The mechanism by which leptin increases ATP-sensitive K ؉ (K ATP ) channel activity was investigated using the insulin-secreting cell line, CRI-G1. Wortmannin and LY 294002, inhibitors of phosphoinositide 3-kinase (PI3-kinase), prevented activation of K ATP channels by leptin. The inositol phospholipids phosphatidylinositol bisphosphate and phosphatidylinositol trisphosphate (PtdIns(3,4,5)P 3 ) mimicked the effect of leptin by increasing K ATP channel activity in whole-cell and insideout current recordings. LY 294002 prevented phosphatidylinositol bisphosphate, but not PtdIns(3,4,5)P 3 , from increasing K ATP channel activity, consistent with the latter lipid acting as a membrane-associated messenger linking leptin receptor activation and K ATP channels. Signaling cascades, activated downstream from PI 3-kinase, utilizing PtdIns(3,4,5)P 3 as a second messenger and commonly associated with insulin and cytokine action (MAPK, p70 ribosomal protein-S6 kinase, stress-activated protein kinase 2, p38 MAPK, and protein kinase B), do not appear to be involved in leptin-mediated activation of K ATP channels in this cell line. Although PtdIns(3,4,5)P 3 appears a plausible and attractive candidate for the messenger that couples K ATP channels to leptin receptor activation, direct measurement of PtdIns(3,4,5)P 3 demonstrated that insulin, but not leptin, increased global cellular levels of PtdIns(3,4,5)P 3 . Possible mechanisms to explain the involvement of PI 3-kinases in K ATP channel regulation are discussed.The hormone leptin, secreted by adipocytes, has a major influence on body weight homeostasis (1, 2). Although the hypothalamus is considered the main target for leptin, particularly with respect to body weight regulation, it is clear that this hormone has distinct actions on other peripheral, target organs. There have been several reports that leptin reduces insulin secretion from pancreatic beta cells (3-6), although this view is not shared by all investigators (7). One mechanism proposed to explain the leptin-induced reduction in insulin secretion is via activation of ATP-sensitive K ϩ (K ATP ) channels (8, 9). This increase in potassium current results in beta cell hyperpolarization, reduced calcium entry, and hence decreased insulin secretion. In addition, there are features common to both insulin-secreting cells and leptin-sensitive hypothalamic neurones (10, 11), most notably glucose responsiveness and the presence of K ATP channels, which are activated by exposure of the cells to leptin. The apparent involvement of both leptin receptors and K ATP channel activation in key systems involved in metabolic homeostasis has led us to examine the likely signal transduction pathways underlying this effect.The leptin receptor belongs to the class I cytokine receptor superfamily (1, 2), members of which are thought to signal via janus-tyrosine kinases. Activated janus-tyrosine kinases can mediate signaling via insulin receptor substrate proteins (12-14), which following tyrosine phosphorylation become docking sites for Sr...

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The prevalence of lower urinary tract storage disorders such as overactive bladder syndrome and urinary incontinence significantly increase with age. Previous studies have demonstrated age-related changes in detrusor function and urothelial transmitter release but few studies have investigated how the urothelium and sensory pathways are affected. The aim of this study was to investigate the effect of ageing on urothelial-afferent signalling in the mouse bladder. Three-month-old control and 24-month-old aged male mice were used. In vivo natural voiding behaviour, sensory nerve activity, urothelial cell function, muscle contractility, transmitter release and gene and protein expression were measured to identify how all three components of the bladder (neural, contractile and urothelial) are affected by ageing. In aged mice, increased voiding frequency and enhanced low threshold afferent nerve activity was observed, suggesting that ageing induces overactivity and hypersensitivity of the bladder. These changes were concurrent with altered ATP and acetylcholine bioavailability, measured as transmitter overflow into the lumen, increased purinergic receptor sensitivity and raised P2X3 receptor expression in the urothelium. Taken together, these data suggest that ageing results in aberrant urothelial function, increased afferent mechanosensitivity, increased smooth muscle contractility, and changes in gene and protein expression (including of P2X3). These data are consistent with the hypothesis that ageing evokes changes in purinergic signalling from the bladder, and further studies are now required to fully validate this idea.

Objective• To investigate the direct effect of onabotulinumtoxinA (OnaBotA) on bladder afferent nerve activity and release of ATP and acetylcholine (ACh) from the urothelium. Materials and Methods• Bladder afferent nerve activity was recorded using an in vitro mouse preparation enabling simultaneous recordings of afferent nerve firing and intravesical pressure during bladder distension.• Intraluminal and extraluminal ATP, ACh, and nitric oxide (NO) release were measured using the luciferin-luciferase and Amplex ® Red assays (Molecular Probes, Carlsbad, CA, USA), and fluorometric assay kit, respectively.• OnaBotA (2U), was applied intraluminally, during bladder distension, and its effect was monitored for 2 h after application.• Whole-nerve activity was analysed to classify the single afferent units responding to physiological (low-threshold [LT] afferent <15 mmHg) and supra-physiological (high-threshold [HT] afferent >15 mmHg) distension pressures. Results• Bladder distension evoked reproducible pressure-dependent increases in afferent nerve firing.• After exposure to OnaBotA, both LT and HT afferent units were significantly attenuated.• OnaBotA also significantly inhibited ATP release from the urothelium and increased NO release. Conclusion• These data indicate that OnaBotA attenuates the bladder afferent nerves involved in micturition and bladder sensation, suggesting that OnaBotA may exert its clinical effects on urinary urgency and the other symptoms of overactive bladder syndrome through its marked effect on afferent nerves.

β(3)-adrenoceptors are involved in mediating inhibitory effects of β-adrenoceptor agonists on detrusor contractions via the urothelium in pig bladder dome.

Gap junctions enable intercellular communication and play an important role in a variety of vital cellular functions including differentiation and the control of growth. These junctions are formed by a hexameric of proteins known as connexins. We investigated the distribution of the connexin 43 (Cx43) gap junction protein in renal cells and human kidney using the alkaline phosphatase anti-alkaline phosphatase immunohistochemical technique with a monoclonal antibody directed against the cytoplasmic domain of this antigen. Strong staining was demonstrated on the vascular endothelium, the smooth muscle of larger vessels and on glomerular epithelial cells. In addition, Cx43 was expressed on proximal tubular cells, glomerular endothelial cells and occasional cells infiltrating the interstitium. In areas of tubular atrophy there was increased staining for Cx43. Using reverse transcription-polymerase chain reaction we have also demonstrated that cultured human and rat mesangial cells and human proximal tubular cells express Cx43 messenger RNA. In summary, we have described for the first time the distribution of Cx43 in human kidney and cultured renal cells.

1 Bladder smooth muscle sensitivity to muscarinic agonists is increased in the overactive bladder. Treatment of rats with streptozotocin induces a diabetic state in which the bladder muscle is overactive and also supersensitive to muscarinic agonists. This study has examined bladder contraction, muscarinic receptor density and receptor/G-protein coupling in the streptozotocin-induced overactive bladder of the rat. 2 Diabetes was induced by a single intraperitoneal dose of streptozotocin. Seven days later contraction of isolated detrusor muscle strips was assessed in tissue bath experiments, while receptor density was assayed in saturation experiments with [3H]-QNB (quinuclidinyl benzilate, L-[benzilic-4,4'-3H]) and receptor/G-protein coupling was determined in agonist displacement experiments with this radioligand. 3 Isolated detrusor strips from diabetic animals displayed an enhanced degree of spontaneous activity (0.060 +/- 0.016 g mg(-1), compared with 0.015 +/- 0.004 g mg(-1), P < 0.05). Carbachol produced contractile responses in tissues from both control and diabetic rats, but the diabetic tissues were more sensitive to this agonist, the pEC50 being 6.52 +/- 0.17 compared with 5.93 +/- 0.06 in controls (P < 0.001). Maximum responses to carbachol were similar in both groups of animals. The increase in carbachol potency was accompanied by a 40% increase in receptor density from 158 +/- 5 to 221 +/- 22 fmol mg(-1) protein (P < 0.05), but this was not enough to fully account for the change in tissue sensitivity. 4 In the absence of GTP-gamma-S, carbachol displaced [3H]-QNB from two binding sites, the high-affinity site (pKi = 7.06 +/- 0.26) which represents the receptors coupled to G-proteins made up 43.1 +/- 5.9% of the total binding sites in control tissues and this value was similar (41.0 +/- 4.0%) in the diabetic tissues (pKi = 6.64 +/- 0.31). In the presence of GTP-gamma-S, carbachol displaced [3H]-QNB from a single binding site which had a low-affinity, similar to the low-affinity site observed in the absence of GTP-gamma-S. 5 These data demonstrate that detrusor supersensitivity is observed after only 1 week of untreated diabetes in the rat. The overactivity is associated with an enhanced sensitivity to carbachol, which is partly explained by an increase in receptor density, but there appears to be no change in receptor/G-protein coupling.