Effect of skin temperature on the ion reabsorption capacity of sweat glands during exercise in humans.

The effect of skin temperature on the ion reabsorption capacity of sweat glands during exercise in humans is unknown. In this study, eight healthy subjects performed a 60-min cycling exercise at a constant intensity (60% VO(2max)) under moderate (25 degrees C) and cool (15 degrees C) ambient temperatures at a constant relative humidity of 40%. The sweating rate (SR), index of sweat ion concentration (ISIC) by using sweat conductivity, esophageal temperature (Tes), mean skin temperature, and heart rate (HR) were measured continuously under both ambient temperatures. The SR and ISIC were significantly lower at the cool ambient temperature versus the moderate temperature. There were no significant differences in the changes in HR and esophageal temperature between these ambient temperature conditions, while the mean skin temperature was significantly lower at the cool ambient temperature by almost 3 degrees C (P < 0.05). The slopes of the relationships between Tes and the SR and ISIC were significantly lower and the thresholds of these relationships were significantly higher at the cool ambient temperature (P < 0.05). The ion reabsorption capacity of the sweat glands was significantly lower (P < 0.05) in a cool environment (0.21 +/- 0.04 vs. 0.52 +/- 0.06 mg/cm(2)/min at 15 and 25 degrees C, respectively) as evaluated using the relationships for SR and ISIC. The results suggest that the ion reabsorption capacity of the sweat glands is influenced by skin temperature during exercise in humans.

A unique heparin-binding domain in the envelope protein of the neuropathogenic PVC-211 murine leukemia virus may contribute to its brain capillary endothelial cell tropism.

Previous studies from our laboratory demonstrated that PVC-211 murine leukemia virus (MuLV), a neuropathogenic variant of Friend MuLV (F-MuLV), had undergone genetic changes which allowed it to efficiently infect rat brain capillary endothelial cells (BCEC) in vivo and in vitro. Two amino acid changes from F-MuLV in the putative receptor binding domain (RBD) of the envelope surface protein of PVC-211 MuLV (Glu-116 to Gly and Glu-129 to Lys) were shown to be sufficient for conferring BCEC tropism on PVC-211 MuLV. Recent examination of the unique RBD of PVC-211 MuLV revealed that the substitution of Lys for Glu at position 129 created a new heparin-binding domain that overlapped a heparin-binding domain common to ecotropic MuLVs. In this study we used heparin-Sepharose columns to demonstrate that PVC-211 MuLV, but not F-MuLV, can bind efficiently to heparin and that one or both of the amino acids in the RBD of PVC-211 MuLV that are associated with BCEC tropism are responsible. We further showed that heparin can enhance or inhibit MuLV infection and that the mode of action is dependent on heparin concentration, sulfation of heparin, and the affinity of the virus for heparin. Our results suggest that the amino acid changes that occurred in the envelope surface protein of PVC-211 MuLV may allow the virus to bind strongly to the surface of BCEC via heparin-like molecules, increasing the probability that the virus will bind to its cell surface receptor and efficiently infect these cells.

Molecular characterization of the mouse Tem1/endosialin gene regulated by cell density in vitro and expressed in normal tissues in vivo.

Human tumor endothelial marker 1/endosialin (TEM1/endosialin) was recently identified as a novel tumor endothelial cell surface marker potentially involved in angiogenesis, although no specific function for this novel gene has been assigned so far. It was reported to be expressed in tumor endothelium but not in normal endothelium with the exception of perhaps the corpus luteum. Here we describe the cDNA and genomic sequences for the mouse Tem1/endosialin homolog, the identification and characterization of its promoter region, and an extensive characterization of its expression pattern in murine and human tissues and murine cell lines in vitro. The single copy gene that was mapped to chromosome 19 is intronless and encodes a 92-kDa protein that has 77.5% overall homology to the human protein. The remarkable findings are 1) this gene is ubiquitously expressed in normal human and mouse somatic tissues and during development, and 2) its expression at the mRNA level is density-dependent and up-regulated in serum-starved cells. In vitro, its expression is limited to cells of embryonic, endothelial, and preadipocyte origin, suggesting that the wide distribution of its expression in vivo is due to the presence of vascular endothelial cells in all the tissues. The ubiquitous expression in vivo is in contrast to previously reported expression limited to corpus luteum and highly angiogenic tissues such as tumors and wound tissue.