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 (Kir 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 ϳ45-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 MAMMALIAN URINARY TRACT EPITHELIA (urothelia) has long been held to serve solely as a storage conduct for urine made by the kidney and, in particular, to prevent modification of urine by inhibiting net flux of water and solutes across the epithelial cell luminal membrane (7). The barrier(s) preventing transepithelial flux of urine constituents have been shown to include: the lumenal membrane (containing unique uroplakin proteins) of the large ("umbrella") cells lining the urinary tract lumen (12), tight junctions adjoining the umbrella cells, and a glycosaminoglycans layer overlying and adjacent to the lumenal membrane (13, reviewed in Ref. 17). Evidence for the effectiveness of these barriers, which have been thought to be passive in nature and not to utilize or require membrane transporters, comes from Ussing chamber studies documenting very low urothelial permeability to water, ions, and nonelectrolytes and very high transepithelial cell resistance in stretched bladders and apical membrane endosomes obtained from rabbits under basal conditions (2, 24).However, although the permeabilities of urothelia for water and various urinary solutes may be low under basal conditions, urothelial permeabilities in animals subjected to dietary, physiological (e.g., water loading/water restricted), or other stress could be altered. Furthermore, urothelial cells are...

A 61-year-old woman with no past medical history was admitted with nonketotic hyperosmolar state that was complicated by seizures. At presentation, her serum glucose was 800 mg/dL with negative ketones. Glycosylated hemoglobin (HbA1c) was 14.1%. The patient was started on intravenous insulin and fluids. Serum insulin levels were not measured since the patient was already started on an insulin drip. She was also noted to have virilization. She had normal menarche, regular menses until menopause, and had delivered 4 children without any difficulty. Virilization developed gradually over 2 years, and the patient had been shaving daily for the past 1 year. There was no prior history of diabetes mellitus. Her weight was 176 pounds, with a height of 66 inches (body mass index of 28 kg/m 2 ). Physical examination showed temporal recessions, balding vertex, and a full beard ( Figure 1A through C). There was terminal hair on the chest, abdomen, and extremities ( Figure 1D and E). Clitoromegaly was present; however, her voice was normal. Acanthosis nigricans was absent, and there were no stigmata of Cushing syndrome. Serum total testosterone was 525 ng/dL (49-102), free testosterone measured 101 pg/mL (1.0-8.5), and bioavailable testosterone was 190 ng/dL (3-29). The rest of the work-up showed dehydroepiandrosterone measuring 314 g/dL (130-980), luteinizing hormone measuring 32.6 mIU/mL (14.4-62.2), follicle-stimulating hormone measuring 53.1 mIU/mL (25-160), and 24-hour urine free Cortisol of 20 g/d (Ͻ50). Pelvic examination was normal.