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Abstract. The adhesion and migration of human diploid fibroblasts on plasma clots were measured. The role of plasma fibronectin was examined by depleting plasma of fibronectin before clotting. Fibronectin was not essential for cell adhesion and spreading, although rates were slightly slower on depleted dots. Rates of migration on the surface of clots were unaffected by fibronectin depletion.In contrast, fibronectin was an absolute requirement for migration of cells into plasma clots. Cells migrated rapidly into control clots but completely failed to penetrate the surface of fibronectin-depleted clots. The effect of depletion could only be reversed by adding fibronectin to depleted plasma before clotting. Adsorption of fibronectin after dotting failed to reverse the effect of depletion, suggesting that fibronectin had to be cross-linked by transglutaminase during the clotting process.

SUMMARYSynovial fluid from rabbit elbow, shoulder, hip and knee was analysed to establish the normal levels of parameters relevant to fluid exchange -viz. fluid mass per joint, hydraulic pressure, temperature, colloid osmotic pressure (COP), protein, albumin and glycosaminoglycan (GAG) concentrations. Fluid mass was greatest in the least congruous joint, the shoulder (43 + 4 mg), cf. 6 + 2 mg in the highly congruous hip. In the knee (24+4 mg) the mean thickness of the fluid layer was calculated to be 30,m. Fluid pressure was subatmospheric in all joints (mean -2-8+0-4cmH20, elbow, to -5-7+0-3cmH20, knee), as in many other interstitial spaces.Colloid osmotic pressure was substantial (mean 114+0-9cmH2O, shoulder, to 131+10 cmH20, elbow), being 40-46 % of serum level. Comparison of synovial fluid results with COP versus concentration curves in vitro indicated that the fluid's COP was primarily generated by its protein content (22-30 g 1-1, 64 % albumin) rather than GAG (4 0-5 8 g 1-1). The GAG was 95 % hyaluronate and 5 % sulphated GAG. Algebraic summation of the hydraulic and colloid osmotic pressures of synovial fluid and serum indicated a net filtration gradient from blood to joint cavity. When serum COP was reduced by intravenous saline infusion, synovial fluid mass increased, in accordance with the ultrafiltration hypothesis of synovial fluid formation. The fluid's colloid concentration declined as volume increased. The relation was not a simple dilution curve, but indicated that the newly formed synovial fluid contained > 8 g protein 1-1 (14-5 % serum concentration); and that hyaluronate was entering the synovial cavity at a rate of > 6 5 ,ug h-' per joint.

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Experimental and theoretical results in support of nonlinear dynamic behavior of photosynthetic reaction centers under light-activated conditions are presented. Different conditions of light adaptation allow for preparation of reaction centers in either of two different conformational states. These states were detected both by short actinic flashes and by the switching of the actinic illumination level between different stationary state values. In the second method, the equilibration kinetics of reaction centers isolated from Rhodobacter sphaeroides were shown to be inherently biphasic. The fast and slow equilibration kinetics are shown to correspond to electron transfer (charge separation) at a fixed structure and to combined electron-conformational transitions governed by the bounded diffusion along the potential surface, respectively. The primary donor recovery kinetics after an actinic flash revealed a pronounced dependence on the time interval (deltat) between cessation of a lengthy preillumination of a sample and the actinic flash. A pronounced slow relaxation component with a decay half time of more than 50 s was measured for deltat > 10 s. This component corresponds to charge recombination in reaction centers for which light-induced structural changes have not relaxed completely before the flash. The amplitude of this component depended on the conditions of the sample preparation, specifically on the type of detergent used in the preparation. The redox potential parameters as well as the structural diffusion constants were estimated for samples prepared in different ways.

Singlet oxygen (1O2) generation in the reaction centers (RCs) of Rhodobacter sphaeroides wild type was characterized by luminescent emission in the near infrared region (time resolved transients and emission spectra) and quantified to have quantum yield of 0.03 +/- 0.005. 1O2 emission was measured as a function of temperature, ascorbate, urea and potassium ferricyanide concentrations and as a function of incubation time in H2O:D2O mixtures. 1O2 was shown to be affected by the RC dynamics and to originate from the reaction of molecular oxygen with two sources of triplets: photoactive dimer formed by singlet-triplet mixing and bacteriopheophytin formed by direct photoexcitation and intersystem crossing.

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Human diploid fibroblasts were seeded onto or into plasma clots and different aspects of cell adhesion and migration were measured. The roles of plasminogen activators and plasmin were studied by either the removal of plasminogen from plasma prior to clotting or by the addition of 10 mM epsilon-aminocaproic acid, which brings about an inhibition of plasmin in this system. When cells were seeded onto the surface of plasma clots, rates of attachment, spreading, and migration were unaffected by plasminogen depletion or plasmin inhibition. In contrast, when cells were seeded into plasma clots, then, although the rates of cells spreading were unaffected, cell migration was abolished by plasminogen depletion or by plasmin inhibition. When cells were seeded onto the surface of plasma clots and the rate of migration into the clots was measured, there was an absolute requirement for plasmin activity; while fibroblasts migrated rapidly into the fibrin lattice of control clots, in the case of plasminogen-depleted clots, cells failed to penetrate the lattice. Focussing through a plasma clot revealed that fibroblasts do not migrate through the fibrin lattice but instead, localized areas of fibrinolysis are generated and cells migrate over the surface of the area of lysis.