The role of calcium and cyclic adenosine 3',5'-monophosphate in the regulation of glycogen metabolism in phagocytozing human polymorphonuclear leukocytes

Role of glycogenolysis in stimulation of ATP release from cultured mouse astrocytes by transmitters and high K+ concentrations

This study investigates the role of glycogenolysis in stimulated release of ATP as a transmitter from astrocytes. Within the last 20 years our understanding of brain glycogenolysis has changed from it being a relatively uninteresting process to being a driving force for essential brain functions like production of transmitter glutamate and homoeostasis of potassium ions (K⁺) after their release from excited neurons. Simultaneously, the importance of astrocytic handling of adenosine, its phosphorylation to ATP and release of some astrocytic ATP, located in vesicles, as an important transmitter has also become to be realized. Among the procedures stimulating Ca²⁺-dependent release of vesicular ATP are exposure to such transmitters as glutamate and adenosine, which raise intra-astrocytic Ca²⁺ concentration, or increase of extracellular K⁺ to a depolarizing level that opens astrocytic L-channels for Ca²⁺ and thereby also increase intra-astrocytic Ca²⁺ concentration, a prerequisite for glycogenolysis. The present study has confirmed and quantitated stimulated ATP release from well differentiated astrocyte cultures by glutamate, adenosine or elevated extracellular K⁺ concentrations, measured by a luciferin/luciferase reaction. It has also shown that this release is virtually abolished by an inhibitor of glycogenolysis as well as by inhibitors of transmitter-mediated signaling or of L-channel opening by elevated K⁺ concentrations.

Stimulation of Ca²⁺-dependent astrocytic ATP release by glutamate, adenosine or high K⁺ concentration is abolished by inhibition of glycogenolysis, probably due to signaling inhibition. This is consistent with the K⁺-mediated pathway, but glycogenolysis-sensitive steps in the transmitter pathways are unknown.

Glycogenolysis and purinergic signaling

Both ATP and glutamate are on one hand essential metabolites in brain and on the other serve a signaling function as transmitters. However, there is the major difference that the flux in the pathway producing transmitter glutamate is comparable to the rate of glucose metabolism in brain, whereas that producing transmitter ATP is orders of magnitude smaller than the metabolic turnover between ATP and ADP. Moreover, de novo glutamate production occurs exclusively in astrocytes, whereas transmitter ATP is produced both in neurons and astrocytes. This chapter deals only with ATP and exclusively with its formation and release in astrocytes, and it focuses on potential associations with glycogenolysis, which is known to be indispensable for the synthesis of glutamate. Glycogenolysis is dependent upon an increase in free intracellular Ca(2+) concentration (Ca(2+)]i). It can be further stimulated by cAMP, but in contrast to widespread beliefs, cAMP can on its own not induce glycogenolysis. Astrocytes generate ATP from accumulated adenosine, and this process does not seem to require glycogenolysis. A minor amount of the generated ATP is utilized as a transmitter, and its synthesis requires the presence of the mainly intracellular nucleoside transporter ENT3. Many transmitters as well as extracellular K(+) concentrations high enough to open the voltage-sensitive L-channels for Ca(2+) cause a release of transmitter ATP from astrocytes. Adenosine and ATP induce release of ATP by action at several different purinergic receptors. The release evoked by transmitters or elevated K(+) concentrations is abolished by DAB, an inhibitor of glycogenolysis.

Differential regulation of early phase and late phase responses in human neutrophils by cAMP

The elevation of intracellular levels of cyclic AMP by forskolin stimulation of adenylate cyclase regulates early and late phase neutrophil responses differentially. Early phase neutrophil responses as measured by shape change in response to chemotactic factors, transmigration across a polycarbonate membrane and priming were unaffected by forskolin-induced elevation of intracellular cAMP. Late phase neutrophil responses such as release of superoxide anions, activation of phospholipase A2 and platelet activating factor (PAF) synthesis were inhibited by increasing intracellular cAMP through the addition of 10 microM forskolin for 10 min prior to stimulation. N-Formyl-methionyl-leucyl-phenylalanine-stimulated arachidonic acid release fell from 9.3% (untreated cells) to 4.6% in forskolin-treated cells. PAF generation was also inhibited from 430 pg/10(6) cells in untreated cells to background levels in forskolin-treated cells (110 pg/10(6) cells). Also, the reduction of cytochrome c by superoxide anions fell from 4.2 nmol/10(6) cells in the absence of forskolin to 2.0 nmol/10(6) cells following forskolin treatment. These results indicate that in neutrophils the elevation of cAMP acts differentially on cellular responses, not affecting early activation events, but markedly inhibiting late events such as the release of inflammatory mediators.

Inhibition of human neutrophil degranulation by forskolin in the presence of phosphodiesterase inhibitors

The secretory response of cytochalasin B-treated human polymorphonuclear neutrophils to the peptide chemoattractant f-Met-Leu-Phe (FMLP), the calcium ionophore A23187 and other secretagogues was measured by assaying neutrophil supernatants for the granular enzymes beta-glucuronidase and lysozyme. The dose-dependent enzyme secretion in response to 10(-8)-10(-4) M FMLP and A23187 was unaffected by pretreatment with 10-75 microM forskolin (an activator of adenylate cyclase), but inhibited by high concentrations of prostaglandins E1 and E2. The phosphodiesterase inhibitors isobutyl-methyl-xanthine (IBMX), papaverine and Ro 20-1724 dose dependently inhibited enzyme secretion from FMLP- or A23187-treated cells, and this effect was augmented in the presence of 50-75 microM forskolin. Similar results for PGE1, forskolin and forskolin/IBMX combinations were also obtained using leukotriene B4, platelet activating factor and C5a des-Arg as secretagogues. We conclude that the adenylate cyclase system of human neutrophils is activatable by forskolin, but that the regulatory effects of adenylate cyclase stimulants in these cells are greatly attenuated unless cyclic AMP-phosphodiesterases are inhibited. Thus the phosphodiesterase activity of neutrophils may be of functional importance and is relevant to the modulation of neutrophil activity in inflammation.

Characterization of cyclic-nucleotide phosphodiesterase activities in resting and N-formylmethionylleucylphenylalanine-stimulated human neutrophils

Cyclic nucleotide phosphodiesterase activities in human neutrophils were characterized. Neutrophil sonicates exhibited high-affinity and low-affinity cAMP phosphodiesterase activities, with apparent Km values of 1.9 microM and 112 microM, respectively. No cGMP phosphodiesterase activity was detected. Approx. 70% of cAMP phosphodiesterase activity measured at 1 microM cAMP was present in the soluble subcellular fraction, and the remainder was localized in the particulate fraction. Chromatography of the soluble subcellular fraction on DE-52 ion-exchange resin yielded a low-affinity cAMP phosphodiesterase activity and a high-affinity cAMP phosphodiesterase activity. The soluble high-affinity cAMP phosphodiesterase activity exhibited moderate calmodulin sensitivity. After incubation of intact neutrophils with N-formylmethionylleucylphenylalanine (fMet-Leu-Phe), a 25-30% increase in the activity of the high-affinity cAMP phosphodiesterase activity was observed in the sonicate and in the soluble fraction. Maximal increases were achieved after 2 min of incubation and the increases persisted for at least 10 min. The increase in activity was independent of calmodulin and guanine nucleotide regulatory proteins. These results indicate that a soluble high-affinity cAMP phosphodiesterase comprises the majority of phosphodiesterase activity in neutrophils and that increases in this activity may contribute to the regulation of cAMP levels in neutrophils during activation.

Modes of action of aspirin-like drugs

Current dogma holds that nonsteroidal anti-inflammatory drugs (NSAIDs) act by inhibition of the synthesis and release of prostaglandins. However, NSAIDs also inhibit the activation of neutrophils, which provoke inflammation by releasing products other than prostaglandins. We now report that NSAIDs (e.g., indomethacin, piroxicam) inhibit activation of neutrophils by inflammatory stimuli, such as C5-derived peptides and leukotriene B4, even when cyclooxygenase products generated in suspensions of stimulated neutrophils (prostaglandin E and thromboxanes) are present. Sodium salicylate (3 mM) greatly inhibited aggregation of neutrophils but had no effect on aggregation of platelets or production of thromboxane induced by arachidonate. Sodium salicylate and other NSAIDs also inhibit calcium movements (45Ca uptake, changes in fluorescence of chlortetracycline and quin-2). Aspirin, sodium salicylate, indomethacin, and piroxicam also enhanced the poststimulation increase in intracellular cyclic AMP. NSAIDs therefore inhibit early steps in neutrophil activation as reflected by their capacity to inhibit movements of Ca and to enhance intracellular levels of cyclic AMP.

Abnormal monocyte cytotoxicity and cyclic-AMP levels in systemic sclerosis

Monocyte antibody-dependent cell-mediated cytotoxicity (ADCC) was compared to intrinsic cyclic-adenosine-monophosphate (cAMP) levels in 14 patients with systemic sclerosis. Depressed monocyte cytotoxicity was observed. Elevated cAMP levels (2-5 times) in resting monocytes were found in 5 patients; the rest had normal cAMP values. Monocyte ADCC was inversely correlated to cellular cAMP content (r = -0.6659, P less than 0.02). Scleroderma patients with high basal cAMP levels showed impaired responses to beta-adrenergic stimulation but not to prostaglandin E (PGE1) and histamine. Patients with normal basal cAMP levels showed no defect in beta-adrenergic responses. No close correlation between monocyte abnormality and clinical state was found.

Rheumatoid arthritis. The role of neutrophil activation

Neutrophils constitute over 90% of cells found in the synovial fluid of rheumatoid arthritis (RA) patients. Since such fluids also contain immune complexes (IgG-IgG and IgG-IgM rheumatoid factors) and complement split products (C5, C5A, DES, ARG, C3B, etc.), all of the reactants are present for a local Arthus lesion. Moreover, neutrophils from RA patients endocytose these immune complexes and complement components in vivo and in vitro. In consequence, it has been suggested that lysosomal enzymes and other mediators of inflammation released by neutrophils after uptake of immune complexes (in the bulk phase or on the surface) account, at least in part, for rheumatoid inflammation. Secretion of lysosomal hydrolases, especially neutral proteases, which provoke tissue injury and generation of reactive oxygen species (e.g. O2) is part of a stimulus-secretion response to a variety of secretagogues, including immune complexes and complement components. However, the pathways of secretion and O2 generation are stimulus-specific and can be dissected to establish cause and effect relationships by (a) kinetic analysis, (b) varying the stimulus, (c) use of impermeant reagents to block discrete responses. Neutrophils also generate products of 11-cyclo-oxygenase (e.g., PGE2, TXA2) and of the 5- and 15-lipoxygenase (mono-, di and tri-hetes, LTB4 and their isomers). However, the cyclo-oxygenase products (except TXA2) do not cause inflammation acting alone; indeed, they inhibit the function of neutrophils, platelets, macrophages and mast cells. The most potent proinflammatory agent yet identified as a product of arachidonate is LTB4. LTB4 is a potent Ca ionophore, a strong chemo-attractant, induces local inflammation, and activates neutrophils.

Human leukocyte cyclic AMP and cyclic GMP levels during chemotaxis in delayed type hypersensitivity

Ten nickel-allergic patients and six healthy control subjects participated in a study of the morphology, kinetics and evolution of the cAMP and cGMP concentrations of migrated leukocytes, using an improved skin chamber technique. Also studied was the effect of nickel exposure in the chamber medium during development of an eczematous reaction in the nickel-allergic patients. Nickel exposure had a specific effect on the morphology, from the 24th hour to the end of the 48 h observation period, with a significant increase in the percentages of basophils, eosinophils and lymphocytes and a decrease of neutrophils. A significantly increased leukocyte migration rate (LMR) was observed from the 27th to 39th hour in six of the allergic patients exposed to nickel. There were no specific permanent changes in cAMP and cGMP concentrations during nickel exposure. The control chambers of the allergic patients and healthy controls had identical leukocyte morphology, LMR and leukocyte concentrations of cAMP and cGMP. However, no correlations were found between LMR, cAMP and cGMP in the eczema patients throughout the observation period.

The respiratory burst of human neutrophils treated with various stimulators in vitro is dampened by exogenous unsaturated fatty acids

Cis-unsaturated free fatty acids (FFA) at concentrations between 10 and 30 microM suppressed the superoxide respiratory burst induced in human neutrophils by the chemotactic peptide, N-formylmethionyl-leucyl-phenylalanine (FMLP). Corresponding trans-isomers had a reduced efficacy while saturated FFA were inert. The effects of unsaturated FFA were maximally achieved after several min of preincubation with cells and reversed upon washing. Increased concentrations of Ca2+ in the medium also relieved the inhibition. Unsaturated FFA were equally effective in dampening the respiratory burst induced by fluoride ions but less so with bursts elicited by 9 nM phorbol myristate acetate (PMA). Moreover reactions triggered by higher concentrations (e.g., 100 nM) of PMA were resistant to the effects of FFA. Radioimmunoassays showed that unsaturated FFA directly elevated intracellular cyclic adenosine monophosphate (cAMP) by severalfold above basal levels. It is suggested that inhibition is brought about by unsaturated FFA perturbation of the neutrophil membrane structure, perhaps with an independent contribution from a cAMP-dependent mechanism.

Effect of bovine recombinant alpha-1 interferon on inflammatory responses of bovine phagocytes

Bovine phagocytic cells (polymorphonuclear granulocytes, blood monocytes and alveolar macrophages) were treated in vitro with homogeneous, recombinant DNA produced bovine alpha-1 interferon (IFN-alpha 1). The effects seen comprised of enhanced bacterial uptake by all three cell types and increased Fc receptor activity in alveolar macrophages, inhibition of both directed and random migration of monocytes and polymorphs, increased enzyme release or inactivation, increased hydrogen peroxide generation, and decreased superoxide anion release by alveolar macrophages and polymorphonuclear leukocytes. These effects were dose- and time-dependent, the kinetics varying for the different cell types.

Metabolic requirements for maintenance of the chlortetracycline-labeled pool of membrane-bound calcium in human neutrophils

Human neutrophils labeled with chlortetracycline (CTC), commonly used as a probe of membrane-bound calcium, release lysosomal enzymes and exhibit a rapid decrease in fluorescence when exposed to the chemotactic peptide fMet-Leu-Phe or the lectin Con A. This decrease has been attributed to the release of calcium from a membrane-associated "trigger pool." The nature of this putative pool has been further characterized by examining the effects of various inhibitors on the CTC fluorescence response and lysosomal enzyme release from stimulated neutrophils. These agents included inhibitors of glycolysis (2-deoxyglucose and iodoacetate), an uncoupler of oxidative- phosphorylation (KCN), and a sulfhydryl inhibitor (N-ethylmaleimide). Resting neutrophils labelled with CTC demonstrated an enhanced decay of baseline fluorescence when exposed to 2-deoxyglucose or iodoacetate. This suggested that the pool of membrane-bound calcium labelled by this probe was maintained by glycolytic metabolism. Furthermore, 2-deoxyglucose and iodoacetate inhibited both the stimulated decrease in CTC fluorescence and lysosomal enzyme release induced by fMet-Leu-Phe and Con A in a time-dependent manner. KCN did not inhibit either response to stimulation, but did retard the recovery of CTC fluorescence observed when fMet-Leu-Phe was used as the stimulus. High concentrations of N-ethylmaleimide (100 microM) completely inhibited both the CTC fluorescence response and lysosomal enzyme release almost immediately; low concentrations of N-ethylmaleimide (30 microM) inhibited lysosomal enzyme release in a time-dependent manner without significantly affecting changes in CTC fluorescence. These results are consistent with the hypothesis that CTC serves as a probe of membrane-bound "trigger" calcium, the release of which is dependent upon intact glycolysis and is a requirement for lysosomal enzyme release.

Evidence for mediation of acetyl glyceryl ether phosphorylcholine stimulation of adenosine 3',5'-(cyclic)monophosphate levels in human polymorphonuclear leukocytes by leukotriene B4

Acetyl glyceryl ether phosphorylcholine induces human neutrophil aggregation. Incubation of neutrophils with either prostaglandin I2, or the cyclic AMP-dependent phosphodiesterase inhibitor, RO 20-1724 before the addition of PAF-acether attenuates subsequent aggregation. Paradoxically, a small elevation in cyclic AMP is observed coincident with the initiation of PAF-acether-stimulated aggregation. The elevation in cyclic AMP in response to PAF-acether is amplified by RO 20-1724, and the magnitude of the response is dependent upon the concentration of PAF-acether. The elevation in cyclic AMP is not due to prostaglandins, because indomethacin actually enhances the elevation in cyclic AMP induced by PAF-acether. The involvement of the neutrophil 5-lipoxygenase, and subsequent leukotriene B4 synthesis, is suggested by the observation that 5-lipoxygenase inhibitors limit both the elevation in cyclic AMP induced by PAF-acether, and the indomethacin enhancement. This indirect evidence is supported by the fact that leukotriene B4 itself elevates neutrophil cyclic AMP levels in intact cells, and stimulates the adenylate cyclase in broken cell preparations. Although the elevation in cyclic AMP induced by either PAF-acether or leukotriene B4 is coincident with the onset of neutrophil aggregation, it is not obligatory for aggregation. The adenylate cyclase inhibitor 2',5'-dideoxyadenosine blocks the PAF-acether-stimulated increase in cyclic AMP, and actually enhances aggregation. It is suggested that the increase in cyclic AMP observed after the addition of PAF-acether is due to concomitant leukotriene B4 synthesis, and is not obligatory for neutrophil aggregation, but is actually part of a feed-back regulatory system through which PAF-acether and leukotriene B4 can limit their own activity in neutrophils.

Control of the production of oxygen intermediates of human polymorphonuclear leukocytes and monocytes by beta-adrenergic receptors

The control by beta-adrenergic receptors of the production of oxygen radicals by zymosan-stimulated human polymorphonuclear leukocytes (PMN) and monocytes (M phi) was studied in vitro by means of chemiluminescence. In addition we asked whether PMN and M phi exhibit differential sensitivity to beta-adrenergic stimulation. For beta-adrenergic stimulation we applied fenoterol ranging from 10(-5) to 10(-9) M x 2.7. We found a dose-dependent suppression of the production of oxygen radicals, the ID50 being approximately 10(-6) M both for PMN and M phi. By assessment of lactic dehydrogenase release a cytotoxic effect of the drug could be ruled out. When incubated together with the beta-adrenergic antagonist propranolol at 10(-6) and 10(-7) M the suppression effect of fenoterol could be reversed in dose-dependency. Preincubation with fenoterol revealed that the inhibitory action on M phi persisted, in contrast, no such suppression could be verified with PMN. Our findings indicate the control of the production of oxygen intermediates of human PMN and M phi by beta-adrenergic stimulation. Furthermore, selective functional modulation of resting PMN and M phi by beta-adrenoceptors is suggested. These effects may be of importance in vivo, in particular since fenoterol was applied in pharmacological doses.

Divergent effects of methylxanthines and adenylate cyclase agonists on monocyte cytotoxicity and cyclic AMP levels

The effects of theophylline, isobutylmethylxanthine (IBMX), prostaglandin E1 (PGE1), and isoproterenol on monocyte antibody-dependent cytotoxicity (ADCC) were compared with their effects on monocyte cyclic adenosine 3':5'-monophosphate (cAMP) levels. Theophylline (2 mmol/l) halved ADCC and gave a 2-fold increase in cAMP levels. At concentrations not elevating cAMP theophylline inhibited ADCC significantly. In comparison, incubation of monocytes with IBMX, PGE1 and isoproterenol ADCC was only modestly inhibited while these agents gave larger increments (3- to 8-fold) in cAMP levels than theophylline did. Low concentrations of IBMX (50 mumol/l) elevated cAMP without affecting monocyte ADCC whereas PGE1 and isoproterenol inhibited ADCC dose-dependently comparable to increases in cAMP. However, in doses giving similar inhibition of ADCC addition of PGE1 resulted in larger cAMP increments than isoproterenol. The effects of IBMX, PGE1 and isoproterenol was dependent on target cell to effector cell ratio and increased during preincubation with the agents. The inhibition of ADCC by the agents was accompanied by a depressed monocyte lysozyme release and depressed activation of hexose monophosphate shunt. However, only theophylline affected monocyte attachment to sensitized target cells. These results argue against the general inverse relationship between cAMP content and inhibition of monocyte ADCC and demonstrate that theophylline independent on increases in cAMP inhibits ADCC probably by abrogation of monocyte binding activity.

The effect of various stimuli and calcium antagonists on the fluorescence response of chlorotetracycline-loaded human neutrophils

Chlorotetracycline has been used in neutrophils and other cells as probe of the state of membrane-bound calcium. We report here that human neutrophils treated with chlorotetracycline response to soluble secretagogues by a prompt decrease in chlorotetracycline fluorescence. This response was observed within 2-5 s, making it one of the most immediate reactions in neutrophils to stimulation, and was obtained with three secretagogues studied: a chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine, a tumor promotor (phorbol myristate acetate) and a lectin (concanavalin A). The responses of neutrophils to the three stimuli differed both quantitatively and qualitatively. The calcium EGTA, did not effect the onset of the decrease in chlorotetracycline fluorescence, suggesting that the probe was measuring changes in intracellular calcium pools. The intracellular calcium antagonists, TMb-8, W-7 and trifluoperazine, did not block, but actually augmented, the fluorescence response. All four of these calcium antagonists blocked the recovery of chlorotetracycline fluorescence which was usually observed several minutes after stimulation with N-formyl-methionyl-leucyl-phenylalanine. This suggests that recovery was dependent upon both extracellular calcium and active calmodulin. The results are consistent with the hypothesis that changes in chlorotetracycline fluorescence reflect changes in a pool of membrane-bound 'trigger calcium', the release of which is an essential first step in stimulus-response coupling in human neutrophils.

The biologic significance of neutrophil regulatory mechanisms

Self-regulation of feedback control are essential features of most complex biological systems. Neutrophil leukocytes possess potent oxidative and lysomal products for the killing of invading microbes. These toxic products are also capable of causing auto-oxidative injury and tissue damage. Indeed, neutrophils have been implicated as mediators of tissue injury in a number of autoimmune and inflammatory disorders. It is proposed that a sophisticated and complex regulatory mechanism for neutrophil function is operative in healthy individuals. Much of the evidence for this is tentative and fragmentary, but a logical framework is beginning to emerge.

Enhanced monocyte and neutrophil cytotoxicity and normal cyclic nucleotide levels in severe psoriasis

Eighteen patients with active psoriasis were investigated for antibody-dependent cell-mediated cytotoxicity (ADCC) mediated by monocytes and neutrophil leukocytes. Patients with extensive psoriatic lesions showed increased ADCC whereas patients with minimal psoriasis had normal monocyte and neutrophil function. After clinical remission the ADCC became normal. No stimulatory factors in psoriatic serum could be demonstrated. The increased monocyte and neutrophil cytotoxicity in severe psoriasis is not explained by altered cyclic nucleotide levels as cAMP and cGMP levels were normal in psoriatic monocytes and neutrophils showing both increased and normal ADCC. Our results indicate that increased ADCC is secondary to the psoriatic activity.

Activation of the glycogenolytic cascade in human polymorphonuclear leucocytes by different phagocytic stimuli

Human polymorphonuclear leucocytes were found to respond to activation by immunoglobulin opsonized latex particles and to complement opsonized zymosan particles with a rapid transient increase in cAMP concentration, dissociation of the cAMP dependent protein kinase, activation of glycogen phosphorylase and glycogen break down. However, since phosphorylase kinase was not activated, the activation of phosphorylase is believed to be secondary to non-covalent activation of phosphorylase kinase by Ca2+. Activation by the soluble stimulator phorbol myristate acetate resulted in activation of phosphorylase and glycogen break down, whereas no changes in cAMP concentration, protein kinase activity, or phosphorylase kinase activity were observed. The activation of phosphorylase is ascribed to an increase in cytosolic Ca2+ concentration. The response to stimulation by zymosan was strongly inhibited by ethylene glycol-bis-(beta-aminoethyl ether)-N,N1-tetraacetic acid, which did not affect stimulation by either latex particles or phorbol myristate acetate. The same differential effect of ethylene glycol-bis(beta-aminoethyl ether)-N,N1-tetraacetic acid was observed when the response of the cells was measured as increase in oxygen consumption and activation of the hexose monophosphate shunt.

Compartmentalization of cyclic AMP during phagocytosis by human neutrophilic granulocytes

Immunocytochemistry shows that early during phagocytosis of zymosan, adenosine 3',5'-monophosphate (cyclic AMP) appears on the cell surface before the phagosome is internalized. The appearance of cyclic AMP on the cell surface is coincident with that of granule products and regulatory subunit of type I cyclic AMP-dependent protein kinase. Guanosine 3',5'-monophosphate is not associated with the initiation site of phagocytosis, but is observed throughout the granular cytoplasmic region. This sharply localized accumulation of cyclic AMP may serve as a signal for the initiation of phagocytosis.

Stimuli which provoke secretion of azurophil enzymes from human neutrophils induce increments in adenosine cyclic 3'-5'-monophosphate

1. Stimuli for human neutrophils were divided into two classes on the basis of their ability to induce degranulation: complete secretagogues provoked release of both azurophil and specific granules, while incomplete secretagogues only induced release of specific granules. 2. Complete secretagogues, which possessed the ability to induce secretion of azurophil granules, also induced transient increments in total cellular cyclic AMP levels: incomplete secretagogues did not. 3. Complete secretagogues, unlike the incomplete variety, also induced further increments of cyclic AMP in prostaglandin E1-pretreated neutrophils. 4. Inhibition of lysosomal enzyme release by prostaglandin E1 was closely correlated with elevated levels of cyclic AMP induced by the prostaglandin alone, than with the much higher transient increment in cyclic AMP produced by stimulation of prostaglandin E1-treated cells. 5. Our results describe the first biochemical difference between neutrophil responses associated with secretion of azurophil granules, as opposed to specific granules: transient increments in cyclic AMP.

Antibody-dependent monocyte-mediated cytotoxicity in atopic dermatitis. Relation to clinical state and cyclic AMP response

Antibody-dependent monocyte-mediated cytotoxicity was investigated in adult patients with atopic dermatitis. In patients with active dermatitis monocyte cytotoxicity was reduced. Serial studies of individual patients demonstrated that a reduced cytotoxicity in clinical exacerbation did not normalize during clinical remission. The reduced monocyte cytotoxicity was not caused by an abnormal influence of lymphocytes. During the cytotoxicity reaction a rapid and transient elevation of monocyte cyclic AMP occurred. In atopic dermatitis this elevation was decreased, but no relation was found between the monocyte cytotoxicity and the cyclic AMP response in these patients.

Impaired monocyte cyclic AMP responses and monocyte cytotoxicity in atopic dermatitis

Purified monocytes from 21 patients with mild and severe atopic dermatitis (AD) were compared with 22 healthy controls with respect to antibody-dependent cell-mediated cytotoxicity (ADCC) and cyclic adenosine 3',5'-monophosphate (cAMP) responses to stimulatory agents. ADCC was depressed in both severe and mild atopic dermatitis. The patients showed decreased cAMP responses to isoproterenol and histamine, the decrement being more distinct in severe atopic dermatitis. Formation of cAMP was diminished with PGE1 only in patients with severe AD. ADCC is inhibited by the agents that increase cAMP. In the severe dermatitis group reduced inhibition induced by isoproterenol, histamine, but not PGE1, was obtained. It is suggested that a general suppression of membrane activation may explain the reduced cAMP responses to various stimulatory agents and the impaired monocyte cytotoxicity.

Chemotaxin-induced changes in cyclic adenosine monophosphate levels in human neutrophils

Incubation of the chemotactic agent N-formyl-methionyl-leucyl-phenylalanine with human neutrophils produced a rapid elevation of the intracellular level of cyclic adenosine monophosphate (cAMP). This cAMP spike occurred within 30 s after exposure and returned to normal by 5 min.

Increased levels of cyclic adenosine-3',5'-monophosphate in human polymorphonuclear leukocytes after surface stimulation

Levels of cyclic AMP (cAMP) (but not cyclic GMP) in suspensions of human polymorphonuclear leukocytes (PMN) increased promptly after exposure of the cells to stimuli such as the chemotactic peptide N-formyl methionyl leucyl phenylalanine, the immune complex bovine serum albumin/anti-bovine serum albumin and calcium ionophore A23187. cAMP increased rapidly, reaching a maximum of twice the basal level 10--45 s after stimulation; after 2--5 min the amount of cAMP had subsided to basal levels. Elevations in cAMP levels were concurrent with, or followed, membrane hyperpolarization (measured by uptake of the lipophilic cation triphenylmethyl phosphonium) and always preceded lysosomal enzyme release and superoxide anion (O2) production. Elevated cAMP levels could be uncoupled from these later events by removal of extracellular divalent cations, replacement of extracellular Na+ with K+ or choline+, and by use of low concentrations of stimulus; each of these conditions virtually abolished lysosomal enzyme release and O2 generation, while leaving the stimulated elevation of cAMP levels unimpaired. Calcium ionophore A23187 did not provoke membrane hyperpolarization, thus uncoupling changes in membrane potential from changes in cAMP levels. These data suggested that cAMP is not a critical component in the earliest steps of stimulus-secretion coupling. Surface stimulation of cells pretreated with prostaglandins E1 or I2 yielded very high levels of cAMP; these high levels may be an important part of the mechanism by which stable prostaglandins inhibit lysosomal enzyme release and O2 generation.

Phosphorylase kinase from human polymorphonuclear leukocytes

Phosphorylase kinase from human polymorphonuclear leukocytes was investigated in a gel filtered crude preparation (17,000 x g supernatant). It was found to exist in two forms, one (the phosphorylated form) more active than the other (the dephosphorylated form). Interconversion between the two forms was carried out by a cyclic AMP dependent protein kinase and phosphoprotein phosphatase, respectively. The ratio of activity measured at pH 8.0 and 6.0 was 0.36 for the non-activated and 0.83 for the activated form, which is in contrast to the behaviour of phosphorylase kinase from muscle. Km app for the substrate phosphorylase b was 650 U/ml and 85 U/ml for the non-activated and activated form, respectively, whereas Km app for ATP was 0.03 mM and identical for the two forms. The non-activated form of phosphorylase kinase was activated by Ca2+ in the range 10(-7)--5 . 10(-6) M, which may have physiological importance, whereas the activated form was insensitive to variations in Ca2+ concentration between 10(-9) and 10(-3) M.

Effects of catecholamines and glucagon on glycogen metabolism in human polymorphonuclear leukocytes

Addition of 10 micron of the alpha-adrenergic agonist phenylephrine to polymorphonuclear leukocytes suspended in glucose-free Krebs-Ringer bicarbonate buffer (pH 6.7) activated phosphorylase, inactivated glycogen synthase R maximally within 30 s, and resulted in glycogen breakdown. Phenylephrine increased 45Ca efflux relative to control of 45Ca prelabelled cells, but did not affect cyclic adenosine 3',5'-monophosphate (cAMP) concentration. The effects of phenylephrine were blocked by 20 micron phentolamine and were absent in cells incubated at pH 7.4. The same unexplained dependency of extracellular pH was observed with 2.5 nM--2.5 micron glucagon, which activated phosphorylase and inactivated synthase-R, but in addition caused a 30-s burst in cAMP formation. 25 nM glucagon also increased 45Ca efflux. The activation of phosphorylase by phenylephrine and possibly also by glucagon are thought mediated by an increased concentration of cytosolic Ca2+ activating phosphorylase kinase. The effects of 5 micron isoproterenol or 5 micron epinephrine were independent of extracellular pH 6.7 and 7.4 and resulted in a sustained increase in cAMP, an activation of phosphorylase and inactivation of synthase-R within 15 s, and in glycogenolysis. The effects of both compounds were blocked by 10 micron propranolol, whereas 10 micron phentolamine had no effect on the epinephrine action. The efflux of 45Ca was not affected by either isoproterenol or epinephrine. The beta-adrenergic activation of phosphorylase is consistent with the assumption of a covalent modification of phosphorylase kinase by the cAMP dependent protein kinase. Phosphorylation of synthase-R to synthase-D can thus occur independently of increase in cAMP, but the evidence is inconclusive with respect to the cAMP dependent protein kinase also being active in this phosphorylation.