In the urinary bladder, the capsaicin-gated ion channel TRPV1 is expressed both within afferent nerve terminals and within the epithelial cells that line the bladder lumen. To determine the significance of this expression pattern, we analyzed bladder function in mice lacking TRPV1. Compared with wild-type littermates, trpv1(-/-) mice had a higher frequency of low-amplitude, non-voiding bladder contractions. This alteration was accompanied by reductions in both spinal cord signaling and reflex voiding during bladder filling (under anesthesia). In vitro, stretch-evoked ATP release and membrane capacitance changes were diminished in bladders excised from trpv1(-/-) mice, as was hypoosmolality-evoked ATP release from cultured trpv1(-/-) urothelial cells. These findings indicate that TRPV1 participates in normal bladder function and is essential for normal mechanically evoked purinergic signaling by the urothelium.

Diabetic bladder dysfunction (DBD), a prevalent complication of diabetes mellitus (DM), is characterized by a broad spectrum of symptoms including urinary urgency, frequency, and incontinence. As DBD is commonly diagnosed late, it is important to understand the chronic impact of DM on bladder tissues. While changes in bladder smooth muscle and innervation have been reported in diabetic patients, the impact of DM on the specialized epithelial lining of the urinary bladder, the urothelium (UT), is largely unknown. Quantitative polymerase chain reaction analysis and electron microscopy were used to evaluate UT gene expression and cell morphology 3, 9, and 20 wk following streptozotocin (STZ) induction of DM in female SpragueDawley rats compared with age-matched control tissue. Desquamation of superficial (umbrella) cells was noted at 9 wk DM, indicating a possible breach in barrier function. One causative factor may be metabolic burden due to chronic hyperglycemia, suggested by upregulation of the polyol pathway and glucose transport genes in DM UT. While superficial UT repopulation occurred by 20 wk DM, the phenotype was different, with significant upregulation of receptors associated with UT mechanosensation (transient receptor potential vanilloid subfamily member 1; TRPV1) and UT autocrine/paracrine signaling (acetylcholine receptors AChR-M2 and -M3, purinergic receptors P2X2 and P2X3). Compromised barrier function and alterations in UT mechanosensitivity and cell signaling could contribute to bladder instability, hyperactivity, and altered bladder sensation by modulating activity of afferent nerve endings, which appose the urothelium. Our results show that DM impacts urothelial homeostasis and may contribute to the underlying mechanisms of DBD. streptozotocin; urothelium; barrier; sensory; diabetic bladder dysfunction IN THE UNITED STATES alone it is estimated that approximately 19 million individuals, comprising both men and women, suffer from diabetes mellitus (DM) (13). DM is characterized by defects in the secretion of the hormone insulin by the pancreas and/or insulin signaling (53), which causes a dysregulation of cellular glucose uptake. Glucose is a large hydrophilic molecule that depends on specific glucose transporter (GLUT) proteins, present on the cell membrane, for cellular entry (12). From the GLUT family (13 cloned to date), GLUT4 is regulated by insulin and controls glucose uptake by skeletal muscle [which accounts for ϳ40% of total body mass (70)], cardiac muscle, and adipose tissue (75). Thus Type 1 and 2 diabetics are unable to efficiently transport glucose from the blood into these tissue groups (66) resulting in a state of hyperglycemia. Consequently, glucose inundates cells that express insulinindependent glucose transporters (such as GLUT1). Chronic elevation in cytosolic glucose leads to metabolic abnormalities such as osmotic and oxidative stress, thought to be factors that contribute to tissue injury and dysfunction associated with long-term DM (15, 61).The urinary bladder is one of th...

Parathyroid hormone (PTH) and FGF23 are the primary hormones regulating acute phosphate homeostasis. Human renal proximal tubule cells (RPTECs) were used to characterize the mechanism and signaling pathways of PTH and FGF23 on phosphate transport and the role of the PDZ protein NHERF1 in mediating PTH and FGF23 effects. RPTECs express the NPT2A phosphate transporter, ␣Klotho, FGFR1, FGFR3, FGFR4, and the PTH receptor. FGFR1 isoforms are formed from alternate splicing of exon 3 and of exon 8 or 9 in Ir-like loop 3. Exon 3 was absent, but mRNA containing both exons 8 and 9 is present in cytoplasm. Using an FGFR1c-specific antibody together with mass spectrometry analysis, we show that RPTECs express FGFR-␤1C. The data are consistent with regulated FGFR1 splicing involving a novel cytoplasmic mechanism. PTH and FGF23 inhibited phosphate transport in a concentration-dependent manner. At maximally effective concentrations, PTH and FGF23 equivalently decreased phosphate uptake and were not additive, suggesting a shared mechanism of action. Protein kinase A or C blockade prevented PTH but not FGF23 actions. Conversely, inhibiting SGK1, blocking FGFR dimerization, or knocking down Klotho expression disrupted FGF23 actions but did not interfere with PTH effects. C-terminal FGF23(180 -251) competitively and selectively blocked FGF23 action without disrupting PTH effects. However, both PTH and FGF23-sensitive phosphate transport were abolished by NHERF1 shRNA knockdown. Extended treatment with PTH or FGF23 down-regulated NPT2A without affecting NHERF1. We conclude that FGFR1c and PTHR signaling pathways converge on NHERF1 to inhibit PTH-and FGF23-sensitive phosphate transport and down-regulate NPT2A.Parathyroid hormone (PTH) 2 and FGF23 display two remarkable features: 1) PTH and FGF23 exhibit parallel inhibition of renal phosphate transport mediated by NPT2A (sodium-dependent phosphate transporter-2a) but opposing actions on 1,25(OH) 2 -vitamin D; 2) despite being structurally and functionally distinct classes of membrane-delimited receptors, PTH and FGF receptors activate kinases that obligatorily phosphorylate NHERF1 at conserved sites required for their phosphaturic action. Phosphorus is essential for growth and maintenance of the skeleton and for generating high energy phosphate compounds. Evolutionary adaptation in humans and other terrestrial vertebrates to phosphorus-rich diets involves cell and molecular mechanisms ensuring the efficient urinary elimination of excess inorganic phosphate. The renal proximal tubule is the primary site of phosphate homeostasis and hormone-dependent phosphate transport. The NPT2A sodium-dependent phosphate cotransporter (SLC34A1) in proximal tubules is regulated by PTH and FGF23 (1, 2). PTH and FGF23 reduce phosphate uptake by sequestering and down-regulating NPT2A, thereby enhancing urinary phosphate excretion (3, 4). PTH actions are mediated by its cognate G protein-coupled PTH receptor (PTHR) (5, 6). Both PKA and PKC have been implicated in PTH-dependent inhibition of NPT2A (7-12)....