P2 receptors mediate the actions of the extracellular nucleotides ATP, ADP, UTP, and UDP, regulating several physiologic responses including cardiac function, vascular tone, smooth muscle cell (SMC) proliferation, platelet aggregation, and the release of endothelial factors. P2 receptor characterization has been hampered by the lack of selective antagonists. The aim of the current study was to investigate the mRNA and protein expression of P2X and P2Y receptors in human SMC and in endothelial cells (EC). Smooth muscle cells were obtained from human mammary artery and EC from human umbilical vein. Using real-time PCR, the authors established quantitative mRNA assays. Protein expression was studied using Western blotting with recently developed antibodies. The P2X1 receptor was highly specific for human SMC, while the P2X4 was the highest expressed receptor in EC. The P2Y2 receptor was present in both SMC and EC. UTP-mediated effects in these cells are likely to be mediated by P2Y2 and not P2Y4 receptors since the latter had considerably lower expression. The P2Y6 receptor was expressed in both SMC and EC. The P2Y1 and surprisingly the P2Y11 receptors were the most abundantly expressed P2Y receptors in the endothelium. Overall, Western blotting confirmed the mRNA findings in most aspects, and most interestingly, indicated oligomerization of the P2Y1 receptor that may be important for its function. In conclusion, P2X1, P2Y2, and P2Y6 are the most expressed P2 receptors in SMC and are thus probably mediating the contractile and mitogenic actions of extracellular nucleotides. The P2X4, P2Y11, P2Y1, and P2Y2 are the most expressed P2 receptors in EC, and are most likely mediating release of nitric oxide, endothelium-dependent hyperpolarizing factor (EDHF), and t-PA induced by extracellular nucleotides. These findings will help to direct future cardiovascular drug development against the large P2 receptor family.

Mercury in the Arctic is an important environmental and human health issue. The reliance of Northern Peoples on traditional foods, such as marine mammals, for subsistence means that they are particularly at risk from mercury exposure. The cycling of mercury in Arctic marine systems is reviewed here, with emphasis placed on the key sources, pathways and processes which regulate mercury levels in marine food webs and ultimately the exposure of human populations to this contaminant. While many knowledge gaps exist limiting our ability to make strong conclusions, it appears that the long range transport of mercury from Asian emissions is an important source of atmospheric Hg to the Arctic and that mercury methylation resulting in monomethylmercury production (an organic form of mercury which is both toxic and bioaccumulated) in Arctic marine waters is the principal source of mercury incorporated into food webs. Mercury concentrations in biological organisms have increased since the onset of the industrial age and are controlled by a combination of abiotic factors (e.g., monomethylmercury supply), food web dynamics and structure, and animal behavior (e.g., habitat selection and feeding behavior). Finally, although some Northern Peoples have high mercury concentrations of mercury in their blood and hair, harvesting and consuming traditional foods has many nutritional, social, cultural and physical health benefits which must be considered in risk management and communication.

No abstract

We have used an extraction procedure, which released membrane-bound apoB-100, to study the assembly of apoB-48 VLDL (very low density lipoproteins). This procedure released apoB-48, but not integral membrane proteins, from microsomes of McA-RH7777 cells. Upon gradient ultracentrifugation, the extracted apoB-48 migrated in the same position as the dense apoB-48-containing lipoprotein (apoB-48 HDL (high density lipoprotein)) secreted into the medium. Labeling studies with [ 3 H]glycerol demonstrated that the HDL-like particle extracted from the microsomes contains both triglycerides and phosphatidylcholine. The estimated molar ratio between triglyceride and phosphatidylcholine was 0.70 ؎ 0.09, supporting the possibility that the particle has a neutral lipid core. Pulse-chase experiments indicated that microsomal apoB-48 HDL can either be secreted as apoB-48 HDL or converted to apoB-48 VLDL. These results support the two-step model of VLDL assembly. To determine the size of apoB required to assemble HDL and VLDL, we produced apoB polypeptides of various lengths and followed their ability to assemble VLDL. Small amounts of apoB-40 were associated with VLDL, but most of the nascent chains associated with VLDL ranged from apoB-48 to apoB-100. Thus, efficient VLDL assembly requires apoB chains of at least apoB-48 size. Nascent polypeptides as small as apoB-20 were associated with particles in the HDL density range. Thus, the structural requirements of apoB to form HDL-like first-step particles differ from those to form second-step VLDL. Analysis of proteins in the d < 1.006 g/ml fraction after ultracentrifugation of the luminal content of the cells identified five chaperone proteins: binding protein, protein disulfide isomerase, calcium-binding protein 2, calreticulin, and glucose regulatory protein 94. Thus, intracellular VLDL is associated with a network of chaperones involved in protein folding. Pulse-chase and subcellular fractionation studies showed that apoB-48 VLDL did not accumulate in the rough endoplasmic reticulum. This finding indicates either that the two steps of apoB lipoprotein assembly occur in different compartment or that the assembled VLDL is transferred rapidly out of the rough endoplasmic reticulum.

) over the NA (steeper than at Northern Hemispheric land sites) but no significant decline over the SA. Surface water Hg 0 measurements in the NA show a decline of À5.7% a À1 since 1999, and limited subsurface ocean data show an $80% decline from 1980 to present. We use a coupled global atmosphere-ocean model to show that the decline in NA atmospheric concentrations can be explained by decreasing oceanic evasion from the NA driven by declining subsurface water Hg concentrations. We speculate that this large historical decline of Hg in the NA Ocean could have been caused by decreasing Hg inputs from rivers and wastewater and by changes in the oxidant chemistry of the atmospheric marine boundary layer.