Culture of bladder epithelium from cystoscopic biopsies of patients with interstitial cystitis

Comparative genomic analysis of uropathogenic Escherichia coli strains from women with recurrent urinary tract infection

Introduction

Recurrent urinary tract infections (RUTIs) caused by uropathogenic Escherichia coli are costly public health problems impacting patients' quality of life.

Aim

In this work, a comparative genomics analysis of three clinical RUTI strains isolated from bladder biopsy specimens was performed.

Materials and methods

One hundred seventy-two whole genomes of urinary tract E. coli strains were selected from the NCBI database. The search for virulence factors, fitness genes, regions of interest, and genetic elements associated with resistance was manually carried out. The phenotypic characterization of antibiotic resistance, haemolysis, motility, and biofilm formation was performed. Moreover, adherence and invasion assays with human bladder HTB-5 cells, and transmission electron microscopy (TEM) were performed.

Results

The UTI-1_774U and UTI-3_455U/ST1193 strains were associated with the extraintestinal pathotypes, and the UTI-2_245U/ST295 strain was associated with the intestinal pathotype, according to a phylogenetic analysis of 172 E. coli urinary strains. The three RUTI strains were of clinical, epidemiological, and zoonotic relevance. Several resistance genes were found within the plasmids of these strains, and a multidrug resistance phenotype was revealed. Other virulence genes associated with CFT073 were not identified in the three RUTI strains (genes for type 1 and P fimbriae, haemolysin hlyA, and sat toxin). Quantitative adherence analysis showed that UTI-1_774U was significantly (p < 0.0001) more adherent to human bladder HTB-5 cells. Quantitative invasion analysis showed that UTI-2_245U was significantly more invasive than the control strains. No haemolysis or biofilm activity was detected in the three RUTI strains. The TEM micrographs showed the presence of short and thin fimbriae only in the UTI-2_245U strain.

Conclusion

The high variability and genetic diversity of the RUTI strains indicate that are a mosaic of virulence, resistance, and fitness genes that could promote recurrence in susceptible patients.

Expression and function of vascular endothelial growth inhibitor in aged porcine bladder detrusor muscle cells

Aging of the bladder detrusor muscle plays an important role in lower urinary tract symptoms in elderly people. Our previous work demonstrated that elderly patients have increased levels of vascular endothelial growth inhibitor (VEGI) in bladder tissue. Therefore, we hypothesized that VEGI may play a role in aging of the bladder detrusor muscle cells. This study aims to develop and characterize primary cultures of aged porcine bladder detrusor muscle cells in order to explore the expression and function of VEGI. Bladder samples from female pigs were divided into two groups: the aged group (Model) and the young group (Control). We confirmed β-galactosidase expression, a marker for senescence, in aged muscle cells (identified by α-smooth muscle actin (α-SMA) staining), but not in the young group. mRNA levels of VEGI-251 and death receptor 3 (DR3) were up-regulated (P < 0.05) and total cell protein levels of VEGI-251, DR3 and nuclear factor-kappa B [NF-κB (p65)], membrane protein levels of DR3, and nuclear protein levels of NF-κB (p65) were significantly higher (P < 0.01) in the Model cells compared to Control cells. In conclusion, we have established a method to culture aged detrusor muscle cells derived from porcine bladder. Higher levels of VEGI-251, DR3 and NF-κB (p65) were observed in the aged cells. VEGI-251 may function by increasing DR3 on cellular membranes and promoting the transfer of NF-κB into the nucleus. This suggests that VEGI may be a target for reversing the aging process of bladder detrusor muscle cells.

Epigallocatechin gallate attenuates interstitial cystitis in human bladder urothelium cells by modulating purinergic receptors

BACKGROUND

Epigallocatechin gallate (EGCG) has exhibited antitumor properties against bladder cancer. However, its effects in interstitial cystitis (IC) have not been investigated.

METHODS

Here, we performed repeated cystoscopy and re-biopsy of bladder mucosa before and after intravesical irrigation of EGCG in eight patients diagnosed with IC based on clinical and histopathologic assessments. Six normal bladder tissue samples were obtained from age-, race-, and sex-matched asymptomatic control subjects. IC symptom index was used to compare the therapeutic effect in IC patients. Patient-derived bladder epithelial cells were cultured and cell stretch experiments and ATP assays were performed. The expression of purinergic receptors X1, X2, and X3, and Y1, Y2, and Y11, in biopsied samples was detected by Western blotting and real-time polymerase chain reaction, respectively. Moreover, the expression of inducible NO synthase, phosphorylated Akt, and phosphorylated NF-κB was also assessed.

RESULTS

All EGCG-treated patients demonstrated different extents of remission of symptoms. We found a significant upregulation in P2X1, P2X2, and P2X3 receptor proteins and P2Y1, P2Y2, and P2Y11 receptor transcripts in IC patients. However, EGCG therapy attenuated the expression of all purinergic receptors. In addition, EGCG demonstrated prominent antioxidative and antiinflammatory effects via inhibition of the upregulation of iNOS and phosphorylated NF-κB. Furthermore, the stretch-activated release of ATP in cultured bladder urothelial cells was greater in cells derived from IC patients, compared with those from the control patients, but EGCG, at all concentrations tested, effectively abolished the increase in ATP release from stretched IC patient-derived cells.

CONCLUSIONS

Our study suggests that inhibition of the expression of purinergic receptors and ATP release in urothelial cells by EGCG supports further development of EGCG as a novel therapeutic option for IC.

Porcine bladder urothelial, myofibroblast, and detrusor muscle cells: characterization and ATP release

ATP is released from the bladder mucosa in response to stretch, but the cell types responsible are unclear. Our aim was to isolate and characterize individual populations of urothelial, myofibroblast, and detrusor muscle cells in culture, and to examine agonist-stimulated ATP release. Using female pig bladders, urothelial cells were isolated from bladder mucosa following trypsin-digestion of the luminal surface. The underlying myofibroblast layer was dissected, minced, digested, and cultured until confluent (10–14 days). A similar protocol was used for muscle cells. Cultures were used for immunocytochemical staining and/or ATP release investigations. In urothelial cultures, immunoreactivity was present for the cytokeratin marker AE1/AE3 but not the contractile protein α-smooth muscle actin (α-SMA) or the cytoskeletal filament vimentin. Neither myofibroblast nor muscle cell cultures stained for AE1/AE3. Myofibroblast cultures partially stained for α-SMA, whereas muscle cultures were 100% stained. Both myofibroblast and muscle stained for vimentin, however, they were morphologically distinct. Ultrastructural studies verified that the suburothelial layer of pig bladder contained abundant myofibroblasts, characterized by high densities of rough endoplasmic reticulum. Baseline ATP release was higher in urothelial and myofibroblast cultures, compared with muscle. ATP release was significantly stimulated by stretch in all three cell populations. Only urothelial cells released ATP in response to acid, and only muscle cells were stimulated by capsaicin. Tachykinins had no effect on ATP release. In conclusion, we have established a method for culture of three cell populations from porcine bladder, a well-known human bladder model, and shown that these are distinct morphologically, immunologically, and pharmacologically.

Bladder urothelial cells from patients with interstitial cystitis have an increased sensitivity to carbachol

AIMS

The presence of muscarinic receptors on bladder urothelial cells (BUC), suggests BUC may be a target for antimuscarinics. This study determined whether human BUC are responsive to a muscarinic agonist and if so, whether responses are altered in interstitial cystitis (IC) BUC.

METHODS

Primary urothelial cell cultures were established from cystoscopic biopsies. Normal (NB) and IC BUC were studied using calcium imaging techniques as a means to monitor the response to muscarinic receptor activation with the agonist, carbachol (CCh). Changes in intracellular Ca(2+) concentration ([Ca(2+)](i)) were measured with fura-2 ratiometric microfluorimetry. Dose-response curves (CCh dose vs. [Ca(2+)](i)) were measured in IC and NB BUC. Tolterodine was used to confirm the specificity (muscarinic versus nicotinic) of CCh evoked increases in [Ca(2+)](i).

RESULTS

CCh induced a dose-dependent increase in [Ca(2+)](i). Potency and efficacy of CCh was significantly greater in IC BUC. The maximal increase in [Ca(2+)](i) was 136.3 +/- 5.1% over baseline in 78 cells from 4 IC patients versus 92.4 +/- 4.8% over baseline in 67 cells from 4 NB subjects (P < 0.01). The EC50 of the evoked increase was 1.10 +/- 0.14 microM versus 3.36 +/- 0.72 microM (P < 0.01) in BUC from IC and NB controls, respectively. Removal of extracellular calcium or application of tolterodine, abolished CCh evoked increase in [Ca(2+)](i) in IC and NB BUC.

CONCLUSIONS

The greater sensitivity of IC BUC to CCh suggests that IC patholobiology may also include alterations muscarinic signaling. The physiologic sequelae of muscarinic activation in BUC need to be further investigated.

Augmented bladder urothelial polyamine signaling and block of BK channel in the pathophysiology of overactive bladder syndrome

Overactive bladder syndrome (OAB) is an idiopathic condition characterized by urinary urgency and urge incontinence. Detrusor overactivity has been traditionally described as the physiologic mechanism for OAB. However, the bladder urothelium (BU) may also be involved in the pathophysiology. This study measured polyamine signaling and its downstream effects on membrane conductivity in bladder urothelial cells (BUC) obtained from asymptomatic and OAB subjects. Immunohistofluorescence was used to measure ornithine decarboxylase (ODC) expression in BU. BUC, cultured from BU biopsies, were used for electrophysiologic studies. dl-alpha-Difluoromethylornithine (DFMO), spermine, or spermidine was used to modulate polyamine signaling in BUC. Results showed ODC overexpression in OAB BU. In OAB BUC, whole cell and cell-attached configuration showed significantly decreased currents. Using inside-out patches, outward currents increased significantly, suggesting a cytoplasmic source of the outward current block in OAB BUC. In control BUC, outward currents were mediated by the large-conductance calcium-activated potassium (BK) channel due to calcium dose-dependence and block by iberiotoxin. Spermidine and spermine blocked the outward current in normal BUC in dose-dependent fashion. Conversely, DFMO significantly increased (P < 0.01) outward currents in OAB BUC both in cell-attached and in whole cell configuration. The outward currents in DFMO-treated-OAB BUC could be significantly reduced (P < 0.05) by adding back spermidine and spermine. These data suggest that polyamine signaling is upregulated in OAB urothelium and OAB BUC. Furthermore, polyamines in BUC block the BK channel. Targeting of bladder urothelial polyamine signaling may represent a novel approach for OAB treatment based on pathophysiologic mechanisms.

Changes in adenosine triphosphate-stimulated ATP release suggest association between cytokine and purinergic signaling in bladder urothelial cells

OBJECTIVES

To determine whether antiproliferative factor (APF) or epidermal growth factor (EGF) can induce changes in purinergic signaling in normal bladder urothelial cells (BUCs) and/or whether antagonizing EGF activity or blocking adenosine triphosphate (ATP)-purinergic receptors can induce changes in purinergic signaling in interstitial cystitis (IC) cells.

METHODS

IC and normal BUCs were obtained from patients' bladder biopsy specimens. IC BUCs were treated with genistein, which antagonizes EGF's activity, and normal BUCs were treated with EGF, mock APF, or APF. Suramin, which antagonizes ATP activity, was used to treat the APF-treated normal BUCs. ATP release was determined by stimulating the BUCs with 30 microM ATP and then collecting the supernatant for a 3-hour period. ATP quantification was measured by luciferin-luciferase assay. Purinergic receptor P2X, ligand-gated ion channel, 3 (P2X3) expression on BUCs was determined by fluorescence-activated cell sorting.

RESULTS

Genistein treatment of IC BUCs resulted in significantly decreased ATP release, thus reverting IC cells to a normal purinergic signaling phenotype. Conversely, normal BUCs treated with EGF or APF resulted in significantly increased ATP release and P2X3 expression, converting normal BUCs to an IC phenotype. Also, suramin treatment of APF-treated normal BUCs significantly reduced ATP release.

CONCLUSIONS

Genistein and suramin reversed the augmented ATP release in IC BUCs and APF-treated normal BUCs, respectively, suggesting the possibility of intravesical use of these agents in IC treatment. EGF and APF induced augmented purinergic signaling in normal BUCs, as determined by increased ATP release and increased P2X3 expression. These data suggest an association between cytokines and purinergic signaling in human BUCs that should be explored further.

Defects in muscarinic receptor cell signaling in bladder urothelial cancer cell lines

INTRODUCTION

To explore muscarinic receptor signaling in 4 bladder cancer cell lines, bladder urothelial cells (BUC) have been shown to release and respond to various putative neurotransmitters.

METHODS

Reverse transcription-polymerase chain reaction was used to detect the presence of m1-m5 transcripts in the J82, RT4, T24, and 5637 lines of cancer BUC. Immunofluorescence was used to detect expression of m3 protein. Cancer and normal BUC were stimulated with carbachol (100 microM), a muscarinic agonist. Carbachol-evoked changes in intracellular calcium ([Ca(2+)](i)) levels were measured using fura-2 ratiometric microfluorimetry. Transfection of J82 cells with m3 plasmid was performed, and changes in carbachol-evoked [Ca(2+)](i) were re-examined.

RESULTS

None of the cancer cell lines expressed m3 transcripts, unlike normal BUC, which expressed m3. None of the 4 bladder cancer cell lines responded to carbachol. However, 47% of normal BUC responded to carbachol. The m3-transfected J82 cells expressed both m3 transcript and protein. Thirteen percent of m3-transfected J82 cells responded to carbachol.

CONCLUSIONS

This is the first description of altered muscarinic signaling in cancer BUC. Unlike normal BUC, bladder urothelial cancer cells neither expressed m3 transcript nor responded to carbachol, as measured by changes in [Ca(2+)](i). We could partially reverse this defect in one of the cancer cell lines, J82, by transfecting these cells with the m3 plasmid. Although the effects of muscarinic receptor signaling on urothelial cell are unknown, this signaling pathway may play a role in urothelial cell adhesion similar to that in keratinocytes.

Dysfunction of bladder urothelium and bladder urothelial cells in interstitial cystitis

The human bladder urothelium (BU) and bladder urothelial cells (BUCs) play an important role in the normal functioning of bladder including bladder storage. Current evidence in interstitial cystitis (IC) supports multiple abnormalities in bladder urothelial physiology. These data have come primarily from human studies. The discovery of a novel protein termed the antiproliferative factor (APF) uniquely expressed by IC BUCs is extremely important. APF induces increased permeability of normal BUCs grown in culture. Furthermore, APF regulates expression of other cytokines, including upregulating heparin-binding epidermal growth factor-like growth factor and downregulating epidermal growth factor by BUCs. These cytokine abnormalities were also related to increases in purinergic (adenosine triphosphate) signaling, which could mediate increased bladder sensation. Recent studies of uroplakins, which are specialized proteins expressed only in the apical urothelial cells, suggest that uroplakins play a role in the barrier function of the BU. It is also conceivable that alterations in uroplakins may result in bladder symptoms related to increased permeability or decreased protective function. As the body of knowledge about BU and BUC function increases, novel therapies targeting urothelial cells should become clinically feasible.

EGF and HB-EGF modulate inward potassium current in human bladder urothelial cells from normal and interstitial cystitis patients

Interstitial cystitis (IC) is an idiopathic condition characterized by bladder hyperalgesia. Studies have shown cytokine and purinergic signaling abnormalities in cultured bladder urothelial cells (BUC) from IC patients. We performed single-cell electrophysiological studies in both normal and IC BUC. A strongly inward rectifying potassium current with conductance of the Kir2.1 channel was identified in normal BUC. This current was significantly reduced in IC BUC. Kir2.1 protein and mRNA were detected in both IC and normal BUC. Epidermal growth factor (EGF) caused a dose-dependent decrease in the inward potassium current in normal BUC. EGF is secreted in higher amounts by IC BUC and is known to decrease Kir2.1 conductance by phosphorylation of Kir2.1. Genistein, a nonspecific phosphorylation inhibitor, increased the inward potassium current in IC BUC and blocked the effect of EGF on normal BUC. Treatment of IC BUC with heparin-binding epidermal growth factor-like growth factor (HB-EGF), previously shown to be secreted in lower amounts by IC BUC, significantly increased inward potassium current. These data show that the inward potassium current in BUC can be modulated by EGF and HB-EGF. Changes in BUC membrane potassium conductance caused by altered levels of EGF and HB-EGF may therefore play a role in the pathophysiology of IC.

Augmented extracellular ATP signaling in bladder urothelial cells from patients with interstitial cystitis

Interstitial cystitis (IC) is an idiopathic hypersensory condition of the bladder associated with increased urinary ATP and increased stretch-activated ATP release by bladder urothelial cells (BUCs), suggesting augmented purinergic signaling in the bladder. To test this theory further, monolayers of cultured BUCs derived from bladder biopsies obtained from patients with IC and control patients were stimulated with 10-30 microM ATP with subsequent measurement of extracellular ATP levels using the luciferin-luciferase assay. Stimulation with 30 microM ATP resulted in IC supernatant containing several-fold more ATP than control BUCs initially, followed by a slower decrease in ATP levels. This difference in ATP levels was not completely due to activity of cellular ecto-ATPase, because blockade with ARL67156 did not normalize the difference. Exposure to hypotonic solutions resulted in similar extracellular ATP concentrations in IC and control BUCs, but there was a slower decrease in ATP levels in IC supernatants. Treatment of IC BUCs with 10-40 microM suramin, a nonspecific P2 receptor antagonist, significantly attenuated the IC BUC response to extracellular ATP, restoring IC BUCs to a control phenotype. Pretreatment of IC BUCs with 20 ng/ml of heparin-binding EGF-like growth factor (HB-EGF), which previously has been shown to be decreased in IC urine specimens, also restored IC BUCs to a control phenotype with respect to response to ATP stimulation. In conclusion, IC BUCs have augmented extracellular ATP signaling that could be blocked by suramin and HB-EGF. These findings suggest the possible development of future novel therapeutic techniques.

Up-Regulation of P2X 3 Receptor During Stretch of Bladder Urothelial Cells From Patients With Interstitial Cystitis

PURPOSE

Extracellular adenosine triphosphate (ATP) can act through the purinergic receptor subtype P2X3 to transmit a pain signal to the central nervous system. Bladder urothelial cells (BUCs) from patients with interstitial cystitis (IC) patients have augmented release of ATP during in vitro stretch. We queried whether P2X3 receptor subtype exists on cultured BUCs. Furthermore, we asked whether P2X3 expression can be altered by in vitro stretch and whether there exists a difference in expression between IC and control BUCs.

MATERIALS AND METHODS

BUCs from 4 IC and 5 control subjects were cultured according to established cell culture techniques. After cells were grown to confluence they were stretched on an in vitro stretch machine at 20% elongation for up to 96 hours. Cells were harvested at various times, and immunofluorescence and Western blots were performed for P2X3 expression. Band densitometry normalized to the actin band was performed using software. To confirm P2X3 expression in a whole cell preparation flow cytometry and fluorescence activated cell sorter analysis were used.

RESULTS

P2X3 was expressed in cultured BUCs. With stretch P2X3 expression increased in IC BUCs more than in control BUCs. Using relative densitometry units normalized for actin expression in the Western blots stretch of IC BUCs resulted in 66% more expression of P2X3 than any other experimental condition (p = 0.003). By fluorescence activated cell sorter analysis stretched IC BUCs had the highest P2X3 fluorescence activity (30%) compared with unstretched IC (2.4%, p = 0.003), stretched control (9.7%, p = 0.009) and unstretched control (2.3%, p = 0.003) BUCs.

CONCLUSIONS

These data show that P2X3 subunits expressed by cultured IC BUCs are up-regulated during in vitro stretch. Augmented ATP signaling in the bladder may explain IC symptoms. Furthermore, this study further supports the hypothesis that urothelial cells can phenotypically mimic sensory neurons.

Phospholipid metabolite production in human urothelial cells after protease-activated receptor cleavage

Our laboratory demonstrated previously that stimulation of protease-activated receptors (PARs) on the human urothelial carcinoma cell line RT4 results in activation of a calcium-independent phospholipase A(2) (iPLA(2)), leading to arachidonic acid and PGE(2) release. In this study, we have examined PAR activation in normal human urothelial cells (HUR) leading to the production of inflammatory or cytoprotective phospholipid metabolites. The presence of both PAR-1 and PAR-2 on HUR was confirmed by immunoblotting. Stimulation of PAR-1 with thrombin or PAR-2 by tryptase leads to activation of a membrane-associated iPLA(2) and the production of platelet-activating factor, arachidonic acid, and PGE(2). These responses were all blocked by pretreatment with the iPLA(2)-selective inhibitor bromoenol lactone. Thus stimulation of PAR-1 or PAR-2 on HUR leads to iPLA(2)-catalyzed phospholipid hydrolysis, resulting in the production of metabolites that may mediate inflammation or provide cytoprotection to the bladder.

Effects of dimethyl sulphoxide and heparin on stretch-activated ATP release by bladder urothelial cells from patients with interstitial cystitis

OBJECTIVE

To determine whether dimethyl sulphoxide (DMSO) and heparin reduce the greater stretch-activated ATP release in interstitial cystitis (IC), as ATP serves as a nocio-neurotransmitter in the bladder, and thus explain their beneficial effects in patients with IC (a disease characterized by hypersensory bladder symptoms).

MATERIALS AND METHODS

Bladder epithelia in IC release more ATP in response to stretch than do control samples. Both DMSO and heparin are used intravesically to treat IC; such agents can modulate urothelial function because they directly contact bladder urothelium. Biopsies taken from patients with IC and from control subjects were grown in primary cultures using established cell-culture techniques. Cultured urothelial cells were stretched with the Flexcell device (Flexcell International Corp., McKeesport, PA, USA) and supernatant ATP was measured, using a luciferin-luciferase assay. DMSO (0.1%, 0.5% and 1%) or heparin (50, 200, 800 and 1600 U) was added to the cells at the start of the stretch experiments and the ATP released into the supernatant measured. Cell viability was also determined using Trypan Blue staining.

RESULTS

IC cells released significantly more ATP in response to stretch than did control cells. This increased release of ATP by stretched IC cells was significantly blocked by adding DMSO or heparin at all concentrations used. Heparin appeared to have a greater dose-dependent effect on ATP release than did DMSO.

CONCLUSIONS

These findings are consistent with the hypothesis that the urothelium provides sensory input via ATP release and that this process is increased in IC. Furthermore, stretch-activated ATP release was blocked by adding DMSO and heparin, both intravesical agents commonly used to treat the symptoms of IC. This study supports the notion that purinergic-targeted therapy is warranted in treating IC. Further studies are needed to determine the mechanisms of increased ATP release by IC urothelial cells.

Effect of doxazosin on stretch-activated adenosine triphosphate release in bladder urothelial cells from patients with benign prostatic hyperplasia

OBJECTIVES

Recent data suggest that the bladder urothelium may have a sensory function by way of release of adenosine triphosphate (ATP) during stretch, which then acts as a sensory neurotransmitter. Because benign prostatic hyperplasia (BPH) can give rise to irritative (hypersensory) voiding patterns, we questioned whether the bladder urothelium from patients with BPH released more ATP during in vitro stretch and whether doxazosin, an alpha(1)-adrenoceptor blocker, affects this purinergic mechanism.

METHODS

Bladder urothelial biopsies from patients with BPH (n = 4) and controls (n = 4) were cultured using established techniques. In vitro stretch was performed with a Flexcell 2000 device that uses vacuum to deform the cell growth surface to impart a stretch force. Doxazosin (5 microM and 20 microM) was added to cells, and supernatants were collected at various points for ATP assay. ATP was assayed using the luciferin-luciferase reaction. ATP data were normalized to the time 0 value and expressed as a percentage of the baseline value.

RESULTS

After 96 hours of stretch, the BPH urothelial cells released significantly more ATP than did the control urothelial cells (62.6% +/- 11.2% versus 24.2% +/- 5.4%, P = 0.005) and nonstretched BPH urothelial cells (62.6% +/- 11.2% versus 15.1% +/- 5.1%, P = 0.004). The augmented release of ATP by stretched BPH bladder urothelial cells was completely blocked by treatment with 20 microM doxazosin.

CONCLUSIONS

Irritative voiding secondary to BPH may arise from increased ATP release by bladder urothelium during stretch. Doxazosin inhibits ATP release by way of an unknown mechanism that may or may not involve the alpha1-adrenoreceptor. Treatment for hypersensory voiding symptoms secondary to BPH might also target the urothelial purinergic pathway.

Primary uroepithelial cultures. A model system to analyze umbrella cell barrier function

Despite almost 25 years of effort, the development of a highly differentiated and functionally equivalent cell culture model of uroepithelial cells has eluded investigators. We have developed a primary cell culture model of rabbit uroepithelium that consists of an underlying cell layer that interacts with a collagen substratum, an intermediate cell layer, and an upper cell layer of large (25-100 micrometer) superficial cells. When examined at the ultrastructural level, the superficial cells formed junctional complexes and had an asymmetric unit membrane, a hallmark of terminal differentiation in bladder umbrella cells. These cultured "umbrella" cells expressed uroplakins and a 27-kDa uroepithelial specific antigen that assembled into detergent-resistant asymmetric unit membrane particles. The cultures had low diffusive permeabilities for water (2.8 x 10(-4) cm/s) and urea (3.0 x 10(-7) cm/s) and high transepithelial resistance (>8000 Omega cm2) was achieved when 1 mM CaCl2 was included in the culture medium. The cell cultures expressed an amiloride-sensitive sodium transport pathway and increases in apical membrane capacitance were observed when the cultures were osmotically stretched. The described primary rabbit cell culture model mimics many of the characteristics of uroepithelium found in vivo and should serve as a useful tool to explore normal uroepithelial function as well as dysfunction as a result of disease.