The role of parathyroid hormone and calcitonin in magnesium absorption in the rat small intestine

Summary We studied duodenal and ileal magnesium (Mg) absorption in intact, parathyroidectomized (PTX), thyroid-(TX) and thyroparathyroidectomized (TPTX) rats with iodine hormones replaced, and, additionally, in PTX rats receiving bovine parathyroid hormone 1–34 and 1,25-dihydroxyvitamin D₃, respectively. Ma absorption was reduced after PTX and TPTX in the duodenum, but not in the ileum, whereas TX had no influence on duodenal or ileal Mg absorption. Both bovine parathyroid hormone 1–34 and 1,25-dihydroxyvitamin D₃ increased Mg absorption in the duodenum and the ileum in PTX rats.Acknowledgments. We are grateful to B. Schreiber, K. Schwille and I. Goldberg for technical and secretarial help. Supported by Deutsche Forschungsgemeinschaft (Schw 210/3). Reprint requests to P.O.S., University Hospital, Maximiliansplatz, D-8520 Erlangen.     

Submucosal glands are the predominant site of CFTR expression in the human bronchus.

We have used in situ hybridization and immunocytochemistry to characterize the cellular distribution of cystic fibrosis (CF) gene expression in human bronchus. The cystic fibrosis transmembrane conductance regular (CFTR) was primarily localized to cells of submucosal glands in bronchial tissues from non-CF individuals notably in the serous component of the secretory tubules as well as a subpopulation of cells in ducts. Normal distribution of CFTR mRNA was found in CF tissues while expression of CFTR protein was genotype specific, with delta F508 homozygotes demonstrating no detectable protein and compound heterozygotes expressing decreased levels of normally distributed protein. Our data suggest mechanisms whereby defects in CFTR expression could lead to abnormal production of mucus in human lung.     

A mechanosensory complex that mediates the endothelial cell response to fluid shear stress

Shear stress is a fundamental determinant of vascular homeostasis, regulating vascular remodelling, cardiac development and atherogenesis, but the mechanisms of transduction are poorly understood. Previous work showed that the conversion of integrins to a high-affinity state mediates a subset of shear responses, including cell alignment and gene expression. Here we investigate the pathway upstream of integrin activation. PECAM-1 (which directly transmits mechanical force), vascular endothelial cell cadherin (which functions as an adaptor) and VEGFR2 (which activates phosphatidylinositol-3-OH kinase) comprise a mechanosensory complex. Together, these receptors are sufficient to confer responsiveness to flow in heterologous cells. In support of the relevance of this pathway in vivo, PECAM-1-knockout mice do not activate NF-kappaB and downstream inflammatory genes in regions of disturbed flow. Therefore, this mechanosensing pathway is required for the earliest-known events in atherogenesis.     

Effects of macrophyte species richness on wetland ecosystem functioning and services

Wetlands provide many important ecosystem services to human society, which may depend on how plant diversity influences biomass production and nutrient retention. Vascular aquatic plant diversity may not necessarily enhance wetland ecosystem functioning, however, because competition among these plant species can be strong, often resulting in the local dominance of a single species. Here we have manipulated the species richness of rooted, submerged aquatic plant (macrophyte) communities in experimental wetland mesocosms. We found higher algal and total plant (algal plus macrophyte) biomass, as well as lower loss of total phosphorus, in mesocosms with a greater richness of macrophyte species. Greater plant biomass resulted from a sampling effect; that is, the increased chance in species mixtures that algal production would be facilitated by the presence of a less competitive species-in this case, crisped pondweed. Lower losses of total phosphorus resulted from the greater chance in species mixtures of a high algal biomass and the presence of sago pondweed, which physically filter particulate phosphorus from the water. These indirect and direct effects of macrophyte species richness on algal production, total plant biomass and phosphorus loss suggest that management practices that maintain macrophyte diversity may enhance the functioning and associated services of wetland ecosystems.     

一种新型高价锰取代的多金属氧酸盐合成、结构及性质研究

在含有MnⅡ的夹心型多金属氧酸盐水溶液中加入强氧化剂KMnO4,制得一种新型的含有MnⅢ的多金属氧酸盐K5Na3[{MnⅢ(H2O)}2(WO)(H2O) (AsW9O33)2]·18H2O (KNa-1).该化合物的多阴离子结构是基于2个B-α-[AsW9]三缺位Keggin型构筑单元,中间夹着2个{MnⅢ(H2O)}和1个{WⅥO}片段而构成的夹心式构型.对KNa-1进行了变温磁化率测定并采用双核MnⅢ簇为模型进行了拟合,并对该化合物进行了电化学分析.结果表明:KNa-1 中的2个MnⅢ中心存在弱的反铁磁相互作用;化合物中的MnⅢ离子具有不可逆的氧化还原过程.     

Switch of flow direction in an Antarctic ice stream

Fast-flowing ice streams transport ice from the interior of West Antarctica to the ocean, and fluctuations in their activity control the mass balance of the ice sheet. The mass balance of the Ross Sea sector of the West Antarctic ice sheet is now positive--that is, it is growing--mainly because one of the ice streams (ice stream C) slowed down about 150 years ago. Here we present evidence from both surface measurements and remote sensing that demonstrates the highly dynamic nature of the Ross drainage system. We show that the flow in an area that once discharged into ice stream C has changed direction, now draining into the Whillans ice stream (formerly ice stream B). This switch in flow direction is a result of continuing thinning of the Whillans ice stream and recent thickening of ice stream C. Further abrupt reorganization of the activity and configuration of the ice streams over short timescales is to be expected in the future as the surface topography of the ice sheet responds to the combined effects of internal dynamics and long-term climate change. We suggest that caution is needed when using observations of short-term mass changes to draw conclusions about the large-scale mass balance of the ice sheet.