Pinning and depinning of the polarization of exciton-polariton condensates at room temperature.

A room temperature polariton condensate realized in a microcavity with embedded GaN quantum wells emits linearly polarized light at threshold with the plane of polarization pinned to one of the crystallographic axes. With increasing pumping power, a depinning of the polarization is observed resulting in a progressive decrease of the polarization degree of the emitted light. This depinning is understood in terms of polariton-polariton repulsion competing with the static disorder potential effect. The polarization behavior differs from that of conventional lasers where the polarization degree usually increases as a function of pumping power.

Enhanced membrane phospholipid metabolism in human pancreatic adenocarcinoma cell lines detected by low-resolution 1H nuclear magnetic resonance spectroscopy.

The low-resolution proton nuclear magnetic resonance (NMR) spectra of human pancreatic adenocarcinomas maintained in nude mice and in culture exhibit characteristic features. First, the high values of longitudinal (T1) and transverse (T2) relaxation times were attributed to disturbances in the exchange of ions and water molecules in cancerous cells. Second, a new peak situated at about 1.8 +/- 0.2 ppm from the peak of tissular water was observed. It was higher in spectra recorded from the proliferative peripheral zone of the tumor than from the central necrotic zone and was not observed in healthy control pancreatic tissue. Histological examination of the xenografts by transmission electron microscopy indicated intense phospholipid metabolism with marked development of the plasma membrane and the presence of numerous secretory granules, lysosomes, and multivesicular bodies in the cytoplasm. The new 1H NMR low-resolution peak was thought to reflect an increase in membrane viscosity stemming from alterations in the structure and metabolism of membrane phospholipids. Whatever its origin, the 1.8-ppm peak is a particular feature of cancerous pancreatic cells, which should be readily detectable by NMR in vivo.

Differentiation of the human pancreatic adenocarcinoma cell line (Capan-1) in culture and co-culture with fibroblasts dome formation.

This study was designed to investigate differentiation of human pancreatic duct carcinoma cells (Capan-1) in vitro. Observations on live cells, and electron microscopic examination, together with enzymological and immunocytochemical methods, have demonstrated that these cells differentiate spontaneously at an early stage. The cells are seen to be joined by apical junctions. High ATPase activity can be detected in the basolateral membranes, and the cells secrete a gastric type mucin (MI) bearing acidic groups. During differentiation in culture, they form domes which are thought to be the morphological expression of trans-epithelial transport of water and electrolytes. This particular structure is transitory, since after 6 days in culture all the cells lose their adhesivity, and form into floating cords. Co-culture of Capan-1 cells and human, nude mice or chick embryo fibroblasts leads to a higher degree of differentiation of epithelial cells, reflected by the earlier appearance of numerous domes. In addition, the anchorage of Capan-1 cells to fibroblasts prevents retraction of the monolayer, and enables the domes to be maintained in the cultures for more than one month. These findings suggest that Capan-1 cells are able to carry out trans-epithelial movement of water and electrolytes. It is suggested that excretion of ions (bicarbonate and/or chloride) is preserved after transformation of pancreatic duct cells. Mucins (MI) and the recently described VIP receptor sites are also thought to play a part in these exchange processes.