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There is increasing evidence that mammalian urinary tract epithelial cells utilize membrane channels and transporters to transport solutes across their apical (luminal) and basalateral membranes to modify solute concentrations in both cell and urine. This study investigates the expression, localization, and regulation of the ROMK ([K.sub.ir] 1.1) potassium channels in rat and dog ureter and bladder tissues. Immunoblots of homogenates of whole ureter, whole bladder, bladder epithelial cells, and bladder smooth muscle tissues in both rat and dog identified ~45- to 50-kDa bands characteristic of ROMK in all tissues. RT-PCR identified ROMK mRNA in these same tissues in both animal species. ROMK protein localized by immunocytochemistry was strongly expressed in the apical membranes of the large umbrella cells lining the bladder lumen and to a lesser extent in the cytoplasm of epithelial cells and smooth muscle cells in the rat bladder. ROMK protein and mRNA were also discovered in cardiac, striated, and smooth muscle in diverse organs. There was no difference in immunoblot expression of ROMK abundance in bladder homogenates (whole bladder, epithelial cell, or muscle cell) or ureteral homogenates between groups of rats fed high- or low-potassium diets. Although the functional role of ROMK in urinary tract epithelia and smooth muscle is unknown, ROMK may participate in the regulation of epithelial and smooth muscle cell volume and osmolality, in the dissipation of potassium leaked or diffused from urine across the epithelial cell apical membranes or tight junctions, and in net or bidirectional potassium transport across urinary tract epithelia. epithelial sodium channel; calponin

Double-strand breaks activate the ataxia telangiectasia mutated (ATM) kinase, which promotes the accumulation of DNA damage factors in the chromatin surrounding the break. The functional significance of the resulting DNA [...]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.cell.2008.03.004 Byline: R. Ileng Kumaran (1), Rajika Thakar (1), David L. Spector (1) Abstract: The mammalian cell nucleus provides a landscape where genes are regulated through their organization and association with freely diffusing proteins and nuclear domains. In many cases, specific genes are highly dynamic, and the principles governing their movements and interchromosomal interactions are currently under intensive study. Recent investigations have implicated actin and myosin in chromatin dynamics and gene expression. Here, we discuss our current understanding of the dynamics of the interphase genome and how it impacts nuclear organization and gene activity. Author Affiliation: (1) Cold Spring Harbor Laboratory, One Bungtown Road, Cold Spring Harbor, NY 11724, USA

Although the mammalian urinary tract is generally held to be solely a transit and storage vehicle for urine made by the kidney, in vivo data suggest reabsorption of urea and other urine constituents across urinary tract epithelia. To determine whether urinary tract tissue concentrations are increased as a result of such reabsorption, we measured urea nitrogen and creatinine concentrations and determined whether urea transporter B (UT-B) was present in bladder, ureter, and other tissues from dogs and rats. Mean urea nitrogen and creatinine concentrations in dogs and rats were three- to sevenfold higher in urinary tract tissues than in serum and were comparable to those in renal cortex. In waterrestricted or water-loaded rats, urea nitrogen concentrations in bladder tissues fell inversely with the state of hydration, were proportional to urine urea nitrogen concentrations, and were greater than the corresponding serum urea nitrogen concentration in every animal. Immunoblots of rat and dog urinary tract tissues demonstrated the presence of UT-B in homogenates of bladder and ureter, and immunocytochemical analysis localized UT-B to epithelial cell membranes. These findings are consistent with the notion that urea and creatinine are continuously reabsorbed from the urine across the urothelium, urea in part via UT-B, and that urine is thus altered in its passage through the urinary tract. Urea reabsorption across urinary tract epithelia may be important during conditions requiring nitrogen conservation and may contribute to pathophysiological states characterized by high blood urea nitrogen, such as prerenal azotemia and obstructive uropathy. urothelial transport; bladder; ureter

A report reveals that PIAS1 confers DNA-binding specificity on the Msx1homeoprotein by regulating its subnuclear localization and proximity to target genes. It is shown that PIAS1 is required for the appropriate localization and retention of Msx1 at the nuclear periphery in myoblast cells.

CTN-RNA, a mouse tissue-specific ~8 kb nuclear-retained poly(A)(super +) RNA that regulated the level of its protein-coding partner was identified. Findings revealed a role of the cell nucleus in harboring RNA molecules that were not immediately needed to produce proteins but whose cytoplasmic presence was required upon physiologic stress, thus highlighting an important paradigm for the role of a nuclear-retained stable RNA transcript in regulating gene expression.

Although mammalian urothelia are generally considered impermeable to urinary constituents, in vivo studies in several species suggest urothelial transport of water, urea, and solutes under certain conditions. This study investigates the expression, localization, and regulation of urea transporter-B (UT-B) in rat renal pelvis, ureter, and bladder tissues. Immunoblots of homogenates of tissues identified characteristic ~40-to 55- and ~32-kDa bands in the ureter, bladder, and renal inner medulla, but not renal cortex. UT-B was localized by immunocytochemistry and was strongly expressed in all cell membranes (and to a limited extent in intracellular vesicles in the cytoplasm) of epithelial cells lining the rat bladder, ureter, and renal pelvis lumens except the apical membrane of the umbrella cells. It was also present in single-layer papillary surface epithelial cells. There was no difference in immunoblot expression of UT-B in the bladder or ureteral homogenates between groups of rats fed high- or low-protein or high- or low-sodium diets. Water restriction resulted in an increase in UT-B expression in ureters (49%, P = 0.001) but not in bladders (14%, P = not significant). The functional role of UT-B in the genitourinary tract epithelia is unknown. UT-B may participate in the regulation of epithelial cell volume and osmolality, in the dissipation of urea gradients, and in possible net urea transport across uroepithelia. Western blot analysis; immunocytochemistry; urea transport

This paper analyzes the distributional effects of changes in the intensity of product market competition. The focus is on the interaction between imperfect competition in product markets and bargaining in the labor market. The main result is that, while a uniform intensification of product market competition increases employment, it may cause real wages to fall, in the short run as well as in the long run. This is especially likely if labor market regulations are favorable to workers. Therefore, product market and labor market regulations tend to reinforce each other politically, and compensatory fiscal transfers may be needed in order to enact employment-enhancing deregulation policies. JEL classification: E24; E25; J5 Keywords: Imperfect competition; Wage bargaining; Deregulation