Hydration status affects sodium, potassium, and chloride transport across rat urothelia

Abstract

Recent data suggest possible net transport of urinary constituents across mammalian urinary tract epithelia (urothelia). To evaluate the effect of animal hydration status on such transport, we instilled urine collected during 2-day water deprivation, water loading, or ad libitum water intake into isolated in situ bladder(s) of groups of rats undergoing one of the same three hydration states. After 1-h bladder dwell, we retrieved the urine and measured differences in volume and solute concentrations between instilled and retrieved urine. We previously reported results regarding changes in urine volume and net urea and creatinine transport and herein report the results of net urinary sodium, potassium, and chloride transport in the same animals. During water-loading conditions, urinary concentrations of Na, K, and Cl rose 4.9 (30.7%), 2.6 (16.5%), and 6.0 meq/l (26.8%), respectively, indicating urothelial secretion into urine. During ad libitum water intake, urinary K and Cl concentrations fell 33.6 (14.8%) and 28.4 meq/l (12%), respectively (Na did not change), and during water deprivation urine Na, K, and Cl concentrations fell dramatically by 53.2 (18.6%), 159.4 (34.6%) and 133.7 meq/l (33.8%), respectively, reflecting urothelial reabsorption of each ion. For each ionic species, two factors independently influenced transport: instilled urinary ion concentration and animal hydration state. These results demonstrate significant regulated ion transport across mammalian urothelia, support the notion that lower urinary tract modifies final urine, and suggest that the lower urinary tract may play a role in local and whole animal solute homeostasis.

Is electrolyte transfer across the urothelium important?: ICI‐RS 2015

“…Na + transport across ex vivo rabbit urothelial tissue and water permeability of human bladder were demonstrated several decades ago. Investigation of the permeability of intact rabbit bladder urothelium by Negrete et al showed that this was low under normal conditions, consistent with the urothelium acting as an effective barrier. In vivo studies of animals under conditions of water deprivation or water loading have also been employed to investigate the permeability of the bladder to water and several ions.…”

“…An interesting study of rats during water deprivation, water loading, or ad libitum H 2 O involved urine collection and its subsequent instillation into isolated in situ bladders from animals in the corresponding condition. Measurements of Na + , K + , and Cl − indicated that (1) the instilled urinary ion concentrations and (2) animal hydration status influenced the degree of water reabsorption across the urothelium leading the authors to conclude that urine composition was modified in the lower urinary tract …”

Aquaporin‐2 plays an important role in water transportation through the bladder wall in rats

“…Therefore, it was hypothesized that some channels in the urothelium function in the condition of full‐filled (distended) bladder because AQPs transport water only. Urea, sodium, and chlorine move across rat urothelial cells, but the underlying mechanism has not been elucidated. The epithelial sodium channel (ENaC) mediates sodium transport across the apical membrane of the urinary bladder epithelium .…”

The urothelium of a hibernator: the American black bear

“…; Spector et al. , , , ). Thus, at least small quantities of vectorial solute and water transport across urinary tract urothelia may be a feature of most or all mammalian species and the hibernating bear may or may not have unique urothelial transport capabilities enabling the net transport of urinary constituents.…”