Plasmin and the regulation of tissue-type plasminogen activator biosynthesis in human endothelial cells.

Plasmin inhibited the biosynthesis of tissue-type plasminogen activator (tPA) antigen by human umbilical vein endothelial cells (HUVEC) in a dose-dependent manner. The amount of tPA antigen found in the 24-h conditioned medium of cells treated with 100 nM plasmin for 1 h was 20-30% of that in the control group. However, in contrast to tPA, such treatment led to a 3-fold increase in plasminogen activator inhibitor (PAI) activity, whereas the amount of PAI type 1 antigen was unchanged. The effects of plasmin on HUVEC were binding- and catalytic activity-dependent and were specifically blocked by epsilon-aminocaproic acid. Microplasmin, which has no kringle domains, was less effective in reducing tPA antigen biosynthesis or enhancing PAI activity in HUVEC. Kringle domains of plasmin affected neither tPA antigen nor PAI activity of the cells. Other proteases including chymotrypsin, trypsin, and collagenase at comparable concentrations did not have a significant effect on the biosynthesis of tPA antigen or PAI activity of HUVEC. Thrombin stimulated the biosynthesis of tPA and PAI-1 antigens by HUVEC. Thrombin also stimulated an increase in the protein kinase activity in HUVEC, whereas plasmin inhibited the protein kinase activity of the cells. It is possible that plasmin regulates the biosynthesis of tPA in HUVEC through the signal transduction pathway involving protein kinase.     

Photoinhibition of photosynthesis represents a mechanism for the long-term regulation of photosystem II

The obligate shade plant, Tradescantia albiflora Kunth grown at 50 mol photons · m^–2 s^–1 and Pisum sativum L. acclimated to two photon fluence rates, 50 and 300 mol · m^–2 · s^–1, were exposed to photoinhibitory light conditions of 1700 mol · m^–2 · s^–1 for 4 h at 22° C. Photosynthesis was assayed by measurement of CO₂-saturated O₂ evolution, and photosystem II (PSII) was assayed using modulated chlorophyll fluorescence and flash-yield determinations of functional reaction centres. Tradescantia was most sensitive to photoinhibition, while pea grown at 300 mol · m^–2 · s^–1 was most resistant, with pea grown at 50 mol · m^–2 · s^–1 showing an intermediate sensitivity. A very good correlation was found between the decrease of functional PSII reaction centres and both the inhibition of photosynthesis and PSII photochemistry. Photoinhibition caused a decline in the maximum quantum yield for PSII electron transport as determined by the product of photochemical quenching (q_p) and the yield of open PSII reaction centres as given by the steady-state fluorescence ratio, F_vF_m, according to Genty et al. (1989, Biochim. Biophys. Acta 990, 81–92). The decrease in the quantum yield for PSII electron transport was fully accounted for by a decrease in F_vF_m, since q_p at a given photon fluence rate was similar for photoinhibited and noninhibited plants. Under lightsaturating conditions, the quantum yield of PSII electron transport was similar in photoinhibited and noninhibited plants. The data give support for the view that photoinhibition of the reaction centres of PSII represents a stable, long-term, down-regulation of photochemistry, which occurs in plants under sustained high-light conditions, and replaces part of the regulation usually exerted by the transthylakoid pH gradient. Furthermore, by investigating the susceptibility of differently lightacclimated sun and shade species to photoinhibition in relation to q_p, i.e. the fraction of open-to-closed PSII reaction centres, we also show that irrespective of light acclimation, plants become susceptible to photoinhibition when the majority of their PSII reaction centres are still open (i.e. primary quinone acceptor oxidized). Photoinhibition appears to be an unavoidable consequence of PSII function when light causes sustained closure of more than 40% of PSII reaction centres.Abbreviations F_o and F_o minimal fluorescence when all PSII reaction centres are open in darkness and steady-state light, respectively - F_m and F_m maximal fluorescence when all PSII reaction centres are closed in darkand light-acclimated leaves, respectively - F_v variable fluorescence - (F_m-F_o) under steady-state light con-ditions - F_s steady-state fluorescence in light - Q_A the primary,stable quinone acceptor of PSII - q_Ne non-photochemical quench-ing of fluorescence due to high energy state - (pH); q_Ni non-photochemical quenching of fluorescence due to photoinhibition - q_p photochemical quenching of fluorescence To whom correspondence should be addressedThis work was supported by the Swedish Natural Science Research Council (G.Ö.) and the award of a National Research Fellowship to J.M.A and W.S.C. We thank Dr. Paul Kriedemann, Division of Forestry and Forest Products, CSIRO, Canberra, Australia, for helpful discussions.     

Experimental hydroxyapatite cement cranioplasty.

Hydroxyapatite cement is a calcium phosphate-based material that when mixed with water forms a dense paste that sets within 15 minutes and isothermically converts in vivo to a microporous hydroxyapatite implant. This cement was used to reconstruct bilateral 2.5-cm-diameter full-thickness critical-sized parietal skull defects in six cats. One side was reconstructed with 100 percent hydroxyapatite cement, and the other with a mixture of 50 percent hydroxyapatite cement and 50 percent ground autogenous bone by weight. These animals were sacrificed at 6 and 12 months after implantation. Positive and negative controls also were prepared. The anatomic contour of the soft tissue overlying all hydroxyapatite cement implants was well maintained, there were no wound infections or structural failures, and the implants were well tolerated histologically. None of the negative (unreconstructed) control defects was completely filled with repair bone, and all positive (methyl methacrylate) controls demonstrated foreign-body giant-cell formation and fibrous encapsulation of the implants. Examination of decalcified and undecalcified sections revealed progressive but variable replacement of the cement by new bone and soft tissue without a change in the shape or volume of the hydroxyapatite cement-reconstructed areas. New bone comprised 77.3 and 64.7 percent of the tissue replacing the hydroxyapatite cement and hydroxyapatite cement-bone implants, respectively. Replacement of the hydroxyapatite cement implants by new bone is postulated to occur by a combination of osteoconduction and implant resorption. These results indicate that further experimental research leading to the possible application of hydroxyapatite cement for full-thickness calvarial defect reconstruction in humans is warranted.     

A cytoplasmic chaperonin that catalyzes beta-actin folding.

We have isolated a cytoplasmic chaperonin based on its ability to catalyze the folding of denatured beta-actin. The cytoplasmic chaperonin is organized as a multisubunit toroid and requires Mg2+ and ATP for activity. The folding reaction proceeds via the rapid ATP-independent formation of a binary complex, followed by a slower ATP-dependent release of the native product. Electron microscopic observations reveal a striking structural change that occurs upon addition of Mg2+ and ATP. The eukaryotic cytoplasm thus contains a chaperonin that is functionally analagous to its prokaryotic, mitochondrial, and chloroplastic counterparts.     

The nucleotide sequence of rabbit liver transferrin cDNA

The cDNA sequence of rabbit liver transferrin has been determined. The largest cDNA was 2279 base pairs (bp) in size and encoded 694 amino acids consisting of a putative 19 amino acid signal peptide and 675 amino acids of plasma transferrin. The deduced amino acid sequence of rabbit liver transferrin shares 78.5% identity with human liver transferrin and 69.1% and 44.8% identity with porcine and Xenopus transferrins, respectively. At the amino acid level, vertebrate transferrins share 26.4% identity and 56.5% similarity. The most conserved regions correspond to the iron ligands and the anion binding region. Optimal alignment of transferrin sequences required the insertion of a number of gaps in the region corresponding to the N-lobe. In addition, the N-lobes of transferrins share less amino acid sequence similarity than the C-lobes.     

Lipid-alginate interactions render changes in phospholipid bilayer permeability

Lipid vesicles, e.g. liposomes, generally release their contents in a continuous manner. However, when these vesicles are entrapped in Ca-alginate and coated with poly(L-lysine), they release their contents in an unusual fashion, in 'bursts'. Molecular-level studies indicated that lipid-alginate interactions are responsible for changes in the barrier properties of lipid vesicles. Differential scanning calorimetry revealed that exposure of liposomes to alginate resulted in a 4-fold reduction in the phase transition enthalpy, with no change in the melting temperature. Size-exclusion chromatography of liposomes-in-alginate gave an additional liposomal peak with a smaller elution volume. These studies suggested that alginate is inserted into the lipid bilayer of vesicles. Lipid-alginate interactions were highly dependent on phospholipid head group charge and the phase transition temperature of the phospholipid. Based on these interactions, a mechanism to explain the 'burst' from these entrapped liposomes is suggested.     

The effect of cyclooxygenase inhibition on the indices of the thrombocyte-vascular link in hemostasis and on the free-radical processes of lipid oxidation in experimental Salmonella intoxication]

Injection of Salmonella typhimurium endotoxin to the laboratory animals (rabbits) in dose of 1 mg/ml (LD84) induces the particular changes in the thrombocyte vessels system of hemostasis: decrease of aggregatory ability of thrombocytes, increase of thromboxane A2 and prostacyclin activation of lipid peroxidation process. Use of indomethacin--the cyclooxygenase inhibitor--leads to less progressive alterations of the studied parameters of the thrombocyte vessels hemostasis and lipid peroxidation processes.     

Volume elasticity of the ocular avascular compartment in vivo and post mortem

By considering the frequency dependence of the ocular volume elasticity it is possible to locate the static volume elasticity function of the avascular compartment of the eye in vivo. The procedure used involved measuring the dynamic volume elasticity function E=f(P, v), where E=volume elasticity, P=intraocular pressure, and v=frequency, in vivo and post mortem at a frequency higher than the apparent upper mechanical response frequency of the intraocular vascular bed. In addition, post mortem measurements were made of the volume elasticity function at a frequency which was as low as experimentally possible. For practical purposes the latter volume elasticity function may serve as an estimate of the static elasticity function of the avascular compartment in vivo. This is possible in all cases because at the high frequency level the dynamic volume elasticity functions measured in vivo and post mortem are identical.Partly presented by the first author at the 4th Mackenzie Symposium, Stirling 1977Decaased 18.3. 1980