TMB-8 inhibits secretion evoked by phorbol ester at basal cytoplasmic free calcium in quin2-loaded platelets much more effectively than it inhibits thrombin-induced calcium mobilisation

Human Neutrophil Elastase Induce Interleukin-10 Expression in Peripheral Blood Mononuclear Cells through Protein Kinase C Theta/Delta and Phospholipase Pathways

Objective

Neutrophils have an important role in the rapid innate immune response, and the release or active secretion of elastase from neutrophils is linked to various inflammatory responses. Purpose of this study was to determine how the human neutrophil elastase affects the interleukin-10 (IL-10) response in peripheral blood mononuclear cells (PBMC).

Materials and Methods

In this prospective study, changes in IL-10 messenger RNA (mRNA) and protein expression levels in monocytes derived from human PBMCs were investigated after stimulation with human neutrophil elastase (HNE). A set of inhibitors was used for examining the pathways for IL-10 production induced by HNE.

Results

Reverse transcription polymerase chain reaction (RT-PCR) showed that stimulation with HNE upregulated IL-10 mRNA expression by monocytes, while the enzyme-linked immunosorbent assay (ELISA) revealed an increase of IL-10 protein level in the culture medium. A phospholipase C inhibitor (U73122) partially blunt- ed the induction of IL-10 mRNA expression by HNE, while IL-10 mRNA expression was significantly reduced by a protein kinase C (PKC) inhibitor (Rottlerin). A calcium chelator (3,4,5-trimethoxybenzoic acid 8-(diethylamino)octyl ester: TMB-8) inhibited the response of IL-10 mRNA to stimulation by HNE. In addition, pretreatment with a broad-spectrum PKC inhibitor (Ro-318425) partly blocked the response to HNE. Finally, an inhibitor of PKC theta/delta abolished the increased level of IL-10 mRNA expression.

Conclusion

These results indicate that HNE mainly upregulates IL-10 mRNA ex- pression and protein production in moncytes via a novel PKC theta/delta, although partially via the conventional PKC pathway.

Influence of TMB-8 and Thapsigargin on Vasoconstrictor Responses in the Pulmonary Vascular Bed of the Cat

The effects of 8-(diethylamino)octyl-3,4,5-trimethoxybenzoate hydrochloride (TMB-8), a protein kinase C (PKC) inhibitor, and thapsigargin, a CaATPase inhibitor, on pressor responses were studied in the pulmonary vascular bed of the intact-chest anesthetized cat. Under conditions of constant lobar blood flow in the cat, injections of the angiotensin peptides (ANG II), norepinephrine (NE), serotonin (5-HT), Bay K 8644, and the thromboxane A2 mimic U46619 into the lobar arterial perfusion circuit caused dose-related increases in lobar arterial pressure and responses were reproducible with respect to time. Intravenous infusion of TMB-8 at 1.0 mug . kg reduced the pressor response to the ANG II and to NE. However, TMB-8 did not alter pressor responses to 5-HT, U46619, or Bay K 8644. In a separate series of experiments, the effects of thapsigargin were investigated and intravenous infusion of the CaATPase inhibitor at 1.0 mug . kg also reduced pressor responses to the ANG II and to NE but did not alter pressor responses to 5-HT, U46619, and Bay K 8644. The data provide support for the hypothesis that vasoconstrictor responses to ANG II and NE in the pulmonary vascular bed are mediated in part by the activation of protein kinase C (PKC) and sarcoplasmic reticulum CaATPase-sensitive mechanisms in the cat. The present data suggest that pulmonary pressor responses to U46619, 5-HT, and Bay K 8644 are not mediated by PKC or CaATPase activation in the pulmonary vascular bed of the cat.

Nimodipine and TMB-8 potentiate the AMPA-induced lesion in the basal ganglia

Acute injection of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) into the rat globus pallidus leads to calcium precipitation, neuronal death and gliosis. In order to determine whether L-type calcium channels and/or release of Ca(2+) from intracellular stores contribute to the effects of AMPA, nimodipine and 8-(N,N-diethylamino) octyl-3,4,5-trimethoxybenzoate hydrochloride (TMB-8) were administered in combination with AMPA. Nimodipine, but not TMB-8, tended to exacerbate the calcification process initiated by AMPA; the AMPA/nimodipine/TMB-8 combination produced much more calcium deposition than AMPA (+62%, P<0.05). AMPA alone induced a slight but not significant astroglial reaction. Nimodipine slightly enhanced the astroglial reaction triggered by AMPA, whereas TMB-8 doubled it (P<0.001 versus AMPA). These data suggest that blockade of L-type calcium channels by nimodipine enhances calcium imbalance triggered by AMPA, and the calcium release from the endoplasmic reticulum does not participate in the AMPA-induced calcification.

Involvement of calcium/calmodulin signaling in cercosporin toxin biosynthesis by Cercospora nicotianae

Cercosporin is a non-host-selective, perylenequinone toxin produced by many phytopathogenic Cercospora species. The involvement of Ca(2+)/calmodulin (CaM) signaling in cercosporin biosynthesis was investigated by using pharmacological inhibitors. The results suggest that maintaining endogenous Ca(2+) homeostasis is required for cercosporin biosynthesis in Cercospora nicotianae. The addition of excess Ca(2+) to the medium slightly increased fungal growth but resulted in a reduction in cercosporin production. The addition of Ca(2+) chelators [EGTA and 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid] also reduced cercosporin production. Ca(2+) channel blockers exhibited a strong inhibition of cercosporin production only at higher concentrations (>2 mM). Cercosporin production was reduced greatly by Ca(2+) ionophores (A23187 and ionomycin) and internal Ca(2+) blocker [3,4,5-trimethoxybenzoic acid 8-(diethylamino)octyl ester]. Phospholipase C inhibitors (lithium, U73122, and neomycin) led to a concentration-dependent inhibition of cercosporin biosynthesis. Furthermore, the addition of CaM inhibitors (compound 48/80, trifluoperazine, W-7, and chlorpromazine) also markedly reduced cercosporin production. In contrast to W-7, W-5, with less specificity for CaM, led to only minor inhibition of cercosporin production. The inhibitory effects of Ca(2+)/CaM inhibitors were partially or completely reversed by the addition of external Ca(2+). As assessed with Fluo-3/AM (a fluorescent Ca(2+) indicator), the Ca(2+) content in the cytoplasm decreased significantly when fungal cultures were grown in a medium containing Ca(2+)/CaM antagonists, confirming the specificity of those Ca(2+)/CaM antagonists in C. nicotianae. Taken together, the results suggest that Ca(2+)/CaM signal transduction may play a pivotal role in cercosporin biosynthesis in C. nicotianae.

Calcium/Calmodulin-Dependent Signaling for Prepenetration Development in Colletotrichum gloeosporioides

ABSTRACT Colletotrichum gloeosporioides forms a specialized infection structure, an appressorium, for host infection. Contacting hard surface induces appressorium formation in C. gloeosporioides, whereas hydrophobicity of the contact surface does not affect this infection-related differentiation. To determine if the calcium/calmodulin-dependent signaling system is involved in prepenetration morphogenesis in C. gloeosporioides pathogenic on red pepper, effects of calcium chelator (EGTA), phospholipase C inhibitor (neomycin), intracellular calcium modulators (TMB-8 and methoxy verampamil), and calmodulin antagonists (chloroproma-zine, phenoxy benzamine, and W-7) were tested on conidial germination and appressorium formation. Exogenous addition of Ca(2+), regardless of concentration, augmented conidial germination, while appressorial differentiation decreased at higher concentrations. Inhibition of appressorium formation by EGTA was partly restored by the addition of calcium ionophore A23187 or CaCl(2). Calcium channel blockers and calmodulin antagonists specifically reduced appressorium formation at micromolar levels. These results suggest that biochemical processes controlled by the calcium/calmodulin signaling system are involved in the induction of prepenetration morphogenesis in C. gloeosporioides pathogenic on red pepper.

Both IgM and IgG anti-VSG antibodies initiate a cycle of aggregation-disaggregation of bloodstream forms of Trypanosoma brucei without damage to the parasite

Bloodstream forms of Trypanosoma brucei, when aggregated in the presence of either acute immune plasma, acute immune serum, purified IgM anti-VSG antibodies or purified IgG anti-VSG antibodies, subsequently disaggregated with a t1/2 for disaggregation of 15 min at 37 degrees C as long as the trypanosomes were metabolically active at the beginning of the experiment and maintained during the experiment in a suitable supporting medium. The t1/2 for disaggregation was found to be directly dependent upon temperature and inversely proportional to the antibody concentration. The trypanosomes were always motile and metabolically active during aggregation and after disaggregation and were fully infective for a mammalian host following disaggregation as well as able to grow and divide normally during axenic culture. The disaggregation was strictly energy dependent and was inhibited when intracellular ATP levels were reduced by salicylhydroxamic acid or following addition of oligomycin while respiring glucose. In addition the process of disaggregation was dependent upon normal endosomal activity as evidenced by its sensitivity to a wide variety of inhibitors of various endosomal functions. Disaggregation was not due to separation of immunoglobulin chains by either disulphide reduction or disulphide exchange reactions and gross proteolytic cleavage of the immunoglobulins attached to the surface of the parasite was not detected. In addition, gross cleavage or release of the VSG from the surface of the cell did not occur during disaggregation but proteolytic cleavage of a small proportion of either the VSG or the immunoglobulins could not be eliminated from consideration. Finally the mechanism of disaggregation was found to be a regulated process, independent of Ca2+ movements but dependent upon the activity of protein kinase C or related kinases and inhibited by the activity of protein kinase A as evidenced by the effects of a panel of inhibitors and cAMP analogues on the process of disaggregation. The mechanism of disaggregation displayed by trypanosomes aggregated by anti-VSG antibody is proposed to form part of the parasite's defence against the host immune system and functions to aid survival of trypanosomes in the presence of antibody in the host prior to the occurrence of a VSG switching event.

Kinetics of Ca2+ release by InsP3 in pig single aortic endothelial cells: evidence for an inhibitory role of cytosolic Ca2+ in regulating hormonally evoked Ca2+ spikes

1. The role of the InsP3 receptor and its interaction with Ca2+ in shaping endothelial Ca2+ spikes was investigated by comparing InsP3-evoked intracellular Ca2+ release with hormonally evoked Ca2+ spikes in single endothelial cells. 2. InsP3 was generated by flash photolysis of intracellular caged InsP3. InsP3 at 0.2 microM or higher released Ca2+ from stores with a time course comprising a well-defined delay, a fast rise of free [Ca2+] to a peak where net flux into the cystosol is zero, and a slow decline to preflash levels. InsP3-evoked Ca2+ flux into unit cytosolic volume was measured as the rate of change of free [Ca2+]i during the fast rise, d[Ca2+]i/dt (mol s-1 l-1). 3. The mean delay decreased from 433 ms at 0.2 microM to 30 ms at 5 microM. At very high InsP3 concentrations, 78 microM, the delay was shorter, < 10 ms. At low InsP3 concentration the delay was reduced by approximately 30% by prior elevation of free [Ca2+]i, supporting a co-operative action of free [Ca2+] and InsP3 in activation. 4. Both Ca2+ flux and peak free [Ca2+]i increased with InsP3 concentration within each cell. Maximal activation was at > 5 microM, 50% maximum Ca2+ flux was at 1.6 microM InsP3 and the Hill coefficient was between 3.6 and 4.3. A large variation of Ca2+ flux and peak [Ca2+]i was found from cell to cell at the same InsP3 concentration. 5. Strong inhibition of InsP3-evoked flux was produced by an immediately preceding response, with complete inhibition at peak free [Ca2+]i due to the first pulse. InsP3 sensitivity returned over 1-2 min, with 50% recovery at approximately 25 s. The recovery of InsP3 sensitivity may determine the minimum interval between hormonally evoked spikes. 6. Ca2+ flux due to a pulse of InsP3 terminated rapidly, in the continued presence of InsP3, producing a well-defined peak [Ca2+]. A reciprocal relation was found between the duration and the rate of Ca2+ flux, such that high Ca2+ flux was of brief duration. The rate of termination of flux measured as the reciprocal of the 10-90% rise time of free [Ca2+]i showed a linear correlation with Ca2+ flux over a large range in all cells. A systematic deviation from linearity at low InsP3 concentration showed a greater rate of termination at low InsP3 concentration than at high for the same flux. 7. Elevating cytosolic free [Ca2+] by 0.1-2.5 microM strongly inhibited Ca2+ release by InsP3, and buffering free [Ca2+] to low levels greatly prolonged Ca2+ release. Both results support the idea that Ca2+ flux quickly produces locally high free [Ca2+] which inhibits the receptor and terminates Ca2+ release. 8. Hormonally evoked Ca2+ spikes showed a similar reciprocal relation between rise time and Ca2+ flux, seen in the initial Ca2+ spike evoked by extracellular ATP in porcine aortic endothelial cells and by acetylcholine in rat aortic endothelial cells in situ, supporting the idea that the same mechanism of cytosolic Ca2+ inhibition determines the duration of hormonally and InsP3-evoked Ca2+ spikes.

Protection against methoxyacetic-acid-induced spermatocyte apoptosis with calcium channel blockers in cultured rat seminiferous tubules: possible mechanisms

A calcium-mediated mechanism underlying spermatocyte apoptosis induced by 2-methoxyethanol (2-ME) has been previously proposed. This hypothesis was tested in vitro in the present study using cultured juvenile (25 days old) and adult rat seminiferous tubules (JRST and ARST, respectively) with methoxyacetic acid (MAA, the active metabolite of 2-ME). In JRST, spermatocyte degeneration was morphologically obvious 19 hr after a 5-hr exposure to 5 mM MAA. The lesion was unaffected by the presence or absence of extratubular Ca2+. However, MAA-induced cell death was significantly prevented by cotreatment with the dihydropyridines (DHP) nifedipine (50 microM) and nicardipine (20 microM), as well as verapamil (50 microM) and TMB-8 (50 microM), all of which are able to inhibit calcium movement through plasma membranes. However, neither ryanodine, dantrolene, nor cyclosporin A and ruthenium red, which inhibit Ca2+ mobilization from intracellular stores (endoplasmic reticulum and mitochondria), affected the MAA-induced cell death. Inhibition of calcium mobilization through IP3-sensitive pathways by blocking the product of IP3 with manoalide, neomycin, and U73122 did not block the MAA-induced lesion. The protective effects of 50 microM nifedipine and 50 microM TMB-8 were also observed in ARSTs treated with 10 mM MAA for 5 hr. However, when rat testicular sections were immunohistochemically stained with monoclonal antibodies specific for the alpha 1 (the DHP receptor) or the alpha 2 subunits of DHP-sensitive calcium channels, no positive staining was found. Finally, in an attempt to see whether the intracellular free calcium concentrations ([Ca2+]i) in germ cells were increased after the MAA treatment, intact seminiferous tubules were loaded with indo-1 and were measured using laser-scanning confocal microscopy. No detectable increase in the signal in MA A-sensitive spermatocytes was observed, while a 34-54% increase in the signal could be detected in the same cell types when tubules were exposed to 10 microM of the calcium ionophore 4-bromo-A23187 for 5 min. Collectively, these data suggest that the protective effect of calcium channel blockers against the MAA-induced spermatocyte apoptosis is probably not through their blocking effect on DHP-sensitive calcium channels. We postulate alternate mechanisms based on stabilization of cells membranes, or interactions with calmodulin or protein kinase C.

8-(N,N-diethylamino)octyl 3,4,5-trimethoxybenzoate (TMB-8) acts as a muscarinic receptor antagonist in the epithelial cell line HT29

8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate (TMB-8) is a widely used pharmacological tool to investigate the involvement of intracellular Ca2+ stores in cellular responses. In this study we investigate the effect of TMB-8 as a putative inhibitor of "Ca2+ signalling" in single fura-2 loaded HT29 colonic epithelial cells stimulated by ATP, carbachol (CCH) and neurotensin (NT). TMB-8 effectively inhibited the CCH-induced (100 mumol/l intracellular Ca2+ ([Ca2+]i) transient with an IC50 of 20 mumol/l. However, [Ca2+]i transients induced by other phospholipase C coupled agonists ATP (10 mumol/l, n = 4) and NT (10 nmol/l, n = 4) remained unaffected by TMB-8 (50 mumol/l). The agonist-induced [Ca2+]i transients remained equally unaffected by 100 mumol/l TMB-8 when the stimulatory concentration was reduced to 0.5 mumol/l for ATP (n = 4) or 1 nmol/l for NT (n = 4). The competitive nature of the TMB-8-induced inhibition of the CCH-induced [Ca2+]i transient was demonstrated by examining the agonist at various concentrations in absence and presence of the antagonist. High TMB-8 concentrations (100 mumol/l) alone induced a small [Ca2+]i increase (delta[Ca2+]i: 40 +/- 5 nmol/l, n = 7). We assume that this increase is a consequence of a TMB-8 induced intracellular alkalinization (delta pH: 0.1 +/- 0.02, n = 7) occurring simultaneously with the increase in [Ca2+]i. From these results we draw the following conclusions: (1) In sharp contrast to a large number of other studies, but in agreement with studies in other types of cells, these results substantially challenge the value of the "tool" TMB-8 as an "intracellular Ca2+ antagonist"; (2) TMB-8 acts a muscarinic receptor antagonist at the M3 receptor; (3) TMB-8 does not influence the release of Ca2+ from intracellular stores when IP3 signal transduction is activated by ATP or NT; (4) TMB-8 as a weak organic base alkalinizes the cytosol at high concentrations; and (5) TMB-8 induces small [Ca2+]i transients at higher concentrations.

Effects of Calcium and Calmodulin on Spore Germination and Appressorium Development in Colletotrichum trifolii

Spore germination and appressorium formation are important steps in the process of fungal development and pathogenesis. These prepenetration events, which begin with spore attachment and culminate with appressorium maturation, a common scheme for many pathogenic fungi, are prerequisites for penetration of host external barriers and subsequent colonization. Conditions for in vitro spore germination and appressorium development in Colletotrichum trifolii are described. In addition, effects of Ca(sup2+) and calmodulin on these processes have been examined. Results indicate that, as for other pathogenic fungi, appressorium development is induced on a hard surface. The data suggest that disturbance of calcium homeostasis, by ethylene-bis(oxy-ethylenenitrolo)tetraacetic acid (EGTA) or calcium channel blockers, impairs appressorium development. Moreover, calmodulin inhibitors affect both germination and differentiation, implying that the Ca(sup2+)/calmodulin signal transduction pathway is important in the early development of C. trifolii on the plant host surface.

Molecular signals during the early stages of alfalfa anthracnose

Colletotrichum trifolii causes anthracnose disease of alfalfa (Medicago sativa). Fungal perception and response to host signals are likely to be crucial in determining whether successful infection occurs. Our research is based on two premises: (i) that early recognition events result in specific responses and these responses determine whether disease occurs and (ii) recognition involves signal exchange between host and pathogen. We have taken two approaches to study this interaction. One is to isolate "important" genes by methods that make no assumption about their products and then to use molecular characterization (e.g., sequence, expression pattern) to identify the biochemical processes involved. Alternatively, known biochemical entities (genes) that function in signal transduction in other organisms are used as heterologous probes or primers. These molecules are then manipulated to determine functional relevance to the host–pathogen. Data is presented from the later approach and we show that calmodulin, protein kinase C, and a novel protein kinase are specifically expressed during the early stages of infection. Key words: protein kinase, calmodulin, fungal infection, host–parasite interaction, fungal gene expression.

Calcium antagonist, TMB-8, prevents the induction of adaptive response by hydrogen peroxide or X-rays in human lymphocytes

Treatment of human lymphocytes with hydrogen peroxide (10 microM, 30 min, 37 degrees C in PBS) or with 1 cGy X-rays evoked about a 30% decrease in the frequency of micronuclei upon subsequent X-irradiation (1.5 Gy). In addition to a lower micronuclei frequency, we also found an increase in the sedimentation distance of the nucleoids, when measured 90 min (duration of the isolation procedure carried out at 4 degrees C) after the adaptive dose (hydrogen peroxide or X-rays) and preceding the challenge dose. To test whether Ca2+ is involved in the induction of the adaptive response pathway, we treated cells with the calcium chelator, EGTA. When EGTA was given at the same time as the adaptive dose, it prevented the development of the adaptive response. In addition, the calcium antagonist, TMB-8, also prevented the development of the adaptive response as it prevented the reduction of both micronuclei and increased nucleoid sedimentation. Cellular treatment with TMB-8 increased the free [Ca2+] by 40%, when given together with hydrogen peroxide. The faster sedimenting nucleoids from adapted cells were also examined by ethidium bromide titration; there was no indication of any change in supercoil density or loop size. Psi-tectorigenin, an inhibitor of phosphatidylinositol turnover, did not modify the adaptive response, indicating that inositol (1,4,5)-trisphosphate is not involved in the induction of the adaptive response, but free Ca2+ ions are.

Calcium-independent effects of TMB-8. Modification of phospholipid metabolism in neuroblastoma cells by inhibition of choline uptake

TMB-8 [8-(NN-diethylamino)-octyl-3,4,5-trimethoxybenzoate] blocks agonist-stimulated release of Ca2+ from intracellular sites in many cell lines and is often used to distinguish between dependence on extracellular and intracellular Ca2+. In N1E-115 neuroblastoma cells, TMB-8 did not alter the resting cytosolic Ca2+ concentration in unstimulated cells, yet phospholipid metabolism was greatly affected. At concentrations of TMB-8 (25-150 microM) that inhibit Ca2+ release, phosphatidylcholine formation was inhibited, whereas synthesis of phosphatidylinositol, phosphatidylglycerol and phosphatidylserine was stimulated. Unlike other cationic amphipathic compounds, TMB-8 did not inhibit phosphatidate phosphatase or enzymes in the pathway from choline to phosphatidylcholine. Choline transport was the major site of action. TMB-8 was a competitive inhibitor (Ki = 10 microM) of low-affinity (Kt = 20 microM) choline transport. When added at the same time as labelled precursor, TMB-8 also decreased cellular uptake of phosphate and inositol, but not that of ethanolamine or serine. In prelabelled cells, continued uptake and incorporation of phosphate and inositol were not affected. Under these conditions phosphatidylinositol synthesis was increased 2-fold and, like the effect on phosphatidylcholine, reached a plateau at 100 microM-TMB-8. Phosphatidylglycerol synthesis increased linearly with TMB-8 concentration to 40-fold stimulation at 150 microM, suggesting a selective effect on synthesis of phosphatidylglycerol from CDP-diacylglycerol. Phosphatidylserine synthesis was also increased up to 3-fold. These Ca(2+)-independent effects limit the use of TMB-8 in studies of cell signalling that involve stimulated phosphatidylinositol and phosphatidylcholine metabolism.

Effects of 8-(N,N-diethylamino)octyl 3,4,5-trimethoxybenzoate (TMB8) on rat atrial muscle

Rat atria loaded in vitro with the dye INDO-1 produced fluorescence signals indicative of changes in cytoplasmic calcium ion concentration ([Ca2+]c). Such atria showed systolic/diastolic fluctuations in fluorescence indicative of a systolic rise and a diastolic fall in [Ca2+] while being superfused with a solution containing a normal Ca2+ concentration. Some atria were then exposed to a low [Ca2+] in the superfusate. This caused negative inotropism and fluorescence changes indicative of a decline in [Ca2+]c. Both of these responses were reversed by adding 8-(N,N-diethylamino)octyl 3,4,5-trimethoxybenzoate (TMB8; 2 microM) to the superfusate. Some atria were exposed instead either to a low [K+] in the superfusate or to an ouabain-containing superfusate. These atria developed a contracture, associated with fluorescence changes indicative of a rise in [Ca2+]c. The addition of TMB8 (2 microM) now relaxed the contracture, and this was associated with fluorescence changes indicative of a decline in [Ca2+]c. Atria that were exposed for 15 min to a low [Na+] in the superfusate developed a period of positive inotropism, followed by a brief period of negative inotropism on return to the normal superfusate. The period of positive inotropism was associated with fluorescence changes indicative of a rise in [Ca2+]c and the period of negative inotropism with a decline in [Ca2+]c to below baseline levels. All of these responses were less marked in atria exposed throughout to superfusates containing TMB8 (2 microM). Some atria were loaded with the dye SNARF-1. This emits fluorescence signals indicative of changes in cytoplasmic pH (pHc). These atria showed no systolic/diastolic fluctuation of fluorescence, but when superfused with a bicarbonate-free solution they displayed a change in fluorescence indicative of a decline in pHc in response to the addition of either ouabain or TMB8. Similarities were found between the effects produced by TMB8 and those produced by amiloride or dichlorobenzyl amiloride, suggesting that all three agents inhibit plasmalemmal Na+/Ca2+ and Na+/H+ exchange.

Evidence for receptor-mediated calcium entry and refilling of intracellular calcium stores in FRTL-5 rat thyroid cells

The aim of the present study was to investigate the relationship between agonist-induced changes in intracellular free Ca2+ ([Ca2+]i) and the refilling of intracellular Ca2+ stores in Fura 2-loaded thyroid FRTL-5 cells. Stimulating the cells with ATP induced a dose-dependent increase in ([Ca2+]i). The ATP-induced increase in [Ca2+]i was dependent on both release of sequestered intracellular Ca2+ as well as influx of extracellular Ca2+. Addition of Ni2+ prior to ATP blunted the component of the ATP-induced increase in [Ca2+]i dependent on influx of Ca2+. In cells stimulated with ATP in a Ca(2+)-free buffer, readdition of Ca2+ induced a rapid increase in [Ca2+]i; this increase was inhibited by Ni2+. In addition, the ATP-induced influx of 45Ca2+ was blocked by Ni2+. Stimulating the cells with noradrenaline (NA) also induced release of sequestered Ca2+ and an influx of extracellular Ca2+. When cells were stimulated first with NA, a subsequent addition of ATP induced a blunted increase in [Ca2+]i. If the action of NA was terminated by addition of prazosin, and ATP was then added, the increase in [Ca2+]i was restored to control levels. Addition of Ni2+ prior to prazosin inhibited the restoration of the ATP response. In the presence of extracellular Mn2+, ATP stimulated quenching of Fura 2 fluorescence. The quenching was probably due to influx of Mn2+, as it was blocked by Ni2+. The results thus suggested that stimulating release of sequestered Ca2+ in FRTL-5 cells was followed by influx of extracellular Ca2+ and rapid refilling of intracellular Ca2+ stores.

An increase of intracellular free Ca2+ is essential for spontaneous meiotic resumption by mouse oocytes

The involvement of calcium ions in the mechanism of meiotic resumption has been studied in mouse oocytes made resistant to the lethal effects of calcium-free medium (CFM) by zona pellucida removal (De Felici et al., '89). We show here that such oocytes undergo meiotic resumption in CFM (as evaluated by germinal vesicle breakdown, GVBD) at a rate comparable to that shown by oocytes cultured in medium containing 1.7 mM Ca2+. The addition to CFM of 50 u M Quin2/AM (a membrane permeable, high affinity Ca2+ chelator) totally prevents GVBD, while purported antagonists of Ca2+ release from intracellular stores, such as 150 uM 8-(N,N-diethylamino)octyl-3-4-5 trimethoxybenzoate (TMB-8) or 300 uM chlortetracycline, only cause a slight meiotic delay. On the other hand, if the oocytes are pre-incubated for 30 min in CFM supplemented with 100 uM TBM-8 plus 0.2 mM dibutyryl-cyclic AMP (dbcAMP, a reversible inhibitor of GVBD), and then cultured in the same medium, without dbcAMP, a sustained inhibition of meiotic maturation is obtained. Our observations suggest that an increase in intracellular free Ca2+ is essential for meiotic resumption by mouse oocytes; in the experimental absence of external Ca2+, release of the cation from internal stores is sufficient to allow meiotic resumption.

Mechanism of chemical carcinogenesis: an alternative hypothesis

Ultimate carcinogens are usually very reactive electrophilic species and therefore of transient existence in the cell. Both because of the biological reactivity and the inherent danger in their reaction with DNA, direct interaction with the latter is prevented, especially in higher mammalian cells, by various cell defence mechanisms and, lastly, by a nuclear membrane monitoring system. Hence, reaction of chemical carcinogen with nuclear DNA is possible only when the cell is overwhelmed leading to cell death, or following a temporary breach of the nuclear membrane control points, but the DNA damage in the latter is totally reparable. Both situations are therefore of no consequence to chemical carcinogenesis. Instead, the excess electrical charge created by the physical presence of the electrophilic carcinogens is hypothesized to predispose the cell to irreversible genetic changes like cellular oncogene activation, or uncontrolled cell proliferation common to cancerous cells. These effects would be catalyzed by a Na+-H+ exchange-mediated intracellular alkalinization resulting from the cell's attempt to restore electrical neutrality by elevating the Na(+)-pump activity, fuelled by an increased Na+/H+ antiport.

Influence of 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate (TMB-8) on cell cycle progression and proliferation of cultured arterial smooth muscle cells

8-(N,N-Diethylamino)octyl-3,4,5-trimethoxybenzoate (TMB-8), a putative inhibitor of intracellular calcium mobilization, causes a dose-dependent inhibition of serum-induced proliferation of arterial smooth muscle cells in culture. Neither early rise in cytosolic calcium concentration nor induction of early induced cell cycle dependent genes (c-fos, ornithine decarboxylase) are inhibited after serum stimulation in presence of 100 microM TMB-8. In contrast, expression of thymidine kinase, a gene normally induced in late-G1 phase, is entirely inhibited by TMB-8. Taken together with flow cytometry studies, these results indicate that TMB-8 blocks cell cycle progression in mid- or late-G1 phase by a mechanism not directly related to early responses to serum stimulation since TMB-8 is also effective when introduced several hours after serum stimulation.

Ligands to the platelet fibrinogen receptor glycoprotein IIb-IIIa do not affect agonist-induced second messengers Ca2+ or cyclic AMP

Previous studies have suggested that the platelet glycoprotein complex GPIIb-IIIa, which is the putative fibrinogen receptor, regulates Ca2+ influx into platelets, possibly operating as a Ca2+ channel. We have used RGD-peptides (peptides containing the sequence Arg-Gly-Asp; disintegrins), isolated from snake venoms, that have a high affinity and specificity for the fibrinogen-binding site of GPIIb-IIIa to address the question of whether blocking this site inhibits Ca2+ movement from the extracellular medium to the cytosol. Using fura-2-loaded human platelets, we found that neither disintegrins nor a monoclonal antibody (M148) to the GPIIb-IIIa complex altered the level of cytosolic Ca2+ obtained when the cells were stimulated with various agonists in the presence of either nominal or 1 mM extracellular Ca2+. In the presence of Mn2+, an ion that quenches fura-2 fluorescence, fura-2-loaded platelets were stimulated with thrombin or ADP. Neither disintegrins nor the monoclonal antibody altered the kinetics or the amount of quenching of fura-2 fluorescence by Mn2+. These data indicate that the binding of ligands to the fibrinogen receptor is not associated with an inhibition of Ca2+ movement through a receptor-operated channel. Furthermore, the disintegrins have no effect on platelet cyclic AMP metabolism in either the presence or the absence of phosphodiesterase inhibitors.

Verapamil inhibits phosphatidic acid formation and modifies phosphoinositide metabolism in stimulated platelets

Rabbit platelet-rich plasma was incubated with [32P]orthophosphate, after which the platelets were washed, further incubated in the absence or presence of verapamil and subsequently stimulated with PAF-acether or thrombin. In the absence of verapamil, a rapid increase in radioactivity in phosphatidic acid was observed in platelets stimulated with PAF-acether or thrombin. This was inhibited by verapamil over the concentration range 10(-7) to 10(-4) M, at which concentration the rise in phosphatidic acid was completely abolished. In unstimulated platelets, 10(-4) M verapamil induced an increase in radioactivity in polyphosphoinositides but not significantly in phosphatidylinositol. When these verapamil-treated platelets were stimulated with PAF-acether or thrombin, there was a rapid, sustained loss of the additional radioactivity induced in the polyphosphoinositides by verapamil. Polyphosphoinositide radioactivity remained unchanged in platelets stimulated in the absence of verapamil. Verapamil may stimulate formation of a separate pool of polyphosphoinositide which is susceptible to agonist-induced phospholipase C, and failure to re-synthesize this polyphosphoinositide could result from inhibition of phosphatidic acid synthesis.

The effects of TMB-8 on the shape changes of vascular endothelial cells resulting from exposure to various inflammatory agents

Pre-treatment of the endothelial cells lining the guinea pig inferior vena cava with 8-(diethylamino)octyl 3,4,5-trimethoxybenzoate (TMB-8) (10 microM) in vitro significantly reduced the shape changes resulting from subsequent exposure to platelet activating factor (PAF) (0.1 microM), calcium ionophore A23187 (10 microM), histamine (300 microM), bradykinin (2 microM), prostaglandin E2 (PGE2) (30 microM), or leukotrienes (LT) C4, D4 or E4 (1 microM). Since TMB-8 is an intracellular calcium antagonist, this provides evidence to support the suggestion that these inflammatory agents increase the concentration of intracellular calcium which brings about a contraction of the actin-myosin complex resulting in endothelial cell shape changes, and the formation of interendothelial cell gaps.

Mechanism of shear-induced prostacyclin production in endothelial cells

Human umbilical vein endothelial cells at confluence were subjected to steady shear flow. It was previously shown that flow induced a burst in prostacyclin production followed by a sustained stimulation of production several fold higher than basal levels (1). In the presence of EGTA, prostacyclin production was inhibited in the steady state phase by 74%. Preincubation of endothelial cells with quin2/AM, used here as an intracellular calcium chelator, also inhibited the production of prostacyclin (83%). Inhibition of intracellular calcium mobilization had no significant effect. Incubation of cells with nifedipine, a voltage operated channel blocker, had no effect on shear induced prostacyclin production, whereas ibuprofen decreased shear induced prostacyclin production. RHC-80267, a diacylglycerol lipase inhibitor, inhibited 66% of shear induced PGI2 production. Our results suggest that both extracellular and intracellular Ca2+ are necessary and the phospholipase C pathway may be the main source for liberating arachidonic acid in shear induced prostacyclin production.

Thrombin-stimulated elevation of human endothelial-cell cytoplasmic free calcium concentration causes prostacyclin production

Endothelial cells are known to release prostacyclin (PGI2) in response to agonists, and this has generally been assumed to be caused, at least in part, by activation of a phospholipase A2 by elevated concentrations of cytoplasmic free calcium ([Ca2+]i). However, it has been shown in the blood platelet that agonists can cause arachidonate release without elevating [Ca2+]i. In the present study, rigorous analysis is made of the [Ca2+]i-dependence of PGI2 production in the human umbilical-vein endothelial cell. Thrombin caused a rapid increase in [Ca2+]i from the resting basal value of 0.1 microM to a peak, within 10-15 s, of approx. 2 microM. In the absence of extracellular Ca2+, [Ca2+]i then declined back to the resting value within 2-3 min. In the presence of extracellular Ca2+, [Ca2+]i partly decreased to a new steady-state value of approx. 1 microM. The elevated [Ca2+]i was maintained while the stimulus and the source of extracellular Ca2+ were present, suggesting that it was dependent on influx of Ca2+ across the plasma membrane. Thrombin stimulated the production of PGI2 in the presence or in the absence of extracellular Ca2+. However, the production of PGI2 was more prolonged in the presence of extracellular Ca2+. Total accumulated amounts of 6-oxo-prostaglandin F1 alpha on stimulation with thrombin without extracellular Ca2+ were only 65% of those accumulated with extracellular Ca2+ present. Cells depleted of extracellular and intracellular sources of Ca2+ by incubation with 1 mM extracellular EGTA and exposing them to ionomycin to discharge intracellular stores produced no elevation of [Ca2+]i on stimulation with thrombin or production of PGI2. The threshold [Ca2+]i required to support the production of PGI2 was measured to be 0.8-1.0 microM by using different doses of ionomycin selectively to increase [Ca2+]i. This relationship between [Ca2+]i and PGI2 production was similar to that produced by using different doses of thrombin. Our results show that the major and probably exclusive intracellular stimulus for the production of PGI2 by the vascular endothelial cell in response to thrombin is the elevation of [Ca2+]i.

Effects of calcium antagonists, calmodulin antagonists, and methylated xanthines on polar lobe formation and cytokinesis in fertilized eggs of Ilyanassa obsoleta

We have studied the ability of fertilized eggs of Ilyanassa obsoleta to undergo polar lobe formation and cytokinesis in the presence of Ca2+ antagonists (Ca2+ channel blockers, Ca2+ uptake inhibitors). Earlier work had suggested little need for exogenous Ca2+ during these cellular shape changes. Again it appears that exogenous Ca2+ probably is not required, based on cell ability to undergo the shape changes with no, or only minor, delay in the presence of 50 mM La3+ at pH 6.5, 10 mM concentrations of Ni2+ or Co2+, 1 mM Cd2+, and 100 microM concentrations of Mn2+, papaverine, verapamil, D600, or diltiazem. In nominally Ca2+-free seawater (containing approximately 10 microM Ca2+) (CFSW), there still is no effect of Cd2+ (up to 100 microM), Ni2+, Co2+, Mn2+, or diltiazem; however, papaverine, verapamil, and D600 in CFSW cause longer delays in the shape changes than they do in the presence of normal levels of Ca2+ (SW). In 10-50 microM nifedipine, shape changes are progressively delayed to the same extent in both SW and CFSW, but more so in CFSW at concentrations above 50 microM nifedipine. Among calmodulin antagonists, trifluoperazine up to 100 microM was without effect, but chlorpromazine at 25-100 microM and calmidazolium at 50-100 microM caused substantial, concentration-dependent delays in the starting times for the shape changes. Methylxanthines caused a substantial speed-up in the starting times for both polar lobe formation and cytokinesis. The most effective of these, caffeine, at optimal concentrations of 0.7-10 mM in SW or CFSW caused shape changes to occur 12-15 min earlier than in controls undergoing a normal 50-min cycle. Caffeine is known to cause release of Ca2+ from muscle sarcoplasmic reticulum. A putative antagonist of intracellular Ca2+ mobilization, TMB-8, significantly inhibited the shape changes of the Ilyanassa cells, whereas a variety of inhibitors of exogenous Ca2+ uptake noted above did not inhibit. We conclude that Ca2+ may be necessary for polar lobe formation and cytokinesis in Ilyanassa cells, but that it may be released from intracellular, sequestered stores rather than derived from exogenous sources.

The role of calcium in stimulation of activated T lymphocytes with interleukin 2

In a study of the role of Ca++ in the stimulation of activated T lymphocytes with interleukin 2 (IL-2) it was found that IL-2-induced proliferation can occur independently of extracellular calcium. Further, there was no correlation between triggering of DNA synthesis and an increase in free cytoplasmic calcium. However, IL-2 induced an increased uptake of 45Ca++ from the extracellular medium. Since there is no increase in free cytoplasmic calcium, it must be assumed that this is caused by an increase in membrane-associated calcium. Further, the calcium channel-blocking agent, verapamil, and TMB-8, a putative inhibitor of mobilization of calcium from intracellular pools, both exerted a dose-dependent inhibition of IL-2-induced DNA synthesis in activated T lymphocytes. We conclude that calcium is not a second messenger in activated T lymphocytes stimulated by IL-2, but our results indicate that calcium may play a role at membrane level.

Age related decline in aluminum-activated human platelet adenylate cyclase: post-receptor changes in cyclic AMP second messenger signal amplification in normal aging and dementia of the Alzheimer type

Low, micromolar concentrations of aluminum (in the presence of NaF) were shown to strongly activate human platelet adenylate cyclase and provided a useful probe for evaluating cyclic AMP second messenger function distal to the receptor: The effect of normal aging and disease state on second messenger activity in man was studied by measurements of the aluminum-activated enzyme. A significant decline in aluminum-stimulated platelet adenylate cyclase activity in older, healthy subjects was observed. An age-associated decline in NaF-stimulated cyclic AMP synthesis was also demonstrated for normal, non-demented subjects. These findings suggest an age-associated lesion at the level of the guanine nucleotide regulatory protein/catalytic subunit of the adenylate cyclase complex. However, for patients with Alzheimer's disease no such decline in platelet adenylate cyclase activity was detected, and increased sensitivity to both aluminum and NaF was demonstrated.

Action of TMB-8 (8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate) on cytoplasmic free calcium in adrenal glomerulosa cell

To clarify the action of 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate (TMB-8) on cellular calcium handling, changes in cytoplasmic free calcium concentration ([Ca2+]c) were studied in adrenal glomerulosa cell with a calcium-sensitive photoprotein, aequorin. Results of our previous study demonstrate that 100 microM TMB-8 almost completely blocks aldosterone response to angiotensin II (Biochem. J. 232 (1985) 87-92). At 50 or 100 microM, TMB-8 decreased basal [Ca2+]c significantly; however, these doses of TMB-8 had little effect on an angiotensin-induced increase in [Ca2+]c. When angiotensin-induced calcium release from an intracellular pool(s) was assessed by measuring changes in [Ca2+]c in the presence of 1 microM extracellular Ca2+, 100 microM TMB-8 had little inhibitory effect on angiotensin-induced calcium release. A higher dose of TMB-8 (250 microM) slightly inhibited calcium release. Additionally, TMB-8 did not affect exogenous arachidonic acid-induced calcium release. In contrast, 50 microM TMB-8 markedly inhibited 8 mM potassium-induced increase in [Ca2+]c. These results indicate that a major action of TMB-8 on cellular calcium is an inhibition of calcium influx but not of calcium release. We suggest that TMB-8 should not be used as an 'inhibitor of calcium release'.

Accumulations of cyclic AMP and inositol phosphates in guinea pig cerebral cortical synaptoneurosomes: enhancement by agents acting at sodium channels

Activation of alpha 1-adrenergic receptors by norepinephrine in guinea pig cortical synaptoneurosomes augments accumulations of cyclic AMP elicited by 2-chloroadenosine and concomitantly increases formation of inositol phosphates. Various agents that affect calcium channels or sites of action of calcium have little or no effect on cyclic AMP accumulation elicited either with 2-chloroadenosine, or with a 2-chloroadenosine/norepinephrine combination, nor did they markedly affect formation of inositol phosphates elicited by norepinephrine. However, EGTA reduces both cyclic AMP accumulation and inositol phosphate formation. Agents such as batrachotoxin, scorpion (Leiurus) venom and pumiliotoxin B that are active at voltage-dependent sodium channels enhance accumulations of cyclic AMP and inositol phosphates. These effects are blocked by tetrodotoxin. It is proposed that enhanced influx of sodium ions increases phosphatidylinositol metabolism, resulting in formation of diacylglycerols and inositol phosphates, and that the former, through activation of protein kinase, causes an enhancement of cyclic AMP accumulations in brain tissue.

Collagen increases cytoplasmic free calcium in human platelets

The role of changes in cytoplasmic free calcium in response to collagen was studied in human platelets loaded with the fluorescent calcium indicator, quin2. In the presence of 1mM external calcium, collagen caused a biphasic increase in cytoplasmic free calcium. In the absence of external calcium, there was a much smaller increase in cytoplasmic free calcium. These findings suggest that collagen increases cytoplasmic free calcium, partly by discharge of internal calcium, but mainly by stimulating calcium influx. Inhibition of cyclooxygenase by aspirin markedly reduced the second phase of the calcium response. Removal of ADP with apyrase resulted in complete inhibition of the second phase of the calcium response. The combination of apyrase and aspirin completely inhibited aggregation and the shape change caused by collagen. The calcium-entry blocking agent, verapamil, also inhibited the second phase of the calcium response to collagen. The increase in cytoplasmic free calcium is fast enough to be involved in the platelet response to collagen and these findings suggest that ADP and metabolites of arachidonic acid mediate the second phase of the calcium response to collagen.

Mechanism of inhibitory action of TMB-8 [8-(NN-diethylamino)octyl-3,4,5-trimethoxybenzoate] on aldosterone secretion in adrenal glomerulosa cells

The mechanism of 8-(NN-diethylamino)octyl-3,4,5-trimethoxybenzoate (TMB-8) action was evaluated in isolated adrenal glomerulosa cells. TMB-8 inhibits both angiotensin II- and K+-stimulated aldosterone secretion in a dose-dependent manner. The ID50 for angiotensin II- and K+-stimulated aldosterone secretion is 46 and 28 microM, respectively. In spite of the fact that 100 microM-TMB-8 inhibits angiotensin II-stimulated aldosterone secretion almost completely, TMB-8 (100 microM) does not inhibit angiotensin II-induced 45Ca2+ efflux from prelabelled cells nor does it affect inositol 1,4,5-trisphosphate-induced calcium release from non-mitochondrial pool(s) in saponin-permeabilized cells. TMB-8 has no inhibitory effect on A23187-induced aldosterone secretion, but 12-O-tetradecanoylphorbol 13-acetate-induced aldosterone secretion is completely abolished. TMB-8 effectively inhibits both angiotensin II- and K+-induced increases in calcium influx but has no effect on A23187-induced calcium influx. TMB-8 inhibits the activity of protein kinase C dose-dependently. These results indicate that TMB-8 inhibits aldosterone secretion without inhibiting mobilization of calcium from an intracellular pool. The inhibitory effect of TMB-8 is due largely to an inhibition of plasma membrane calcium influx, but this drug also inhibits the activity of protein kinase C directly.

Alterations in calcium metabolism in phorbol ester-treated mouse peritoneal macrophages

Phorbol 12-myristate 13-acetate (PMA)-treated macrophages exhibited a two-fold increase in the rate of 45Ca++ efflux and over a three-fold increase in the size of the exchangeable calcium pool, resulting in almost a seven-fold increase in the slow phase of calcium efflux. The calcium antagonist 8-(N,N-diethylamino) octyl 3,4,5-trimethoxybenzoate hydrochloride (TMB-8) by itself did not affect calcium efflux in macrophages; but abolished the PMA-induced increase in the rate of calcium efflux. The divalent cationphore A23187 increased the rate constant of the fast phase of calcium efflux two-fold when applied alone or when applied with PMA. These effects might be linked to ionophore enhancement and TMB-8 inhibition of PMA-induced macrophage chemotaxis and spreading (previously reported in Cell Calcium 3:503-514 and Cancer Research 43:3385-3391). No change in calcium efflux was observed if cells were exposed to PMA only during the efflux experiment suggesting that a prolonged exposure to PMA is required to elicit changes in calcium flux. Increased 45Ca++ remained in treated cells at each time point perhaps reflecting the PMA-induced increase in exchangeable calcium.

Osmotic and phorbol ester-induced activation of Na+/H+ exchange: possible role of protein phosphorylation in lymphocyte volume regulation

The Na+/H+ antiport is stimulated by 12-O-tetradecanoylphorbol-13, acetate (TPA) and other phorbol esters in rat thymic lymphocytes. Mediation by protein kinase C is suggested by three findings: (a) 1-oleoyl-2-acetylglycerol also activated the antiport; (b) trifluoperazine, an inhibitor of protein kinase C, blocked the stimulation of Na+/H+ exchange; and (c) activation of countertransport was accompanied by increased phosphorylation of specific membrane proteins. The Na+/H+ antiport is also activated by osmotic cell shrinking. The time course, extent, and reversibility of the osmotically induced and phorbol ester-induced responses are similar. Moreover, the responses are not additive and they are equally susceptible to inhibition by trifluoperazine, N-ethylmaleimide, and ATP depletion. The extensive analogies between the TPA and osmotically induced effects suggested a common underlying mechanism, possibly activation of a protein kinase. It is conceivable that osmotic shrinkage initiates the following sequence of events: stimulation of protein kinase(s) followed by activation of the Na+/H+ antiport, resulting in cytoplasmic alkalinization. The Na+ taken up through the antiport, together with the HCO3- and Cl- accumulated in the cells as a result of the cytoplasmic alkalinization, would be followed by osmotically obliged water. This series of events could underlie the phenomenon of regulatory volume increase.