Metabolism of cationized lipoproteins by human fibroblasts: biochemical and morphologic correlations

Human plasma low density lipoprotein (LDL) that had been rendered polycationic by coupling with N, N-dimethyl-1, 3-propanediamine (DMPA) was shown by electron microscopy to bind in clusters to the surface of human fibroblasts. The clusters resembled those formed by polycationic ferritin (DMPA-feritin), a visual probe that binds to anionic site on the plasma membrane. Biochemical studies with (125)I-labeled DMPA-LDL showed that the membrane-bound lipoprotein was internalized and hydrolyzed in lysosomes. The turnover time for cell bound (125)I-DMPA-LDL, i.e., the time in which the amount of (125)I-DMPA-LDL degraded was equal to the steady-state cellular content of the lipoprotein, was about 50 h. Because the DMPA-LDL gained access to fibroblasts by binding nonspecifically to anionic sites on the cell surface rather than by binding to the physiologic LDL receptor, its uptake failed to be regulated under conditions in which the uptake of native LDL was reduced by feedback suppression of the LDL receptor. As a result, unlike the case with native LDL, the DMPA-LDL accumulated progressively within the cell, and this led to a massive increase in the cellular content of both free and esterified cholesterol. Studies with (14)C-oleate showed that at least 20 percent of the accumulated cholesteryl esters represented cholesterol that had been esterified within the cell. After 4 days of incubation with 10 μg/ml of DMPA-LDL, fibroblasts had accumulated so much cholesteryl ester that neutral lipid droplets were visible at the light microscope level with Oil Red O staining. By electron microscopy, these intracellular lipid droplets were observed to lack a tripartite limiting membrane. The ability to cause the overaccumulation of cholesteryl esters within cells by using DMPA-LDL provides a model system for study of the pathologic consequences at the cellular level of massive deposition of cholesteryl ester.     

Marking as a decision factor in the choice of a new resting site in <Emphasis Type="Italic">Lasius niger</Emphasis>

Summary In ants, aggregation is mainly based on the attraction between individuals. We confirmed the existence of ground marking in Lasius niger and demonstrated its influence on the aggregative behaviour of ants: the place of the gathering is leading by the existence of a ground marking which favours clustering by increasing the rate of the process but does not change the aggregation level. This factor could play a role in the choice of a new nest site and in the spatial distribution of ants inside the nest. This marking, presuming to have a long duration, could represent an external memory which could play an important role in various situations such as the choice of new nest or the reorganisation of ants after a disturbance.Received 23 July 2003; revised 16 December 2003; accepted 19 December 2003.     

Can individual heterogeneity influence self-organised patterns in the termite nest construction model?

We present investigations on the influence of individual heterogeneity on self-organised patterns in the termite nest construction model. The presented results extend the original model (Bruinsma 1979; Deneubourg 1977) from theoretical biology which has served as foundation and inspiration for computational optimisation approaches. Our findings have implications for the handling of heterogeneities inherent to physical sensing devices as well as indicate the potential of intentionally endowing software agents or their hardware embodiments (robots, sensor nodes, etc.) with a degree of individuality. We show that increasing heterogeneity is equivalent to changing the values of certain global parameters.