Platelet active concentration profiles near growing thrombi. A mathematical consideration.

When blood contacts foreign material surfaces, platelets usually adhere and form aggregates on those surfaces, generating mural thrombi. The mechanism of mural thrombogenesis is not completely understood, but one hypothesis states that the local release of certain platelet-active substances from the platelets composing an initial small thrombus stimulates additional platelet recruitment to that thrombus, resulting in growth of the cell aggregate. The purpose of this paper is to investigate the feasibility of this hypothesis. Concentration profiles of adenosine diphosphate (ADP), thromboxane A2 (TxA2), and thrombin were computed in the vicinity of growing model thrombi 10 and 20 micron long. Wall shear rates of 100, 500, and 1,500 s-1 were considered for blood flowing through a thin rectangular slit 200 micron wide coated with collagen, a predominant subendothelial protein. The local concentrations of ADP and TxA2 were marginally large enough to stimulate platelet activation individually, while local thrombin levels can be much greater than required for stimulation. Antithrombin III, a natural thrombin inhibitor, did not significantly reduce the thrombin concentrations, but antithrombin III accelerated by heparin greatly reduced the local thrombin concentrations. The reduced thrombin levels may, however, still be large enough to activate platelets.     

Mechanical effects on endothelial cell morphology: In vitro assessment

Summary Endothelial cells are subjected to fluid mechanical forces which accompany blood flow. These cells become elongated and orient their long axes parallel to the direction of shear stress when the cultured cells are subjected to flow in an in vitro circulatory system. When the substrate is compliant and cyclically deformed, to simulate effects of pressure in the vasculature, the cells elongate an orient perpendicular to the axis of deformation. Cell shape changes are reflected in the alignment of microtubule networks. The systems described provide tools for assessing the individual roles of shear stress, pressure, and mechanical strain on vascular cell structure and function. This work was partially supported by grants HL 17437, HL 18072, and HL 23016 from the National Institutes of Health, Bethesda, MD, and grant C-938 from the Robert A. Welch Foundation.     

The finO gene of antibiotic resistance plasmid R100

Lambda phages carrying the R100 finO gene have been isolated from an R100:: lambda cointegrate in which lambda was inserted into the R100 traD gene at kb coordinate 72.1. Physical analyses of these phages place the finO gene within R100 SalI fragment D, near kb coordinate 82.0. Analysis of proteins synthesized by the phages did not identify the finO gene product, although a constitutive protein of m.w. 30,100 was encoded by R100 DNA between kb coordinates 78.7 and 81.2.     

Transfer-deficient cointegrates of Flac and lambda prophage

Summary Twelve transfer-deficient mutants of the plasmid Flac were obtained by insertion of prophage lambda into secondary attachment sites within the transfer region. Insertions into eight different tra genes were identified. These mutations were strongly polar on expression of tra genes previously mapped downstream, and thus confirmed that the genes traA through traD form a single operon. However, some continued expression of traI suggested that this was transcribed in part from a promoter located between traD and tral, and in part from the transfer operon promoter. One insertion early in the transfer operon produced a plasmid-specific tra mutation not complemented by R100-1 or R1-19: this insertion was into a new gene (traY), located before traA as the first member of the transfer operon. Partial tra deletion mutants were obtained as 42° C — survivors from several of the Flac tra:: ED4 plasmids, and their properties are described.     

Treatment of metal-contaminated water using bacterial sulfate reduction: results from pilot-scale reactors

Simple anaerobic reactors were installed to treat metal-contaminated water in an underground coal mine and at a smelting residues dump in Pennsylvania. The reactors consisted of barrels and tanks filled with spent mushroom compost, within which bacterial sulfate reduction became established. Concentrations of Al, Cd, Fe, Mn, Ni, and Zn were typically lowered by over 95% as contaminated water flowed through the reactors. Cadmium, Fe, Ni, and some Zn were retained as insoluble metal sulfides following their reaction with bacterially generated H(2)S. Aluminum, Mn, and some Zn hydrolyzed and were retained as insoluble hydroxides or carbonates. Reactor effluents were typically circumneutral in pH and contained net alkalinity. The principal sources of alkalinity in the reactors were bacterial sulfate reduction and limestone dissolution. This article examines the chemistry of the reactor systems and the opportunities for enhancing their metal-retaining and alkalinity-generating potential. (c) 1992 John Wiley & Sons, Inc.     

Lucky rugose corals on crinoid stems: unusual examples of subepidermal epizoans from the Devonian of Morocco

Berkowski, B & Klug, C. 2011: Lucky rugose corals on crinoid stems: unusual examples of subepidermal epizoans from the Devonian of Morocco. Lethaia, Vol. 45, pp. 24–33. In the fossil record, evidence for true epizoans, i.e. living animals inhabiting other living host‐animals, is rather rare. A host reaction is usually needed to proof the syn vivo‐settling of the epizoan. Herein, we provide a first report of such an epizoan biocoenosis from various strata of the Early Devonian of Hamar Laghdad, the world‐renowned Moroccan mud‐mound locality. In this case, solitary rugose corals settled as larvae on crinoid stems, perhaps at a spot where the epidermis was missing for some reason (injury, disease). Both the crinoid and the coral began to grow around each other. By doing so, the affected crinoid columnals formed a swelling, where ultimately only an opening slightly larger than the coral orifice remained. We discuss both macroecological and small‐scale synecological aspects of this biocoenosis. The coral profited from its elevated home because it reached into more rapid currents providing the polyp with more food than at the densely populated seafloor, which was probably covered by a coral‐meadow around the mounds and hydrothermal vents. □Corals, crinoids, Early Devonian, epizoans, Morocco, Rugosa.     

Shear sensitivity of hybridoma cells in batch, fed-batch, and continuous cultures.

Previously, we observed that CRL-8018 hybridoma cells were more sensitive to well-defined viscometric shear during the lag and stationary phases than during the exponential phase of batch cultures. Some potential hypotheses for explaining the increase in shear sensitivity are (1) nutrient limitations that result in a decrease in production of specific cellular components responsible for the mechanical strength of the cell, (2) nutrient limitations that lead to synchronization of the culture in a cell cycle phase that is more sensitive to shear, or (3) a link between cell growth and shear sensitivity, such that slowly growing cells are more sensitive to shear. Here, the duration of the exponential phase was increased with use of fed-batch, and the effect on shear sensitivity of the cultures was measured with a viscometric technique. Extension of exponential growth resulted in an increased period during which the cells were insensitive to shear. Additionally, the shear sensitivity of the cells was constant over a wide range of growth rates and metabolic yields in chemostat cultures. These observations suggest that as long as the cells are actively (exponentially) growing, their shear sensitivity does not depend on the growth rate or metabolic state of the cell as expressed by metabolic yields. Thus, hypothesis 3 above can be dismissed.     

Meta-analysis of the literature on diagnostic accuracy of SPECT in parkinsonian syndromes

Background  

Parkinson's disease (PD) is the second most common neurodegenerative disorder. One of the most widely used techniques to diagnose PD is a Single Photon Emission Computer Tomography (SPECT) scan to visualise the integrity of the dopaminergic pathways in the brain. Despite this there remains some discussion on the value of SPECT in the differential diagnosis of PD. We did a meta-analysis of all the existing literature on the diagnostic accuracy of both pre- and post-synaptic SPECT imaging in the differential diagnosis of PD.