Perturbation theory for the effective diffusion constant in a medium of random scatterer

We develop perturbation theory and physically motivated resummations of the perturbation theory for the problem of a tracer particle diffusing in a random media. The random media contains point scatterers of density $\rho$ uniformly distributed through out the material. The tracer is a Langevin particle subjected to the quenched random force generated by the scatterers. Via our perturbative analysis we determine when the random potential can be approximated by a Gaussian random potential. We also develop a self-similar renormalisation group approach based on thinning out the scatterers, this scheme is similar to that used with success for diffusion in Gaussian random potentials and agrees with known exact results. To assess the accuracy of this approximation scheme its predictions are confronted with results obtained by numerical simulation.Comment: 22 pages, 6 figures, IOP (J. Phys. A. style

Modulation of oestrone sulphate formation and hydrolysis in breast cancer cells by breast cyst fluid from British and Hungarian women

Women with gross cystic breast disease may have an increased risk of breast cancer. In this study the ability of breast cyst fluid (BCF), obtained from British or Hungarian women, to modulate oestrone sulphate (E1S) formation or hydrolysis, has been examined. For this, oestrogen receptor-positive (ER+) MCF-7 or MDA-MB-231 (ER–) breast cancer cells were employed. The formation and hydrolysis of E1S was measured using radiometric techniques. BCF from British and Hungarian women mainly inhibited E1S hydrolysis in MCF-7 cells while stimulating hydrolysis in MDA-MB-231 cells. The extent of inhibition or stimulation of E1S hydrolysis in these cells was related to the Na+/K+ratio of the BCF. There was a significant inverse relationship between the extent to which BCF samples inhibited hydrolysis in MCF-7 cells and stimulated it in MDA-MB-231 cells. BCF stimulated E1S formation in MCF-7 cells while inhibiting formation in MDA-MB-231 cells. No difference in the ability of BCF from British or Hungarian women to inhibit or stimulate E1S hydrolysis was detected in ER+ or ER– breast cancer cells. In contrast, BCF from British women stimulated E1S formation in ER+ cells (median 82%) to a significantly greater extent (P< 0.01) than BCF from Hungarian women (median 33%). The role that E1S has in breast cancer development remains unclear. The greater stimulation of E1S formation by BCF from British women, who have a higher risk of breast cancer than Hungarian women, suggests that it may act as a storage form of oestrogen within cells that can be activated by oestrone sulphatase. © 2000 Cancer Research Campaig

Differential effect of cholera toxin on CD45RA+ and CD45RO+ T cells: specific inhibition of cytokine production but not proliferation of human naive T cells

We have studied how cholera toxin (CT) and its non-toxic cell-binding B-subunit (CTB) affect the activation of pure human T cells in an anti-CD3-driven system. CT, as opposed to CTB, strongly suppressed the proliferative responses as well as cytokine production in CD4+ and CD8+ T cells. CT however, had a differential effect on naive and activated/memory T cell subsets. Costimulation through exogenous IL-2 or through CD28 cross-linking rescued the proliferation of CT-treated naive CD45RA+ T cells, but not of activated/memory CD45RO+ cells. IL-2 production and IL-2 receptor expression were markedly reduced by CT in all T cell fractions, i.e. also in CD45RA+ cells which had maintained proliferative responses. However, the proliferative responses of CT-treated CD45RA+ T cells were IL-2-dependent, as shown by blocking experiments using anti-IL-2 antibodies. These results indicate (i) that CTB has no cytostatic effect on human T cells, (ii) that CT affects proliferation and cytokine production by two different signal pathways, and (iii) that CT might interact with a signal pathway generated through or influenced by CD45