Persistent tumor necrosis factor signaling in normal human fibroblasts prevents the complete resynthesis of I kappa B-alpha.

Transcription factor NF-kappa B is normally sequestered in the cytoplasm, complexed with I kappa B inhibitory proteins. Tumor necrosis factor (TNF) and interleukin-1 induce I kappa B-alpha phosphorylation, leading to I kappa B-alpha degradation and translocation of NF-kappa B to the nucleus where it activates genes important in inflammatory and immune responses. TNF and interleukin-1 actions are typically terminated by desensitization, and I kappa B-alpha reappearance normally occurs within 30-60 min. We found that in normal human FS-4 fibroblasts maintained in the presence of TNF, I kappa B-alpha protein failed to return to base-line levels for up to 15 h. Removal of TNF at any time during the 15-h period resulted in complete I kappa B-alpha resynthesis, suggesting that I kappa B-alpha reappearance was prevented by continued TNF signaling. Long term exposure of FS-4 fibroblasts to TNF led to a persistent presence of I kappa B-alpha mRNA, sustained I kappa B kinase activation, continuous proteasome-mediated degradation of I kappa B-alpha, and sustained nuclear localization of NF-kappa B. Continuous exposure of FS-4 cells to TNF did not lead to a sustained activation of p38 or ERK mitogen-activated protein kinases, suggesting that not all TNF-induced signaling pathways are persistently activated. These findings challenge the notion that all cytokine-mediated signals are rapidly terminated by desensitization and illustrate the need to elucidate the process of deactivation of TNF-induced signaling.

TNF/IL-1-inducible protein TSG-6 potentiates plasmin inhibition by inter-alpha-inhibitor and exerts a strong anti-inflammatory effect in vivo.

TNF-stimulated gene 6 (tsg6), encoding a 35-kDa secretory glycoprotein (TSG-6), is induced in fibroblasts, chondrocytes, synovial cells, and mononuclear cells by the proinflammatory cytokines TNF-alpha and IL-1, or by LPS. Large amounts of TSG-6 protein were found in synovial fluids of patients with rheumatoid arthritis. TSG-6 protein forms a stable complex with components of the serine protease inhibitor, inter-alpha-inhibitor (I alpha I). In this work, we show that TSG-6 potentiates the inhibitory effect of l alpha l on the protease activity of plasmin. The plasmin/plasminogen activator system is important in the protease network associated with inflammation. To test the hypothesis that through their cooperative inhibitory effect on plasmin TSG-6 and l alpha l can modulate the protease network and thus inhibit inflammation, we examined the effect of TSG-6 on experimentally induced inflammation. Human recombinant TSG-6 protein showed a potent anti-inflammatory activity in the murine air pouch model of carrageenan- or IL-1-induced acute inflammation. The inhibitory effect of locally administered TSG-6 on the IL-1-induced cellular infiltration was comparable with that of systemic dexamethasone treatment. Two mutant TSG-6 proteins with single amino acid substitutions close to the N terminus showed a complete or partial loss of anti-inflammatory activity. The anti-inflammatory effect of the TNF/IL-1-inducible TSG-6 protein, along with its ability to inhibit protease action through interaction with l alpha l, suggests that TSG-6 production during inflammation is part of a negative feedback loop operating through the protease network.

The general anesthetic potency of propofol and its dependence on hydrostatic pressure.

Although plasma concentrations of propofol during anesthesia are well known, the free concentration remains unknown because of uncertainties regarding plasma protein binding, interaction with other protein-bound substances, the level of binding to its lipid carrier, and the use of adjuvants. At elevated surrounding pressure, all general anesthetics require higher concentrations to reach adequate levels of anesthesia. To determine the anesthetic potency of propofol at equilibrium conditions and to study the effects of pressure on propofol-induced anesthesia, Rana pipiens tadpoles were exposed to different concentrations of pure, not emulsified, propofol in aqueous solution. Anesthesia was defined as loss of the righting reflex. Ten animals per concentration were used, and each experiment was conducted twice. Pressure experiments were performed with nonanesthetized tadpoles and urethane-anesthetized tadpoles as control groups. Propofol concentrations were measured spectrophotometrically. At 1 atmosphere absolute (atm abs), a semilogarithmic sigmoidal concentration-response curve was obtained with a half-maximal effect of propofol at 2.2 +/- 0.22 microM (EC50; mean +/- SE). Increased pressure shifted the concentration-response curve to the right. The EC50 increased linearly with increasing pressure up to 121 atm abs (EC50 at 121 atm abs = 4.1 +/- 0.41 microM). For pressure greater than 121 atm abs, an increased excitability of the tadpoles made it difficult to distinguish the righting reflex from involuntary movements. The saturated solubility of propofol in aqueous solution was found to be 1.0 +/- 0.02 mM (mean +/- SD), and the octanol/water partition coefficient was 4,300 +/- 280. Propofol adhered to the correlation between anesthetic potency and octanol/water partition coefficient exhibited by other general anesthetics.(ABSTRACT TRUNCATED AT 250 WORDS)

The temperature dependence of some kinetic and conductance properties of acetylcholine receptor channels.

We examined the temperature dependence of single-channel properties of the nicotinic acetylcholine receptor channel from clonal BC3H-1 cells over a range of 10-40 degrees C. We found temperature sensitivities (Q10 values) of 2-4 for the mean channel open time. The Q10 did not depend strongly on voltage and the voltage dependence of the mean open time was temperature-independent. The Q10 of closing rate of the long-lived open state was 3-4 but the Q10 of closing rate of the brief open state was independent of temperature. The duration of brief closures could be measured only between 10 and 25 degrees C. Since this approached the limit of the experimental time resolution, an accurate determination of the Q10 could not be made. The current decay due to desensitization after rapid application of high concentrations of agonist varied with a Q10 of about 2. The conductance of single channels (the inverse of the ion translocation rate) had a Q10 of 1.3-1.5. We found no obvious nonlinearities in the Arrhenius curves for any of the measured properties.