. GMCHA also inhibits the Ca2+, CaM-dependent myosin light chain phosphorylation of human platelets. These results suggest that GMCHA, a potent inhibitor of histamine release from mast cells, suppresses platelet secretion, relaxes vascular smooth muscle and inhibits Ca2+, CaM-dependent protein phosphorylation, all at similar concentrations.

Persistence of early crosslink-dependent signal transduction events in human basophils after desensitization

Desensitization of human basophils with anti-IgE antibody or antigen induced an increased sensitivity to the phorbol ester TPA, evidenced as 2-5 fold increase in the potency of TPA to induce histamine release. As noted in previous publications the magnitude of the change in sensitivity to TPA was a function of the extent of cell surface IgE crosslinking. Thus, the density of cell surface antigen-specific IgE determined the magnitude of the curve shift and the multivalent antigen, BPO21-HSA was found to produce a greater curve shift than the simpler bivalent hapten, BPO2, in accord with previous studies which demonstrated that BPO2 was a "weak" stimulus compared to BPO21-HSA. Basophils which had been fully desensitized by prior treatment with anti-IgE or antigen in the absence of calcium also displayed the curve shift for at least 24 h after desensitization. However, the change induced by crosslinking which altered the cells' sensitivity to TPA required the continued presence of crosslinks and was therefore not the result of a permanent alteration induced by desensitization. Basophils which were fully desensitized to BPO7-HSA demonstrated the curve shift provided that the antigen-induced crosslinks were maintained: treatment with monovalent hapten, BPO-EACA, rapidly returned the cell response to TPA to control, non-desensitized, levels. Since TPA is thought to act by activation of protein kinase C (PKC) we demonstrated that BPO-HSA induced crosslinking increased PKC activity and that the increased activity persisted unless antigen-induced crosslinks were dissociated by the addition of monovalent hapten.(ABSTRACT TRUNCATED AT 250 WORDS)

Release of gonadotropin alpha subunit from rat pituitary cultures in response to GnRH

Gonadotropin releasing hormone (GnRH)-stimulated release of the alpha subunit common to the gonadotropins and to thyrotropin was studied in rat pituitary cell cultures. In these studies we took advantage of a recently prepared antiserum specific for the alpha subunit. We show that pituitary cells treated with GnRH released alpha subunit in a similar pattern to intact luteinizing hormone (LH) during short-term incubations (0-12 h); during prolonged incubations (12-48 h), however, release of alpha subunit did not desensitize in response to the releasing hormone and the pattern became different from that measured for intact LH. Further, we assessed the relative requirement for Ca2+ in the release of LH and alpha subunit. When pituitary cells were treated with 10(-8) M GnRH in the presence of a range of concentrations of the Ca2+ ion channel antagonist, methoxyverapamil (D-600), release of both LH and alpha subunit was inhibited in a similar and dose-dependent manner; 10(-4) M D-600 showed maximum inhibitory efficacy (IC50 = 10(-5) M). The calmodulin antagonist, pimozide, also inhibited both GnRH-stimulated LH and alpha subunit release (IC50 = 0.75 microM). These data suggested that although the Ca2+/calmodulin system appears to mediate both the release of LH and alpha subunit in response to GnRH, these processes appear differentially regulated during long-term exposure to the releasing hormone.

Stimulation of murine cultured mast cells under anaerobic conditions: inhibition of arachidonic acid release

The exocytosis of beta-hexosaminidase from either IgE-antigen- or calcium ionophore A23187-stimulated murine bone-marrow-derived mast cells was not affected by oxygen-depleted conditions regardless of the absence of glucose from the medium. No detectable changes in the content of ATP were observed when the cells were triggered immunologically under anaerobic conditions in the absence of glucose in the medium. Depletion of oxygen from mast cells activated by both stimuli almost completely inhibited the specific release of arachidonic acid, which indicates that arachidonate does not play a significant role in the secretion of preformed mediators.

Energy metabolism in rat mast cells in relation to histamine secretion

1. The relation between the energy metabolism and the secretory activity of rat peritoneal mast cells has been studied by determination of the cellular content of ATP and the rate of lactate production reflecting the rate of ATP synthesis under various experimental conditions. Secretion of histamine was induced by the antigen-antibody reaction, the polymeric amine compound 48/80, and the divalent ionophore A23187. 2. In presence of low concentrations of metabolic inhibitors (oligomycin or antimycin A) a linear relation between the secretion of histamine induced by all three liberators and the cellular ATP content at the time of cell activation was demonstrated. This may indicate a direct link between ATP and the secretory mechanism. 3. The possibility of an increased utilization of ATP during histamine secretion was explored in mast cells exposed to metabolic inhibitors. Incubation of mast cells with 2-deoxyglucose (2-DG) decreased the ATP content of the cells, and a long-lasting and stable level of mast cell ATP was observed. This is explained by a small decrease in the rate of ATP-synthesis by 2-DG. In 2-DG-treated cells secretion of histamine in response to compound 48/80 or the antigen-antibody reaction could still occur, and the secretion is shown to be associated with a decrease of the cellular ATP level. This ATP decrease indicates that secretion occurs by an ATP-requiring mechanism, that causes an increased cellular utilization of ATP in association with the secretory response. 4. The possibility has been considered that increased cytosol concentration of calcium in association with secretion may decrease the rate of ATP-synthesis due to accumulation of calcium by the mitochondria. This possibility can be excluded by the observation that in presence of respiratory inhibitors an identical ATP decrease was found during the secretion as in the case of the glycolytic inhibitor alone. This indicates that increased utilization of ATP by the cells was related directly to the secretory response. This observation was made with all three secretagogues. 5. A quantitative evaluation of the increased amount of ATP utilized by the cells in relation to the secretory response was performed by use of metabolic inhibitors. The ATP requirement of compound 48/80-induced secretion was 0.15 pmol/10(3) cells. This was observed when the ATP-synthesis was decreased to a negligible value.(ABSTRACT TRUNCATED AT 400 WORDS)

Protein phosphorylation in rat mast cell granules. Cyclic AMP dependent phosphorylation of a 44K protein associated with broken granules

When rat mast cells are prelabeled with 32PO4 and exposed to non-immunologic or immunologic stimuli under conditions that lead to mediator release from granules, they show rapid increases in labeling of a number of high molecular weight proteins. To determine if granule membrane proteins are subject to protein phosphorylation and perhaps participate in this response, granules with intact or broken membranes were isolated from sonicated, purified rat serosal mast cells on a Percoll gradient. When the granules with broken membranes were incubated with [gamma-32P]ATP and Mg2+ in the absence of exogenous protein kinases, one major radioactive band was recovered in the 44K area after electrophoresis in sodium dodecyl sulfate/polyacrylamide gels. The phosphorylation reaction with ATP required Mg2+, was enhanced by 0.05 to 0.5 microM cyclic AMP, and was inhibited by Ca2+ (0.5 mM and higher). The initial reaction was rapid, and the maximal response was seen at 30 degrees. The 44K band was absent in granules with intact membranes incubated with [gamma-32P]ATP but present when intact granules were lysed with distilled water before adding the [gamma-32P]ATP. These observations indicate that granules have an endogenous phosphorylating system and that the phosphorylation response is on the inner surface of the granule membranes. The possibility was not excluded that a portion of the phosphorylating activity was derived from the cytosol and became firmly associated with broken granules when the intact cells were sonicated. Analysis for possible phosphorylated amino acids in the 44K band after acid hydrolysis showed both phosphoserine and phosphothreonine, indicating that the radioactivity was in a phosphorylated protein or glycoprotein. The 44K phosphorylated protein was made up of several components ranging in pI from approximately 7.6 to 6.6. While the identity of the phosphorylated 44K polypeptide is uncertain, one important possibility is that it is part of an autophosphorylated cAMP dependent protein kinase. The cyclic AMP dependent phosphorylating activity present in granules provides a mechanism by which the granules might respond rapidly to cyclic AMP during mediator release.

Characterization of calcium-activated, phospholipid-dependent protein kinase from rat serosal mast cells and RBL-1 cells

Evidence is presented that rat serosal mast cells and cells of the rat basophilic leukemia line, RBL-1, each contain a calcium-activated, phospholipid-dependent protein kinase. The enzymes are very similar in their activation requirements to the calcium-dependent enzymes termed protein kinase Cs in brain. The enzyme is selectively stimulated by diolein and phosphatidylserine and is inhibited by several local anesthetics. The Ka for Ca2+ is 1.0 X 10(-3) M and 1.5 X 10(-4) M in mast cells and RBL-1 cells, respectively. The enzyme in mast cells is rapidly activated and apparently changed in its intracellular distribution when intact mast cells are stimulated with 48/80, A-23187, and anti-IgE and 12-O-tetradecanoyl-13-acetate in combination.

Phosphorylation and dephosphorylation of chromaffin cell proteins in response to stimulation

Stimulation of bovine chromaffin cell in culture changed (increased or decreased) the phosphorylation state of several proteins as examined by 32P incorporation. Enhanced phosphorylation of 22 protein bands as well as increased dephosphorylation of a 20.4 kilodaltons protein band was observed when extracts of cultured chromaffin cells stimulated by either acetylcholine or high K+ were subjected to mono-dimensional gel electrophoresis. For several protein bands, the degree of phosphorylation was larger in cells stimulated by acetylcholine than in those challenged by a depolarizing concentration of K+. The most affected phosphoproteins have apparent molecular weights of 14,800, 29,000, 33,000, 57,000 (tubulin subunit), 63,000 (tyrosine hydroxylase subunit) and 94,000. The presence of a low extracellular calcium concentration (0.5 mM Ca2+ plus 15 mM Mg2+) in the incubation medium inhibited (38-100%) the acetylcholine-evoked increases in protein phosphorylation observed previously for 18 protein bands. Trifluoperazine at the concentration required for 50% inhibition of acetylcholine-induced catecholamine release decreases (33-100%) the stimulation-induced phosphorylation in all polypeptides, with the exception of the 14.8 kilodaltons and the dephosphorylated 20.4 kilodaltons components which were not affected. Two-dimensional gel electrophoresis analysis revealed that exposure of chromaffin cells to acetylcholine produced two types of effect on protein phosphorylation: activation of protein kinase activities affecting about 30 polypeptides; activation of protein phosphatase activities resulting in the dephosphorylation of about 40 polypeptides, most of them appearing as minor phosphoproteins, with the exception of the alpha-subunit of pyruvate dehydrogenase and the 20.4 kilodaltons polypeptide. On the basis of their molecular properties (molecular weight and pI) and their abundance in chromaffin cells, the 80 kilodaltons phosphoprotein which focused at pI 4.8 and the 117.5 kilodaltons phosphoprotein which focused at pI 5.0 were identified as chromogranins A and B, respectively. The relationship between acetylcholine-induced protein phosphorylation (or dephosphorylation) and catecholamine secretion was also investigated. The time course of protein phosphorylation (or dephosphorylation) paralleled or preceded [3H]noradrenaline release for 16 phosphoproteins.(ABSTRACT TRUNCATED AT 400 WORDS)

Synergistic stimulation of histamine release from rat peritoneal mast cells by 12-O-tetradecanoylphorbol 13-acetate (TPA)-type and non-TPA-type tumor promoters

Thapsigargin, a non-TPA (12-O-tetradecanoylphorbol 13-acetate)-type tumor promoter, provoked histamine release from rat peritoneal mast cells at concentrations above 30 ng/ml, but not at 10 ng/ml. TPA-type tumor promoters such as TPA, teleocidin and aplysiatoxin released very little, if any, histamine even at 100 ng/ml. When mast cells were incubated in medium containing thapsigargin at 10 ng/ml and varying concentrations of TPA-type tumor promoters, histamine release was increased synergistically. Maximum synergistic effects were observed at 10 ng/ml of each TPA-type tumor promoter. Palytoxin, another non-TPA-type tumor promoter, having no effect on histamine release at up to 10 pg/ml, also induced histamine release in the presence of 10 ng/ml of each TPA-type tumor promoter. However, no synergistic effect on histamine release was observed when mast cells were incubated in medium containing two different non-TPA-type tumor promoters, e.g., 10 ng/ml thapsigargin and 10 pg/ml palytoxin, or in medium containing two different TPA-type tumor promoters, e.g., TPA and teleocidin, TPA and aplysiatoxin, or teleocidin and aplysiatoxin (all at 10 ng/ml). These results suggest that the release of histamine from mast cells is stimulated synergistically under the mutual influence of TPA-type tumor promoters and non-TPA-type tumor promoters.

Inhibition of protein kinase activity by apomorphine

The effect of apomorphine (1-20 microM) on protein kinase activity was studied in extracts from rat peritoneal mast cells and brain tissue. Apomorphine inhibited the cyclic AMP-dependent and the calcium-plus phosphatidylserine-dependent protein kinase activity with an IC50 between 1 and 6 microM, depending on the tissue and on the protein kinase involved. This effect might explain previous results on the apomorphine-induced inhibition of histamine release in rat peritoneal mast cells.

Possible involvement of phosphorylation of a 36,000-dalton protein of rat basophilic leukemia (RBL-2H3) cell membranes in serotonin release

Phosphorylation of a 36,000-dalton (36k-Da) protein of rat basophilic leukemia (RBL-2H3) cell membranes was investigated. This phosphoprotein has been suggested to be the beta-subunit protein of the immunogloblin E (IgE) receptor of RBL-2H3 cells [Teshima et al., Biochem. biophys. Res. Commun. 125, 867-874 (1984)]. Phospholipids such as phosphatidyl serine, phosphatidyl inositol and phosphatidyl ethanolamine, which are known to be activators of protein kinase C, enhanced the phosphorylation of the 36K-Da protein. In contrast, 1-(5-isoquinoline sulfonyl)-2-methylpiperazine (H-7) which has been identified as a potent inhibitor of protein kinase C in vitro decreased incorporation of radioactive phosphate from [gamma-32P]ATP into this protein. These results indicate that the phosphorylation of the 36K-Da protein of RBL-2H3 cell membranes is catalyzed by protein kinase C. H-7 also inhibited the release of serotonin from RBL-2H3 cells stimulated with an antigen or calcium ionophore A23187 and 12-O-tetradecanoyl phorbol 13-acetate (TPA). Treatment of the antigen-stimulated cells with TPA caused a synergistic effect on the serotonin release. A similar effect was obtained by treatment of A23187-stimulated cells with TPA or 1-oleoyl-2-acetyl glycerol.

Ocular allergy and mast cell stabilizers

The role of the mast cell in ocular allergy is becoming understood. As a result, the therapeutic effects of agents that stabilize the mast cell have been evaluated in the treatment of seasonal allergic conjunctivitis, vernal keratoconjunctivitis, atopic keratoconjunctivitis, and giant papillary conjunctivitis. At present, cromolyn sodium is the only available mast cell stabilizer of known effectiveness. Clinical and laboratory investigations of the effectiveness of cromolyn sodium in the treatment of ocular allergy are reviewed in the present article.

Synchronous exocytosis in Paramecium cells involves very rapid (less than or equal to 1 s), reversible dephosphorylation of a 65-kD phosphoprotein in exocytosis-competent strains

Synchronous exocytosis in Paramecium cells involves the rapid (less than or equal to 1 s) dephosphorylation of a 65-kD phosphoprotein, which, after a lag phase of approximately 5 s, is reversed within approximately 20 s. Exocytosis inhibitors suppress this reaction; stimulatory and inhibitory effects are dose dependent. The dephosphorylation of the 65-kD phosphoprotein occurs only in exocytosis-competent strains, but not in mutant strains that cannot carry out membrane fusion, or that are devoid of secretory organelles or cannot transport them to the cell membrane. Since under all conditions analyzed the transient dephosphorylation of the 65-kD phosphoprotein strictly parallels the actual amount of exocytosed organelles, this process might be involved in exocytosis performance, perhaps in its initiation.

Calcium calmodulin and hormone secretion

As long ago as 1970, it was proposed that Ca2+ can act as a 'second messenger' like cAMP (Rasmussen & Nagata, 1979). The recognition that calmodulin is a major Ca2+ binding protein in non-muscle cells has prompted the suggestion that calmodulin may serve an analogous role for Ca2+ to that served by protein kinase for cAMP (Wang & Waisman, 1979), or at least to the regulatory subunit of the cyclic nucleotide-dependent kinases. It is becoming clear that calmodulin probably does play a role in stimulus secretion coupling in endocrine cells. Nevertheless, some of the experimental approaches which have led to this rather tentative conclusion do induce some doubts, as we have attempted to indicate. Many of the pharmacological agents used in the studies cited in this review are not specific in their interaction with calmodulin. For example, the phenothiazines also inhibit phospholipid-sensitive protein kinase. The introduction of more specific drugs, such as the naphthalene sulphonamides, may lead to a clearer picture of the role of calmodulin in hormone secretion. Relationships probably exist between cyclic nucleotides, calcium, calmodulin, phosphatidylinositol (PI) turnover and phospholipids in the overall control of the secretory process (see Fig. 1). There is considerable evidence that calcium is the primary internal signal initiating exocytosis of hormone from many glands. However, it appears that cyclic nucleotides can modulate the calcium signal either positively or negatively and it is possible that cAMP and calcium can separately activate secretion. The presence of both calmodulin-activated adenylate cyclase and cyclic nucleotide phosphodiesterase in the same tissue would appear to suggest either spatial or temporal control mechanisms or that (diagram; see text) the calcium requirement for calmodulin activation differs between the two enzymes. The true explanation is probably far more complex and involves perhaps as yet unknown factors that can differentially influence the activity of calmodulin itself in membranes and in cytosol. Berridge (1982) and Rasmussen (1980) give detailed accounts and review current hypotheses regarding relationships between the cyclic nucleotide and calcium second messenger systems. The various possible interrelationships of the putative messengers have been encompassed by the term 'Synarchic regulation' (Rasmussen, 1980). These concepts and the elucidation of the mechanisms by which cyclic AMP and calcium are involved in the control of secretion from particular cell types will make fascinating reading over the next few years.(ABSTRACT TRUNCATED AT 400 WORDS)

Differential release of serotonin without comparable histamine under diverse conditions in the rat mast cell

Pretreatment of mast cells with various psychotropic agents was shown to permit preferential release of serotonin without substantial release of histamine or massive degranulation. Differential release involved both endogenous, granule-stored serotonin, and exogenous radiolabeled serotonin that had been taken up by the cell. This phenomenon occurred in mast cells stimulated to secrete with suboptimal concentrations of the classic mast cell secretagogue compound 48/80, was associated with drugs of several different structures and known mechanisms of action, and could be inhibited by certain prostaglandins. Furthermore, differential release of serotonin occurred in mast cells of retired breeders without the use of drugs or other exogenous agents. Light microscopic studies of mast cells undergoing differential release showed minimal degranulation, indicating that most of the serotonin release did not occur via classic exocytosis. The ability of mast cell to selectively release serotonin, by a mechanism unlike that occurring in allergic anaphylactic secretion, constitutes one of the first instances of differential release from secretory cells, suggests a new mechanism of release of secretory products, and expands the potential role of mast cells in the pathophysiology of the body.