The cholinergic and purinergic components of detrusor contractility in a whole rabbit bladder model

Whole rabbit bladders were suspended in a bath chamber and stimulated with ATP, bethanechol, electrical field stimulation, and bethanechol + ATP. Detrusor pressure and fluid expelled by the bladder were recorded, synchronized, and digitized. Detrusor work and power were calculated with a computer program. Maximum work was 61.4 +/- 28.7, 83.3 +/- 17.0, 85.0 +/- 15.0, 90.8 +/- 13.1 cm. H2O, ml. for ATP, bethanechol, electrical and bethanechol + ATP, respectively. Maximum power generated by ATP was 4.8 +/- 3.0 cm. H2O, ml./sec and was approximately 66% of that generated by bethanechol, and 50% of that generated by electrical stimulation, and bethanechol + ATP. ATP cannot empty the bladder with moderate outlet resistance while bethanechol and electrical stimulation can. Our results suggest that ATP is able to generate detrusor power and achieve work in bladder emptying. However, ATP generated power and work is considerably less than that of electrical stimulation or bethanechol alone. ATP mediated contraction is not inhibited by atropine or tetrodotoxin but is inhibited by P2 purinoceptor desensitization, suggesting a functional role of purine receptors on detrusor smooth muscle. Since ATP generated pressure is more rapid than with bethanechol alone, we support the hypothesis that ATP may be important in the initiation of micturition.