AB274. SPR-01 Mechanosensitive release of adenosine 5'-triphosphate and other purines from the bladder urothelium

Objective: Adenosine 5'-triphosphate (ATP) is released from the bladder mucosa during bladder filling and is assumed to stimulate sensory neurons in the lamina propria and to regulate the apical delivery of fusiform vesicles in urothelial umbrella cells. As a parasympathetic cotransmitter, ATP contracts the detrusor smooth muscle. Therefore, extracellular ATP likely regulates the two phases of the micturition cycle (i.e., bladder filling and emptying) by different mechanisms. We recently demonstrated intraluminal release of purines in addition to ATP during bladder filling. The present study was designed to expand on previous works and evaluate simultaneously the release of ATP, ADP, AMP, nicotinamide adenine dinucleotide (NAD+)/ADP-ribose and adenosine from both sides of the urothelium during bladder filling.

Methods: The luciferin-luciferase assay method that is commonly used to evaluate ATP release in the bladder overlooks release of biologically-active purines that are different from ATP. Urothelial release of ATP is frequently studied in isolated bladder wall sheets mounted in Ussing chambers, which does not mimic typical bladder filling. In contrast, we determined release of purines in whole decentralized (ex vivo) mouse (C57/BL6) bladder preparations with removed detrusor smooth muscle that were filled with either 50 µL (low volume) or 200 µL (high volume) physiological solution at 15 µL/min. After distention, both extraluminal (bath fluid aliquots) and intraluminal fluids were collected and preserved with citric buffer (pH 4.0). The presence of multiple purines was simultaneously evaluated by ultra-sensitive HPLC-FLD methodologies.

Results: ATP, ADP, AMP, NAD+/ADPR and adenosine were detected intraluminally and extraluminally, suggesting that cells in the bladder mucosa and the suburothelium/lamina propria are likely exposed to a variety of purines during bladder filling. Since the amounts of detected purines at any particular time represent released minus removed purines, greater degradation likely occurs during the longer bladder filling with 200 µL fluid. Yet, higher purine amounts were generally detected, on both sides, at 200 µL filling volume. The rate of purine metabolism during different stages of bladder filling remains to be determined. The ratio of intraluminal to extraluminal content differed for individual purines. Thus, the intraluminal ATP was ~10-folds higher than the extraluminal ATP at both filling volumes, whereas the intraluminal NAD+ exceeded the extraluminal NAD+ ~5-folds and adenosine amounts were similar on both sides of the urothelium.

Conclusions: Multiple purines are released from both sides of the mucosa during bladder filling, possibly stimulating multiple cell type targets in the bladder wall. It remains to be determined whether intraluminally-released purines can be transported to the suburothelium or reach the detrusor smooth muscle. Further studies are warranted to understand the mechanisms of mechanosensitive release, transport and metabolism of purines in the bladder wall and the role of these purines in regulating bladder functions during the micturition cycle.

Funding Source(s): NIH grant DK 41315

Keywords: Bladder; urothelium; purinergic; sensory; ex vivo