ATP evokes cholinergic contraction in the healthy, but not inflamed, intact rat urinary bladder

      Background: Over the past years increasing evidence suggesting an altered role of purinergic signaling during pathological conditions has been presented. Furthermore, there have been speculations regarding a possible link between purinergic and cholinergic functional mechanisms. In order to further investigate this, an “intact (whole) bladder” in vitro-setup has presently been employed. Aim: To elucidate the role of the urothelium and the functional link between purinergic and cholinergic signaling in the healthy and inflamed intact rat urinary bladder. Methods: Intact urinary bladders were excised from anesthetized rats; controls or cyclophosphamide-treated (100 mg/kg 60 h before the experiment to induce cystitis). Two catheters were inserted into the bladder for administration of substances and outflow, respectively. Collagenase I was used to denude the urothelium. Functional studies were conducted in an organ bath system. Agonists and antagonists could be administered both into the surrounding Krebs solution and intravesically (via the catheters). Results and Conclusions: When instilling ATP into the intact bladder, a contraction was observed (5.8 ± 0.9 mN; 1 mM; n = 19) which, interestingly, was significantly decreased in the presence of atropine (1 μM; 2.2 ± 0.6 mN, p < 0.01; n = 11). This difference was not observed neither in inflamed (2.8 ± 0.4 and 2.4 ± 0.1 mN; n = 3-8), nor in urothelium denuded bladders (3.0 ± 1.3 and 3.3 ± 2.0 mN; n = 4-8). This preliminary study shows the delicate interactions between the two transmitter systems, namely that ATP partly induces detrusor muscle contractions indirectly by stimulating the release of acetylcholine. Also, the urothelium seems to be involved in this cholinergic response, which appears to be diminished during inflammation.
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