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51.
O Christensen 《Nature》1987,330(6143):66-68
Animal cells initially swell in hypotonic media by osmotic water equilibration, but their volume is subsequently regulated by a net loss of KCl and amino acids with concomitant loss of cell water. Mechanisms for regulating cell volume are important in allowing cells to adapt to variations in external tonicity and metabolic load. In red cells the KCl loss is mediated by electroneutral ion transport mechanisms. In contrast, conductive K+ and Cl- transport pathways are activated during regulatory volume decrease in several cell types including epithelia. The activation seems to be mediated by internal Ca2+, but the detailed mechanism is not known. In a leaky epithelium, the choroid plexus epithelium, we have found a cation-selective, Ca2+-permeable channel which opens with membrane stretch. The epithelium also contains a high density of the large (approximately 200 pS) type of Ca2+- voltage-activated K+ channel. Both channels are normally closed. I propose that in hypotonic media, the stretching of the cell membrane produced by the initial swelling causes influx of Ca2+ through the stretch-activated channels, which activates the neighbouring large K+ channels to produce increased K+ outflux with associated loss of cell water. 相似文献
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53.
Mutations in AXIN2 cause colorectal cancer with defective mismatch repair by activating beta-catenin/TCF signalling 总被引:12,自引:0,他引:12
54.
New high-pressure phases of lithium 总被引:3,自引:0,他引:3
Lithium is considered a 'simple' metal because, under ordinary conditions of pressure and temperature, the motion of conduction electrons is only weakly perturbed by interactions with the cubic lattice of atomic cores. It was recently predicted that at pressures below 100 GPa, dense Li may undergo several structural transitions, possibly leading to a 'paired-atom' phase with low symmetry and near-insulating properties. Here we report synchrotron X-ray diffraction measurements that confirm that Li undergoes pronounced structural changes under pressure. Near 39 GPa, the element transforms from a high-pressure face-centred-cubic phase, through an intermediate rhombohedral modification, to a cubic polymorph with 16 atoms per unit cell. This cubic phase has not been observed previously in any element; unusually, its calculated electronic density of states exhibits a pronounced semimetal-like minimum near the Fermi energy. We present total-energy calculations that provide theoretical support for the observed phase transition sequence. Our calculations indicate a large stability range of the 16-atom cubic phase relative to various other crystal structures tested here. 相似文献
55.
UTX and JMJD3 are histone H3K27 demethylases involved in HOX gene regulation and development 总被引:2,自引:0,他引:2
Agger K Cloos PA Christensen J Pasini D Rose S Rappsilber J Issaeva I Canaani E Salcini AE Helin K 《Nature》2007,449(7163):731-734