Membrane potential of rat urinary bladder epithelial cells

Strain differences in sensitivity to the promoting effect of sodium L-ascorbate in a two-stage rat urinary bladder carcinogenesis model

Rat strain differences in sensitivity to the promoting effect of sodium L-ascorbate (SA) on the development of urinary bladder tumors were investigated. In experiment 1, WS/Shi (WS), ODS/Shiod/od (ODS), and LEW/Crj (LEW) rats were initiated with 0.05% N-butyl-N-(4-hydroxybutyl)-nitrosamine (BBN) in their drinking water and subsequently given basal Oriental MF diet (M) with or without a 5% SA supplement. In LEW rats the SA treatment increased the induction of neoplastic lesions in the urinary bladder, whereas WS and ODS animals proved unresponsive to its promoting effects. In experiment 2, WS and F344 rats were maintained on two kinds of commercial basal diets, M and CLEA CA-1 (C), during administration of SA, since dietary factors can influence promoting effects. Feeding M during the promotion period in F344 rats yielded significantly more neoplastic lesions than feeding C, but in WS rats no such dietary influence was apparent. In experiment 3, strain differences in biosynthesis of alpha-2u-globulin (alpha 1a-g) were assessed because both alpha 2a-g in the urine and administration of sodium salts of organic acids such as SA have been reported to be involved in tumor promotion. Immunohistochemical analysis of renal tubules and Western blotting analysis of urine revealed the presence of alpha 2a-g in all three strains examined. These data suggest that differences in susceptibility to promotion are due to genetic factors rather than dietary factors and the ability to synthesize alpha 2a-g.

Effects of Na saccharin feeding and urine on barrier properties of excised rat urinary bladder

When male rats of certain strains are fed a diet with 3% or more Na saccharin, their urinary bladders develop epithelial hyperplasia and a greater incidence of tumors. Since the daily dose of saccharin is high, a link between tumor formation and the disruption of urothelial physiologic and biochemical processes has been sought. We fed male and female Sprague-Dawley rats a saccharin-free or 7.5% Na saccharin diet for 1 month. Excised bladders were mounted in flux chambers and exposed to Krebs-Ringer bicarbonate solution (KRB) or urine. Bioelectric properties and 22Na, 36Cl, and [14C]mannitol or [3H]mannitol unidirectional fluxes were measured by conventional techniques. No differences were noted between bladders from male and female animals or between Na saccharin-fed animals and animals fed the saccharin-free diet. When both surfaces of the epithelium were exposed to KRB, transepithelial dc conductance fell over 4 hr to 50% of the initial value. Conductance averaged 1.4 mS/cm2. Transepithelial potential difference (PD) was usually lumen negative and averaged 0.7 mV. Unidirectional permeability coefficients for 36Cl, 22Na, and radiomannitol were symmetric, proportional to conductance, and followed a rank order compatible with unrestricted passive diffusion. Exposure of the bladder lumen to urine from animals fed saccharin-free or Na saccharin diet hyperpolarized the transepithelial PD by more than 5 mV and raised conductance nearly threefold. Permeability coefficients remained symmetric and compatible with passive diffusion. Exposure of the lumen to solutions with the K+, Na+, and Cl concentrations and osmolality of urine simulated the conductance and PD effects of urine. We conclude that Na saccharin feeding or urine with saccharin does not uniquely affect the permeability of the excised preparation. Small hydrophilic solutes appear to cross the bladder epithelium through paracellular channels which increase in aggregate area during exposure of the lumen to urine. The hyperpolarization induced by lumenal urine is the consequence of the transepithelial K+ gradient.