Modelling biological gel contraction by cells: mechanocellular formulation and cell traction force quantification

Traction forces developed by most cell types play a significant role in the spatial organisation of biological tissues. However, due to the complexity of cell-extracellular matrix interactions, these forces are quantitatively difficult to estimate without explicitly considering cell properties and extracellular mechanical matrix responses. Recent experimental devices elaborated for measuring cell traction on extracellular matrix use cell deposits on a piece of gel placed between one fixed and one moving holder. We formulate here a mathematical model describing the dynamic behaviour of the cell-gel medium in such devices. This model is based on a mechanical force balance quantification of the gel visco-elastic response to the traction forces exerted by the diffusing cells. Thus, we theoretically analyzed and simulated the displacement of the free moving boundary of the system under various conditions for cells and gel concentrations. This model is then used as the theoretical basis of an experimental device where endothelial cells are seeded on a rectangular biogel of fibrin cast between two floating holders, one fixed and the other linked to a force sensor. From a comparison of displacement of the gel moving boundary simulated by the model and the experimental data recorded from the moving holder displacement, the magnitude of the traction forces exerted by the endothelial cell on the fibrin gel was estimated for different experimental situations. Different analytical expressions for the cell traction term are proposed and the corresponding force quantifications are compared to the traction force measurements reported for various kind of cells with the use of similar or different experimental devices.     

Effects of Al3+ and Be2+ ions combined with NaF on ciliary process adenylyl cyclase activity and aqueous humor dynamics in the rabbit eye

PURPOSE: The activity of Al3+, Ga3+, and Be2+ ions in the presence of NaF to directly activate G-proteins was investigated by their potentiative effect on forskolin (FSK)-activated adenylyl cyclase in rabbit ciliary process membranes and their effects on aqueous humor dynamics in vivo. METHODS: Adenylyl cyclase (AC) was determined by radiometric conversion of ATP to cAMP by the particulate fraction of rabbit ciliary processes. Intravitreal injections of sterile solutions of analytical grade salts were made into the center of the vitreous in a volume of 20 microliters. Intraocular pressure, aqueous humor flow, and uveoscleral outflow measurements were made by pneumatonometry, fluorophotometry, and fluorescein-dextran method, respectively. Outflow facility was determined by tonography in the intact eyes and by two-level constant pressure perfusion in cannulated eyes. RESULTS: Both Al3+ (EC50, 40 mumol/l) and Be2+ (EC50, 11 mumol/l) in the presence of 0.5-2 mM NaF activated the stimulatory G-protein Gs. Ga3+ was ineffective and did not antagonize the activation by Al3+. Intravitreal injections of Al3+ (1 mumol/eye) or Be2+ (0.5 or 1 mumol/eye) had no significant intraocular pressure (IOP) effect, nor did 1.5 or 3 mumol/eye of NaF, but when either cation was injected together with NaF, IOP decreased by up to 40% for up to 140 hr. At the time of maximum IOP effect (72 hr) aqueous humor flow determined by fluorophotometry was decreased in BeCl2+ NaF-treated eyes by 40% relative to BeCl2-treated eyes; however, tonographic facility of outflow was unaffected. Uveoscleral flow was also decreased by 38% in BeCl2+ NaF treated eyes. CONCLUSIONS: These findings support the hypothesis that Gs activation of ciliary process adenylyl cyclase decreases aqueous humor formation rate in rabbit eyes, and that activation of G-proteins mediates contraction of ciliary muscles causing a decrease of aqueous humor outflow via the uveoscleral route. The results suggest that G-proteins putatively involved in trabecular facility changes are less sensitive to activation by BeF3- than are other parameters of aqueous humor dynamics.     

Arteriovenous malformation presenting as a complex pelvic mass with ureteral obstruction. A case report

BACKGROUND: Arteriovenous malformations (AVMs) are an abnormal communication between arterial and venous structures. Pelvic AVMs have been infrequently described in the literature and represent an uncommon cause of a palpable pelvic mass. CASE: A case of pelvic AVM with ureteral obstruction occurred. The location and radiologic appearance of the AVM suggested a complex adnexal mass. During exploration and resection of the mass, significant bleeding was encountered. The diagnosis of AVM was made only retrospectively, with histologic examination of the specimen. CONCLUSION: AVMs are an uncommon and unique cause of pelvic pathology. Preoperative diagnosis will alert the surgeon as to the technically difficult resection that may be encountered and to the massive bleeding that can be associated with their removal.     

Tuberculosis associated haemophagocytic syndrome: two cases with a favourable outcome

Haemophagocytic syndrome is a heterogenous disease characterized by disordered macrophage activation associated with viral, bacterial or parasitic infection. The few reports of haemophagocytosis occurring in the presence of mycobacterial infection show a high mortality rate and we present two further cases notable for their favourable issue. Rapidity of diagnosis and immediate treatment could explain the avoidance of a fatal outcome.     

Late effects of radiotherapy in children

PURPOSE: To examine benzoporphyrin derivative angiography as a modality for studying photosensitizer biodistribution in experimental choroidal melanomas. METHODS: A liposomal preparation of benzoporphyrin derivative was used in this study. Digital benzoporphyrin derivative angiograms were performed in 10 rabbits (six for experimental choroidal melanomas, two for normal choroids, and two for irides) using a Topcon ImageNet H1024 digital imaging system, a Kodak Megaplus video camera, and a Topcon TRC-50-VT fundus camera. Only one eye from each rabbit was used. Filters specifically designed for benzoporphyrin derivative (peak absorption at 580 nm and peak emission at 695 nm) were used. Benzoporphyrin derivative (1 mg/kg) was injected into an ear vein while images of tumor, normal choroid, or iris were being obtained. Follow-up images were obtained during the first 3 hours and at 24 hours after injection. Fluorescence microscopy was performed in all 10 rabbits using 1 mg/kg of benzoporphyrin derivative. Tumor-bearing eyes were enucleated at the same time points that angiograms were performed, and the two sets of results were compared for maximum dye accumulation. RESULTS: Digital angiography demonstrated that maximal benzoporphyrin derivative fluorescence occurred in tumors 15 to 45 minutes after injection. Fluorescence photometry corroborated these results. CONCLUSION: Photosensitizer angiography is a valid modality for determining the optimum treatment time for photodynamic therapy.     

Matrix metalloproteinase expression in rat pancreatic islets

OBJECTIVE: To determine whether the type of prosthetic material and technique of placement influenced long-term complications after repair of incisional hernias. DESIGN: Retrospective cohort analytic study. SETTING: University-affiliated hospital. PATIENTS: Two hundred patients undergoing open repair of abdominal incisional hernias with prosthetic material between 1985 and 1994. INTERVENTIONS: Four types of prosthetic material were used and placed either as an onlay, underlay, sandwich, or finger interdigitation technique. The materials were monofilamented polypropylene mesh (Marlex, Davol Inc, Cranston, RI), double-filamented mesh (Prolene, Ethicon Inc, Somerville, NJ), expanded polytetrafluroethylene patch (Gore-Tex, WL Gore & Associates, Phoenix, Ariz) or multifilamented polyester mesh (Mersilene, Ethicon Inc). MAIN OUTCOME MEASURES: The incidence of recurrence and complications such as enterocutaneous fistula, bowel obstruction, and infection with each type of material and technique of repair were compared with univariate and multivariate analysis. RESULTS: On univariate analysis, multifilamented polyester mesh had a significantly higher mean number of complications per patient (4.7 vs 1.4-2.3; P<.002), a higher incidence of fistula formation (16% vs 0%-2%; P<.001), a greater number of infections (16% vs 0%-6%; P<.05), and more recurrent hernias (34% vs 10%-14%; P<.05) than the other materials used. The additional mean length of stay to treat complications was also significantly longer (30 vs 3-7 days; P<.001) when polyester mesh was used. The deleterious effect of polyester mesh on long-term complications was confirmed on multiple logistic regression (P=.002). The technique of placement had no influence on outcome. CONCLUSION: Polyester mesh should no longer be used for incisional hernia repair.     

Effect of mild acid treatment on the survival, enteropathogenicity, and protein production in vibrio parahaemolyticus

Vibrio parahaemolyticus is an important food-borne enteropathogen that encounters various adverse conditions in its native environment or during infection. Effects of mild acid treatment on survival under stress conditions, enteropathogenicity, and protein production in this pathogen were investigated. Logarithmically grown cells, at pH 7.5 shifted to pH 5.0 for 30 min, were more resistant to subsequent acid challenge at pH 4.4. A two-phase adaptive procedure (pH 5.8 for 30 min; pH 5.0 for 30 min) was better than a single-phase procedure for enhancing the acid tolerance of this pathogen. The acid-adapted cells were cross-protected against the challenges of low salinity and thermal inactivation. One-dimensional polyacrylamide gel electrophoresis revealed that proteins with molecular masses of 6.4, 9.0, 13.6, 16.3, 18.9, 22.9, 24.4, 28.3, 33. 9, 36.9, 41.2, 47.6, 58.1, 65.6, 80.5, 88.2, and 96.9 kDa were induced or significantly enhanced, while proteins of 25.3, 30.1, 30. 7, and 91.7 kDa were significantly inhibited. Two-dimensional polyacrylamide gel electrophoresis revealed that 20 species of proteins were induced or significantly enhanced, while 26 species were inhibited. In assays conducted using the suckling mouse model, enteropathogenicity of the acid-adapted cells was significantly enhanced in terms of intestine/body weight ratio and in vivo recovery of infected cells.     

Time is of the essence: a conjecture that hemispheric specialization arises from interhemispheric conduction delay

Tomasch (1954) and Aboitiz et al. (1992) found the majority of the fibers of the human corpus callosum are under 1 micron in diameter. Electron microscopic studies of Swadlow et al. (1980) and the detailed study of LaMantia and Rakic (1990a) on macaques show the average size of the myelinated callosal axons also to be less than 1 micron. In man, the average-sized myelinated fiber interconnecting the temporal lobes would have a one-way, interhemispheric delay of over 25 msec. Thus, finely detailed, time-critical neuronal computations (i.e., tasks that strain the capacity of the callosum and hence could not be handled by just the larger fibers) would be performed more quickly via shorter and faster intrahemispheric circuits. While one transit across the commissural system might yield tolerable delays, multiple passes as in a system involving "setting" would seem prohibitively slow. We suggest that these temporal limits will be avoided if the neural apparatus necessary to perform each high-resolution, time-critical task is gathered in one hemisphere. If the, presumably overlapping, neural assemblies needed to handle overlapping tasks are clustered together, this would lead to hemispheric specialization. The prediction follows that the large brains of mammals such as elephants and cetaceans will also manifest a high degree of hemispheric specialization.     

Therapeutic strategies in acute myocardial infarction. Results of STIM 93 registry

A registry was set up by the national college of cardiologists practicing in general hospitals in February 1993. The data concerned mode of admission, demographic details, initial clinical and haemodynamic evaluation and hospital outcome. Special attention was given to the electrocardiographic changes before and, in patients receiving thrombolytic therapy, after treatment. An analysis of predictive factors for mortality was performed both in the group of patients "revascularised" and in the group treated conventionally. One thousand and twenty three cases from 327 centres were analysed. There were 1292 men and 531 women, with an average age of 67.9 years. The average time interval from onset of symptoms to hospital admission was 5 h 30 min, 56.8% of patients arriving within 6 hours. 36.4% of the population underwent thrombolysis or angioplasty, 75% of patients under 75 years of age admitted before the 5th hours underwent a procedure of myocardial revascularisation. The hospital mortality was 14%, 8.7% in those revascularised and 17% in patients treated conventionally. Factors predictive of mortality were age, female gender, Killip Classes III or IV, systolic blood pressure of less than 100 mmHg, heart rate of more than 100/min and contraindications of thrombolysis. The maximum ST depression, the sum of ST depression, the sum of ST elevation and depression, were also significant predictive factors of a fatal hospital outcome in the whole population group and in patients treated conventionally. In the reperfused group, only the initial sum of ST elevation and depression was predictive of mortality: 120 minutes after the beginning of thrombolysis, the sum of ST elevations and of elevations and depressions was predictive of twice the mortality when the values exceeded 0.6 mv and 1.4 mv respectively.     

Method of imaging low density lipoproteins by atomic force microscopy

This short paper reports a simple method to image low density lipoproteins (LDL) using atomic force microscopy (AFM). This instrument allows imaging of biological samples in liquid and presents the advantage of needing no sample preparation such as staining or fixation that may affect their general structure. Dimensions (diameter and height) of individual LDL particles were successfully measured. AFM imaging revealed that LDL have a quasi-spherical structure on the x and y axis with an oblate spheroid structure in the z axis (i.e., height). LDLs were found to have an average diameter of 23 +/- 3 nm. The obtained mean height was 10 +/- 2 nm.