The regulation of ATP release from the urothelium by adenosine and transepithelial potential

Abstract

What's known on the subject? and What does the study add?• Stretch of the urothelium, as occurs during bladder filling, is associated with a release of ATP that is postulated to act as a sensory neurotransmitter. The regulation of ATP release is poorly understood and in particular if there is a feedback mechanism provided by ATP itself.• Adenosine, a breakdown product of ATP, is a potent inhibitor of stretch-induced ATP release, acting through and A1 receptor; endogenous levels are about 0.6mM . Data are consistent with ATP release relying on the rise of intracellular Ca2+. Transepithelial potential also controls ATP release, also acting via an A1 receptor-dependent pathway. Objectives• To test the hypothesis that distension-induced ATP release from the bladder urothelium is regulated by adenosine as well as changes to transurothelial potential (TEP).• To examine the role of changes to intracellular [Ca 2+ ] in ATP release. Materials and Methods• Rabbit urothelium/suburothelium membranes were used in an Ussing chamber system. Distension was induced by fluid removal from the chamber bathing the serosal (basolateral) membrane face.• The TEP and short-circuit current were measured. ATP was measured in samples aspirated from the serosal chamber by a luciferin-luciferase assay. • Intracellular [Ca 2+ ] was measured in isolated urothelial cells using the fluorochrome Fura-2. All experiments were performed at 37°C. Results• Distension-induced ATP release was decreased by adenosine (1-10 mM) and enhanced by adenosine deaminase and A1-(but not A2-) receptor antagonists.• Distension-induced ATP release was reduced by 2-APB, nifedipine and capsazepine; capsaicin induced ATP release in the absence of distension.• ATP and capsaicin, but not adenosine, generated intracellular Ca 2+ transients; adenosine did not affect the ATP-generated Ca 2+ transient.• ATP release was dependent on a finite transepithelial potential. Changes to TEP, in the absence of distension, generated ATP release that was in turn reduced by adenosine. Conclusion• Adenosine exerts a powerful negative feedback control of ATP release from the urothelium via A1 receptor activation.• Distension-induced ATP release may be mediated by a rise of the intracellular [Ca 2+ ].• Modulation of distension-induced ATP release by adenosine and TEP may have a common pathway.

P2Y Receptor Modulation of ATP Release in the Urothelium

“…Adding to the complexity of P2 receptor signalling, further breakdown of ADP to AMP and adenosine was seen to inhibit ATP release. Inhibition of ATP release by adenosine has been previously reported in rabbit bladder mucosal strips [20]. These findings indicate that while the initial breakdown of ATP to ADP may exert positive feedback for ATP release which is short lived, further breakdown of ATP to AMP and adenosine may provide negative feedback for ATP release.…”

“…The function of these receptors on the urothelium is currently undetermined. In addition, adenosine formed from the breakdown of ATP binds to P1 receptors which are also expressed on the urothelium [20]. …”

Functional Role for Piezo1 in Stretch-evoked Ca2+ Influx and ATP Release in Urothelial Cell Cultures

“…ATP released from urothelial cells depends on the increase in intracellular Ca 2ϩ concentrations (26,49) and plays an important role for signal transduction to afferent nerve endings; ATP regulates bladder functions, including the micturition reflex and nonvoiding contractions (44). In the present study, the amount of ATP released from the urothelium paralleled the changes in the cytosolic Ca 2ϩ concentrations at a 200-m stretch length.…”

Purinergic signalling in the urinary bladder

“…Since the first report of distension-evoked ATP release from the urothelium (Ferguson et al, 1997), abundant recent evidence has accumulated supporting a role for urothelially derived release of ATP in autocrine and paracrine signaling within the lower urinary tract Cheng et al, 2014;Dunning-Davies et al, 2013;Mansfield and Hughes, 2014;Mc Latchie and Fry, 2014;McLatchie et al, 2014). Thus, ATP released from the urothelium may have an autocrine function and/or may act in a local paracrine way to influence afferent nerve, interstitial cell/myofibroblast, or detrusor smooth muscle function (Sui et al, 2014a,b).…”