Murine cardiotrophin-1 stimulates the acute-phase response in rat hepatocytes and H35 hepatoma cells

Mouse cardiotrophin-1 (CT-1) is a hypertrophy-inducing factor for cardiac myocytes and interacts with cell surface receptors that incorporate the signaling molecule gp130. Because other cytokines utilizing this receptor subunit stimulate acute-phase protein synthesis, we tested cardiotrophin-1 in in vitro assays of protein synthesis by primary rat hepatocytes, rat hepatoma cells (H35), and human hepatoma cells (HepG2). CT-1 showed a dose-dependent induction of protein synthesis by primary rat hepatocytes, with effective concentrations ranging from 0.1 to 100 ng/ml. Production of a number of acute-phase proteins, including alpha 1-cysteine proteinase inhibitor ( alpha 1-CPI), alpha 1-proteinase inhibitor (alpha 1-Pi), alpha 2-macroglobulin, and alpha 1-acid glycoprotein, was markedly increased at 48 and 72 h of cytokine stimulation. In rat H35 cells, CT-1 stimulated alpha 1-Pi and alpha 1-CPI protein production and upregulated alpha 1-CPI mRNA levels with similar potency. Compared with other IL-6-type human cytokines at optimal concentrations in parallel assays, CT-1 induced similar levels of acute-phase proteins as human oncostatin M (OM) and leukemia inhibitory factor (LIF), whereas human IL-6 induced the greatest levels of alpha 1-CPI or alpha 1-Pi production by H35 cells. When tested on human HepG2 cells, murine CT-1 was far less effective, in that it stimulated alpha 1-antichymotrypsin production only at very high concentrations (100 ng/ml) but did not alter haptoglobin or alpha 1-Pi. Human OM and IL-6 were effective at lower concentrations and induced much higher levels of acute-phase protein synthesis, whereas LIF activity was similar to that to CT-1. These results show that murine CT-1 is a strong acute-phase mediator for rat hepatocytes in vitro and its activity is similar to LIF on rat hepatocytes, H35 cells, and HepG2 cells.

Oncostatin M inhibits IL-1-induced expression of IL-8 and granulocyte-macrophage colony-stimulating factor by synovial and lung fibroblasts

The role of oncostatin M (OM) in modulating production of cytokines by connective tissue cells is largely unexplored. We have examined the effects of stimulating fibroblast cultures derived from human synovium and from normal lung with OM alone or in combination with IL-1, IL-1 alpha (or IL-1 beta) at 1 or 5 ng/ml, stimulated production of high levels of granulocyte-macrophage CSF (GM-CSF), IL-8, and IL-6 protein. At various concentrations (0.1-50 ng/ml), OM alone failed to significantly enhance protein or mRNA levels of GM-CSF, IL-8, IL-6, or G-CSF after 18 h of stimulation. When combined with IL-1 alpha or -beta, OM caused a dose-dependent inhibition of the IL-1-induced level of IL-8 and GM-CSF protein and mRNA expression, whereas IL-6 production was simultaneously enhanced. In contrast, when IL-6 or leukemia inhibitory factor (two other cytokines that share gp130 receptor components with OM) were used in a similar fashion in combination with IL-1 alpha, neither cytokine consistently altered the IL-1-induced levels of IL-8, GM-CSF, or IL-6. In addition, only OM and not IL-6 or leukemia inhibitory factor was able to induce STAT-1 nuclear factor binding to DNA in stimulated fibroblast extracts as measured by electrophoretic mobility shift assay. These results suggest that OM can significantly alter cytokine profiles of stimulated fibroblasts and may play a unique role in modulating cytokine production by these cells at sites of inflammation.

Pentobarbitone modulation of NMDA receptors in neurones isolated from the rat olfactory brain

1. The action of pentobarbitone on the N-methyl-D-aspartate (NMDA) receptors of neurones freshly dissociated from the olfactory bulb and olfactory tubercle has been studied using patch-clamp techniques. 2. Pentobarbitone produced a concentration-dependent depression of the currents evoked by NMDA with an IC50 value of c. 250 microM. 3. Analysis of the NMDA-evoked noise produced power spectra that could be fitted by the sum of two Lorentzians with corner frequencies of 17 and 82 Hz. Pentobarbitone increased the corner frequency of the high frequency component but did not alter the apparent single channel conductance estimated from the noise. 4. Single channel recordings in either the cell-attached or outside-out patch configurations revealed that NMDA (20 or 50 microM) opened channels with a main conductance level around 55 pS and a principal subconductance around 44 pS. The uncorrected mean open time of the channels was 3.4 ms and mean burst length was 6.0 ms. Mean cluster length was about 12 ms. 5. Pentobarbitone produced a concentration-dependent reduction in both mean open time and burst length. Mean cluster length was much less affected. Pentobarbitone did not decrease unitary current amplitude or bias the open-state current amplitude distribution in favour of a particular substate. 6. From these data it appears that pentobarbitone depresses the inward current evoked by NMDA by reducing the probability of channel opening and this results from a shortening of the lifetime of the channel open state and by decreasing burst length.

Cytokines oncostatin M and interleukin 1 regulate the expression of the IL-6 receptor (gp80, gp130)

The steady-state mRNA levels of the interleukin 6 receptor (IL-6R, gp80) and its signal transducing molecule, gp130, were examined in the rat hepatoma cell line, H-35, stimulated by cytokines IL-6, IL-1, oncostatin M (OSM) and/or Dexamethasone (Dex). In contrast to our previous findings in vivo [Geisterfer et al., 1993, Cytokine, 5:1] in vitro Dex seemed to be the major stimulator of IL-6R mRNA expression, whereas IL-6 seemed to have little effect on the expression of its own receptor mRNA levels. However, the presence of other cytokines influenced the Dex mediated stimulation of IL-6R expression. OSM stimulated IL-6R mRNA levels. At 6 h, cells stimulated with OSM showed a 2.1-fold increase in IL-6R mRNA expression. This stimulation was additive with the Dex-mediated stimulation of IL-6R mRNA levels. In contrast, IL-1 inhibited the Dex-mediated stimulation of IL-6R mRNA. At the same time, IL-1 stimulated the presence of a second smaller mRNA transcript. This mRNA species contained the extracellular domain but lacked both the transmembrane and cytoplasmic domains of the IL-6R, suggesting alternate splicing, possibly coding for a soluble form of gp80. Unlike the gp80 IL-6R molecule, the expression of the gp130 molecule normally expressed as two species of mRNA was not regulated to any major extent in vitro. IL-1 and OSM stimulated both mRNA bands (7.5 and 9.0 kb) approximately 2-fold, whereas IL-6 stimulated mainly the upper 9.0 kb mRNA band.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenovirus vectors for cytokine gene expression

Recombinant Adenovirus type 5 constructs containing IL-6 cDNA can be used to infect cells in vitro and obtain a high level of IL-6 expression and secretion into culture media. Furthermore, Ad5-IL-6 viruses can also be used to infect Balb/c mice or Sprague-Dawley rats and obtain a high level of IL-6 expression that is sustained over a period of 3-5 days. Intratracheal infection was accompanied by dramatic increases in virus-encoded IL-6 mRNA levels in rat lung tissue, raised levels of IL-6 detected in bronchoalveolar lavage fluids and in serum, and IL-6-dependent sequelae such as liver acute phase responses. This occurs in a tissue-specific manner, depending on routes of infection by the virus. Rat lungs showed a prominent expansion (10 fold in numbers) of all classes of lymphocytes, including B cells, T helper cells (CD4+) and CTL (CD8+) at day 7 after infection which resolved significantly by day 12. Thus the associated biological effects of viral vector mediated IL-6 over-expression was also transient in nature. Other tissues can be infected with Ad5 and thus can also be induced to express selected genes in a transient fashion. We are currently examining the potential for Ad recombinant cytokine vectors in therapy for cancer and for bone marrow reconstitution after transplantation. Thus the use of recombinant Ad5 vectors may have a broad application in the study of cytokine function and possibly in future therapy as a transient gene transfer approach.

Prostanoid enhancement of interleukin-6 production by rat peritoneal mast cells

Mast cells are traditionally associated with an acute response involving the short-term release of mediators such as histamine. We have shown previously that mast cells can produce IL-6 without prior histamine release. In this study we examined the hypothesis that mast cell IL-6 production can be selectively regulated by PGs. Highly purified rat peritoneal mast cells were cultured in the presence of PGE1, PGE2, or PGD2 alone or in combination with anti-IgE or bacterial LPS. Histamine release was assessed after 10 min; IL-6 and TNF-alpha production was measured in supernatants after 18 h. Mast cell IL-6 production was induced by PGE1 and PGE2 to a similar level to that observed in anti-IgE-activated cells. In contrast, constitutive production of TNF-alpha was inhibited by PGE1 and PGE2, but not by PGD2. PGE2 had a synergistic effect, inducing IL-6 in the presence of LPS, whereas an additive effect was observed in the presence of anti-IgE. None of the prostanoids alone induced significant histamine release at the 10-min time point. However, PGE2 significantly increased histamine release when added concurrently with anti-IgE. Flurbiprofen in the context of anti-IgE or LPS activation did not alter mast cell IL-6 or TNF-alpha production. IL-6 production in response to each of the stimuli was significantly inhibited by the corticosteroid dexamethasone. These observations of selective modulation of mast cell cytokine production are important to understand the mechanisms by which mast cells interact with other cells during an inflammatory process involving prostanoid synthesis.

Prostanoid enhancement of interleukin-6 production by rat peritoneal mast cells

Mast cells are traditionally associated with an acute response involving the short-term release of mediators such as histamine. We have shown previously that mast cells can produce IL-6 without prior histamine release. In this study we examined the hypothesis that mast cell IL-6 production can be selectively regulated by PGs. Highly purified rat peritoneal mast cells were cultured in the presence of PGE1, PGE2, or PGD2 alone or in combination with anti-IgE or bacterial LPS. Histamine release was assessed after 10 min; IL-6 and TNF-alpha production was measured in supernatants after 18 h. Mast cell IL-6 production was induced by PGE1 and PGE2 to a similar level to that observed in anti-IgE-activated cells. In contrast, constitutive production of TNF-alpha was inhibited by PGE1 and PGE2, but not by PGD2. PGE2 had a synergistic effect, inducing IL-6 in the presence of LPS, whereas an additive effect was observed in the presence of anti-IgE. None of the prostanoids alone induced significant histamine release at the 10-min time point. However, PGE2 significantly increased histamine release when added concurrently with anti-IgE. Flurbiprofen in the context of anti-IgE or LPS activation did not alter mast cell IL-6 or TNF-alpha production. IL-6 production in response to each of the stimuli was significantly inhibited by the corticosteroid dexamethasone. These observations of selective modulation of mast cell cytokine production are important to understand the mechanisms by which mast cells interact with other cells during an inflammatory process involving prostanoid synthesis.

Anaesthetic modulation of nicotinic ion channel kinetics in bovine chromaffin cells

1. We have investigated the action of the anaesthetics methoxyflurane, methohexitone and etomidate on the nicotinic acetylcholine receptor channel of bovine adrenal chromaffin cells using the whole cell patch clamp technique. 2. Spectral analysis of macroscopic currents evoked by 25 microM carbachol revealed that each of the agents tested reduced the lifetime of the channel open state in a dose-dependent manner. The whole cell current was inhibited in a concentration-dependent fashion by each agent. 3. Channel gating parameters were calculated from single channel studies and the results used to test models explaining the modulation of nicotinic acetylcholine receptor channels by anaesthetics. 4. Each of the agents studied reduced the mean channel open time in a concentration-dependent manner. Anaesthetic concentrations reducing mean open time by 50% were: 370 microM methoxyflurane, 30 microM methohexitone or 23 microM etomidate. 5. Methohexitone and etomidate produced an increase in the number of brief closures within bursts, while no such increase was observed with methoxyflurane. Despite these inter-burst gaps, mean burst length was reduced by each of the agents tested. 6. It is concluded that a simple sequential blocking model fails to account for the action of these anaesthetics. An extended model, in which blocked channels can close, may be applicable.

The synaptic basis of general anaesthesia

The cellular and synaptic mechanisms that underpin the state of general anaesthesia are discussed. Anaesthetics act principally on synaptic processes and this provides a satisfactory basis for understanding their effects on neural networks. Although anaesthetics affect both the release of neurotransmitters and post-synaptic receptor function, the effects on post-synaptic receptors are always of importance in the modulation of synaptic transmission. Effects on action potential firing patterns also play a role in anaesthetic modulation of neuronal signalling. Many of these complex data can be explained in terms of altered ion channel function.

Calcium channel currents in bovine adrenal chromaffin cells and their modulation by anaesthetic agents

1. The calcium channel currents of bovine adrenal chromaffin cells were characterized using a variety of voltage pulse protocols and selective channel blockers before examination of their modulation by anaesthetic agents. 2. All the anaesthetics studied (halothane, methoxyflurane, etomidate and methohexitone) inhibited the calcium channel currents in a concentration-dependent manner and increased the rate of current decay. 3. The anaesthetics did not shift the current-voltage relation nor did they change the voltage for half-maximal channel activation derived from analysis of the voltage dependence of the tail currents. None of the anaesthetics appeared to alter the time constant of tail current decay. 4. To complement earlier studies of the inhibitory actions of anaesthetics on K(+)-evoked catecholamine secretion and the associated Ca2+ uptake, the IC50 values for etomidate and methohexitone were determined using a biochemical assay. The IC50 values for anaesthetic inhibition of calcium channel currents corresponded closely with those for inhibition of K(+)-evoked calcium uptake and catecholamine secretion. 5. The inhibitory effect of the volatile anaesthetics and etomidate is best explained by dual action: a reduction in the probability of channel opening coupled with an increase in the rate of channel inactivation. Methohexitone appeared to inhibit the currents by a use-dependent slow block.

Direct monitoring of dopamine and 5-HT release in substantia nigra and ventral tegmental area in vitro

Fast-scan cyclic voltammetry with carbon fibre microelectrodes was used to detect endogenous dopamine (DA) and 5-hydroxytryptamine (5-HT) release from three distinct regions of guinea-pig mid-brain in vitro: rostral and caudal substantia nigra (SN) and the ventral tegmental area (VTA). Previous electrophysiological studies have demonstrated that cells of the caudal SN and the VTA have similar characteristics, whereas cells in the rostral SN have distinctly different properties. In the present study, we confirmed that each region has tyrosine hydroxylase-positive neurons and determined, using high-performance liquid chromatography, that DA levels were similar in rostral and caudal SN, but lower in SN than in VTA. In each region, application of veratrine, which was shown by intracellular recordings to have a reversible depolarising action, evoked a signal attributable to DA and distinguishable from that of 5-HT. Release signals were monitored every 250 ms with a spatial resolution of less than 50 microns.l DA release was calcium-dependent and was not detectable in a catecholamine-poor area such as the cerebellum, or in mid-brain tissue pre-treated with reserpine. Within the normal mid-brain, the amount of DA released was correlated with tissue content in that it was higher in the VTA than in either region of SN. It is concluded that DA released from somato-dendritic parts of mid-brain neurons exhibits site-specific variation. This is the first report of direct monitoring of DA and 5-HT release from these regions with in situ electrodes and demonstrates the utility of fast-scan cyclic voltammetry to investigate the mechanisms and possible non-classical functions of somato-dendritic DA release.

Anchorage-independent colony growth of pulmonary fibroblasts derived from fibrotic human lung tissue

Fibroblast heterogeneity is known to exist in chronically inflamed tissue such as pulmonary fibrosis (IPF) and scleroderma. We have previously shown differences in proliferation rates in primary lines and cloned lines of fibroblasts derived from IPF tissue compared with normal lung. In this study, we report that cell lines derived from fibrotic tissue demonstrate anchorage-independent growth in soft agarose culture whereas normal lung fibroblast lines do not. We also show that fibroblast lines derived from neonatal lung tissue form colonies at about the same frequency as the fibrotic cells. Colonies from both fibrotic and neonatal lines were shown to be positive for vimentin, laminin, fibronectin, fibronectin receptor, beta-actin, and tropomyosin by immunohistochemistry but were negative for desmin, keratin, Factor VIII, alpha-smooth muscle cell actin, and tenascin. Treatment with cytokines TGF-beta and PDGF or with corticosteroid modified the colony-forming capacity of fibrotic and neonatal cell lines, however, none of these treatments induced normal lung cell lines to form colonies. The presence of cells in adult fibrotic tissue with growth characteristics similar to those exhibited by neonatal cells is further evidence of fibroblast heterogeneity and suggests newly differentiated fibroblasts may be prevalent in fibrotic tissue and contribute directly to the matrix disorder seen in this disease.

Properties of single calcium-activated potassium channels of large conductance in rat hippocampal neurons in culture

Patch-clamp recordings were made on rat hippocampal neurons maintained in culture. In cell-attached and excised inside-out and outside-out patches a large single-channel current was observed. This channel had a conductance of 220 and 100 pS in 140 mM [K+]i/140 mM [K+]o and 140 mM [K+]i/3 mM [K+]o respectively. From the reversal potential the channel was highly selective for K+, the PK+/PNa+ ratio being 50/1. Channel activity was voltage-dependent, the open probability at 100 nM [Ca2+]i increasing by e-fold for a 22 mV depolarization. It was also dependent on [Ca2+]i at both resting and depolarized membrane potentials. Channel open states were best described by the sum of two exponentials with time constants that increased as the membrane potential became more positive. Channel activity was sensitive to both external (500 microM) and internal (5 mM) tetraethylammonium chloride. These data are consistent with the properties of maxi-K+ channels described in other preparations, and further suggest a role for maxi-channel activity in regulating neuronal excitability at the resting membrane potential. Channel activity was not altered by 8-chlorophenyl thio cAMP, concanavalin A, pH reduction or neuraminidase. In two of five patches lemakalim (BRL 38227) increased channel activity. Internal ruthenium red (10 microM) blocked the channel by shortening the duration of both open states. This change in channel gating was distinct from the 'mode switching' seen in two patches, where a channel switched spontaneously from normal activity typified by two open states to a mode where only short openings were represented.

Interaction between oncostatin M, interleukin 1 and prostaglandin E2 in induction of IL-6 expression in human fibroblasts

The role of Oncostatin M (OM), a monocyte/macrophage and T-cell product, in regulating IL-6 expression in fibroblasts of lung or synovial origin was examined in vitro. Although by itself OM had a minimal effect on enhancing IL-6 production by fibroblasts, in combination with IL-1 alpha or PGE2, OM addition resulted in a dose-dependent synergistic enhancement of IL-6 production. This synergistic effect with either IL-1 alpha (5 ng/ml) or PGE2 (10(-7) M) was clearly evident at concentrations of OM of 10, 20 or 50 ng/ml. Levels of IL-6 resulting from OM and IL-1 alpha stimulation could be reduced by indomethacin (10(-6) M) and restored again by also adding PGE2. Northern blots probed for IL-6 mRNA showed cooperative enhancement of steady state levels at 18 hours of stimulation by OM and IL-1 alpha, or OM and PGE2. Probing for mRNA of the metalloproteinase inhibitor TIMP-1 showed that stimulation by OM, IL-1 alpha or PGE2 enhanced TIMP-1 levels. However, OM (alone) or PGE2 or both combined did not elevate the metalloproteinase stromelysin-1 mRNA signals. Analysis utilizing a rat IL-6 promoter-luciferase reporter gene construct showed that OM stimulation resulted in activation of transcription that synergistically enhanced IL-1-induced levels of reporter gene expression. These results show that although OM has minor effects on IL-6 production alone, the combination of OM and other mediators result in markedly enhanced IL-6 production by fibroblasts in vitro.

Construction of recombinant human type 5 adenoviruses expressing rodent IL-6 genes. An approach to investigate in vivo cytokine function

The majority of biologic functions assigned to cytokines have been characterized by in vitro assay systems which may not necessarily reflect cytokine roles in vivo. Recently, recombinant virus approaches have allowed tissue-specific expression of foreign gene products in experimental animal models. We have constructed recombinant human type 5 adenoviruses, deficient in the E3 region of the genome, with incorporated rodent IL-6 cDNA that express significant levels of biologically active IL-6 on infection both in vitro and in vivo. After i.p. injection, the liver, spleen, and peritoneum appear to be primary sites of expression, whereas the lung and bronchus are the main sites of expression after intratracheal instillation. Injection i.p. of BALB/c mice with the murine rIL-6 virus causes an increase in serum levels of bioactive IL-6 for up to 6 days post-infection, whereas similar changes are not seen in animals infected with control viruses. Coincident with enhanced plasma levels of IL-6, we detect raised serum levels of hepatic-derived acute phase proteins. Associated with the expression of IL-6 in the liver and spleen, at 7 days we note a fourfold splenomegaly with expansion of B and T cell compartments, as well as the presence of lymphoid aggregates in the liver. These morphologic changes had resolved by 16 days. Our findings demonstrate that recombinant human type 5 adenoviruses expressing cDNA for various cytokines could be used as a transient pseudo-transgenic animal model to investigate the biologic function of cytokines in vivo.

Construction of recombinant human type 5 adenoviruses expressing rodent IL-6 genes. An approach to investigate in vivo cytokine function

The majority of biologic functions assigned to cytokines have been characterized by in vitro assay systems which may not necessarily reflect cytokine roles in vivo. Recently, recombinant virus approaches have allowed tissue-specific expression of foreign gene products in experimental animal models. We have constructed recombinant human type 5 adenoviruses, deficient in the E3 region of the genome, with incorporated rodent IL-6 cDNA that express significant levels of biologically active IL-6 on infection both in vitro and in vivo. After i.p. injection, the liver, spleen, and peritoneum appear to be primary sites of expression, whereas the lung and bronchus are the main sites of expression after intratracheal instillation. Injection i.p. of BALB/c mice with the murine rIL-6 virus causes an increase in serum levels of bioactive IL-6 for up to 6 days post-infection, whereas similar changes are not seen in animals infected with control viruses. Coincident with enhanced plasma levels of IL-6, we detect raised serum levels of hepatic-derived acute phase proteins. Associated with the expression of IL-6 in the liver and spleen, at 7 days we note a fourfold splenomegaly with expansion of B and T cell compartments, as well as the presence of lymphoid aggregates in the liver. These morphologic changes had resolved by 16 days. Our findings demonstrate that recombinant human type 5 adenoviruses expressing cDNA for various cytokines could be used as a transient pseudo-transgenic animal model to investigate the biologic function of cytokines in vivo.

The expression of matrix metalloproteinases and their inhibitors by pig synovial cells and their regulation by combinations of cytokines and growth factors

1. Pig synovial fibroblasts in culture were studied to determine if they were an easily reproducible model system for studying the actions of cytokines and growth factors on human synovial cells. The biochemical analyses were conducted by activity assays, enzymography and Northern blot. 2. Human recombinant interleukin-1 alpha, basic fibroblast growth factor and transforming growth factor-beta 1 were studied in combinations because of their known involvement in controlling tissue remodelling. 3. The response of pig fibroblasts to these agents, in terms of the expression of matrix metalloproteinases (collagenase, gelatinase and stromelysin) and their inhibitors (TIMPs), show that they behave similarly enough to human cells for use when supplies of human primary cells are unavailable.

Excitatory and inhibitory synaptic mechanisms in anaesthesia

To understand the cellular and molecular basis of the anaesthetic state, it is important to remember that, in the intact CNS, synapses operate within elaborate nerve networks. From the data presented above, it is evident that block of impulse conduction in presynaptic fibres does not explain the effects of most anesthetics on synaptic activity. This is not surprising since some anaesthetics, the barbiturates in particular, may both depress excitation and enhance inhibition. General anaesthetics modulate the activity of presynaptic voltage-gated calcium channels and this appears to be sufficient to account for the reduction in transmitter secretion they produce. Transmitter operated ion channels in the postsynaptic membrane are modulated by smaller concentrations of anaesthetics than are required to modulate the presynaptic voltage-gated calcium channels. For this reason, transmitter operated channels appear to represent a major target site for anaesthetics. Finally, there are subtle effects of anaesthetics on the patterns of impulse propagation in nerve axons and on action potential generation in the cell body which result from modulation of membrane excitability. The overall effect of an anaesthetic agent depends on summation of events occurring at the many individual synapses and neurones that make up the network. The effects of anaesthetics on different neuronal pathways may therefore depend on the nature of the receptors and ion channels of the cells that comprise the network. The anaesthetic state may be the result of all these actions, but the characteristics of the state may differ somewhat from agent to agent.

Selective regulation of metalloproteinase inhibitor (TIMP-1) by oncostatin M in fibroblasts in culture

Tissue inhibitor of metalloproteinases (TIMP-1) is a potent inhibitor of activated matrix metalloproteinases (MMP) such as collagenase, stromelysin, and gelatinase, and thus helps to control extracellular matrix metabolism and deposition by connective tissue cells. Since various cytokines and growth factors can modify the production of MMP and TIMP-1, we explored the action of oncostatin M (OM), a unique lymphocyte- and monocyte-derived cytokine, on expression of these proteins. We examined the regulation of TIMP-1 expression in cultured human fibroblasts by cytokines including OM, IL-6, leukemia inhibitory factor (LIF), and IL-1 alpha. When used at levels of 5 to 50 ng/ml, OM, IL-6, LIF, and IL-1 alpha elevated the TIMP-1 expression at the RNA level in fibroblasts of lung or synovial origin. Interestingly, OM stimulation resulted in highest levels of TIMP-1 RNA and protein synthesis. However, unlike IL-1 alpha, the cytokines OM, IL-6, and LIF did not induce MMP or PGE2 release. OM also enhanced TIMP-1 mRNA levels in the H2981 lung carcinoma and HepG2 hepatoma cell lines. The results suggest that OM as well as IL-6 and LIF, other cytokines acting through similar receptor pathways, may act to inhibit net MMP activity by specifically up-regulating TIMP-1 expression. The selective induction of TIMP-1 by OM may be influential in altering matrix destruction in chronic inflammation and tumor metastasis.

Selective regulation of metalloproteinase inhibitor (TIMP-1) by oncostatin M in fibroblasts in culture

Tissue inhibitor of metalloproteinases (TIMP-1) is a potent inhibitor of activated matrix metalloproteinases (MMP) such as collagenase, stromelysin, and gelatinase, and thus helps to control extracellular matrix metabolism and deposition by connective tissue cells. Since various cytokines and growth factors can modify the production of MMP and TIMP-1, we explored the action of oncostatin M (OM), a unique lymphocyte- and monocyte-derived cytokine, on expression of these proteins. We examined the regulation of TIMP-1 expression in cultured human fibroblasts by cytokines including OM, IL-6, leukemia inhibitory factor (LIF), and IL-1 alpha. When used at levels of 5 to 50 ng/ml, OM, IL-6, LIF, and IL-1 alpha elevated the TIMP-1 expression at the RNA level in fibroblasts of lung or synovial origin. Interestingly, OM stimulation resulted in highest levels of TIMP-1 RNA and protein synthesis. However, unlike IL-1 alpha, the cytokines OM, IL-6, and LIF did not induce MMP or PGE2 release. OM also enhanced TIMP-1 mRNA levels in the H2981 lung carcinoma and HepG2 hepatoma cell lines. The results suggest that OM as well as IL-6 and LIF, other cytokines acting through similar receptor pathways, may act to inhibit net MMP activity by specifically up-regulating TIMP-1 expression. The selective induction of TIMP-1 by OM may be influential in altering matrix destruction in chronic inflammation and tumor metastasis.

The action of anaesthetics on stimulus-secretion coupling and synaptic activity

1. Anaesthetics are known to depress excitatory synaptic transmission and the mechanism of this inhibition has been investigated using bovine adrenal chromaffin cells as an experimental model. 2. These cells are homologous with post-ganglionic sympathetic neurons and have well characterized receptor and secretory mechanisms. They are amenable both to the direct measurement of evoked secretion with its associated ion fluxes, and to electrophysiological investigation using the patch clamp technique. 3. These approaches have been used to study the influence of anaesthetics on pre- and post-synaptic mechanisms involved in stimulus-secretion coupling. 4. A variety of agents inhibited secretion evoked by direct depolarization, and this was shown to be due to a reduction in calcium influx. 5. Direct inhibition of voltage-gated calcium currents was confirmed by whole-cell patch clamp measurements. 6. In addition, anaesthetics powerfully modulated nicotinic receptor mediated events: carbachol-evoked secretion was more sensitive to anaesthetics than that stimulated by high potassium. 7. The mechanism of anaesthetic action on the nAChR was examined in more detail with patch-clamp experiments. 8. These showed that anaesthetics reduced the probability of channels being in the open state, largely as a result of reduction in mean channel open time. 9. The data are discussed in relation to excitatory synaptic transmission.

The mechanism by which procaine inhibits catecholamine secretion from bovine chromaffin cells

1. We have investigated the action of procaine on stimulus-secretion coupling in bovine adrenal chromaffin cells. 2. Procaine inhibited the catecholamine secretion evoked by 500 microM carbachol (CCh) with an IC50 of 35 microM and the associated calcium influx (IC50 60 microM). It inhibited the catecholamine secretion evoked by depolarization with high potassium by less than 20% even at the highest concentrations tested (3.2 mM). 3. The secretion evoked by CCh was associated with an increase in sodium influx. This evoked influx was also inhibited by procaine (IC50 80 microM). 4. This selective action of procaine on the CCh-evoked catecholamine secretion was investigated further by patch-clamp techniques. 5. In agreement with the ion flux studies, procaine inhibited the inward current evoked by CCh. Procaine also altered the spectral characteristics of the noise associated with the agonist-induced current by adding an additional high frequency component. The amplitude of this component showed an e-fold increase for a 55 mV membrane hyperpolarization. 6. Data from cell-attached patches showed that increasing concentrations of procaine produced a progressive fall in the mean channel open time and an increase in mean blocked time. This combination led to a decrease in mean burst length. In addition, Popen was reduced by 50 microM procaine. These changes in channel conducting time were sufficient to account for the reduction in inward current. A limited study of the action of procaine on nicotinic channels in outside-out patches gave similar results. 7. The data were considered in relation to various schemes of anaesthetic-channel interactions. The data did not fit the sequential blocking model or the extended channel block model but could be fitted to a modified sequential blocking model in which the rate constant for channel reopening after block was itself subject to modulation by the anaesthetic and the blocked channel could close without passing through the open state.

Recombinant oncostatin M stimulates the production of acute phase proteins in HepG2 cells and rat primary hepatocytes in vitro

Acute inflammation is characterized by increased liver output of acute phase proteins (APP). Several cytokines including IL-6, leukemia inhibitory factor, and IL-11 are capable of stimulating APP synthesis by hepatocytes and hepatoma cells. We have tested the activity of a separate and unique cytokine oncostatin M (OM) and have found potent APP-inducing activity of human recombinant OM on hepatocytes. OM acted in a dose-dependent fashion (ED50 5 to 10 ng/ml) in stimulating APP synthesis in human HepG2 cells, rat H35 cells, and primary rat hepatocyte cultures, but not human Hep3B cells. Human OM induced equivalent to or greater responses than IL-6 in HepG2 cells, however, it was less effective than human IL-6 in stimulating rat cells. Northern analysis showed that OM stimulated mRNA levels of haptoglobin and alpha 1-antichymotrypsin in HepG2 cells. OM induced CAT activity in HepG2 cells transfected with CAT constructs containing IL-6-responsive elements, suggesting that OM induces transcription of native proteins through mechanisms involving IL-6-responsive element-like sequences in gene promoters. OM was also shown to act additively with IL-6 or leukemia inhibitory factor and synergistically with glucocorticoid or IL-1 in the induction of specific APP. These results suggest that OM plays a role as a mediator of APP synthesis in inflammatory responses.

Recombinant oncostatin M stimulates the production of acute phase proteins in HepG2 cells and rat primary hepatocytes in vitro

Acute inflammation is characterized by increased liver output of acute phase proteins (APP). Several cytokines including IL-6, leukemia inhibitory factor, and IL-11 are capable of stimulating APP synthesis by hepatocytes and hepatoma cells. We have tested the activity of a separate and unique cytokine oncostatin M (OM) and have found potent APP-inducing activity of human recombinant OM on hepatocytes. OM acted in a dose-dependent fashion (ED50 5 to 10 ng/ml) in stimulating APP synthesis in human HepG2 cells, rat H35 cells, and primary rat hepatocyte cultures, but not human Hep3B cells. Human OM induced equivalent to or greater responses than IL-6 in HepG2 cells, however, it was less effective than human IL-6 in stimulating rat cells. Northern analysis showed that OM stimulated mRNA levels of haptoglobin and alpha 1-antichymotrypsin in HepG2 cells. OM induced CAT activity in HepG2 cells transfected with CAT constructs containing IL-6-responsive elements, suggesting that OM induces transcription of native proteins through mechanisms involving IL-6-responsive element-like sequences in gene promoters. OM was also shown to act additively with IL-6 or leukemia inhibitory factor and synergistically with glucocorticoid or IL-1 in the induction of specific APP. These results suggest that OM plays a role as a mediator of APP synthesis in inflammatory responses.

Effects of pentobarbitone on the properties of nicotinic channels of chromaffin cells

We have used the whole cell patch clamp technique to investigate the action of pentobarbitone on the nicotinic channels of bovine chromaffin cells. Application of agonists induced an inward current associated with a large increase in current noise. The noise could be fitted by Lorentzian functions with time constants of 17 +/- 2 ms for 10 microM acetylcholine and 10 +/- 1 ms for 10 microM carbachol. The single channel conductance estimated from the current variance was about 25 pS in each case. Pentobarbitone decreased the time constants in a concentration-dependent fashion, but the unit conductances were unaffected. Single channel events were recorded in chromaffin cells held under voltage clamp. Pentobarbitone did not reduce the amplitude of channel openings or the probability of channel opening but reduced the mean channel open time. This reduction was sufficient to account for the decrease in inward current produced by pentobarbitone.