Purpose: We compared the potency of adenosine triphosphate (ATP) and its nonhydrolyzable analogue alpha,beta-methylene ATP for generating contractions in human detrusor smooth muscle from patients with a stable, unstable and obstructed bladders. The different ATP potencies were compared with the ecto-adenosine triphosphatase (ATPase) of these samples.
Materials and methods: Contractile experiments were done in vitro by superfusing samples with purines and dose-response curves were generated. Ecto-ATPase activity was measured from the rate of ATP hydrolysis sensitive to the ecto-ATPase inhibitor ARL 67156 with a luciferin-luciferase assay.
Results: ATP generated contractions with a mean EC50 of 933 microM. in tissue from stable bladders and was significantly more potent in tissue from unstable and obstructed bladders (EC50 141 and 172 microM., respectively). alpha,beta-methylene ATP was more potent in tissue from stable and unstable bladders (mean combined EC50 3 microM.). In guinea pig detrusor the mean EC50 for ATP and alpha,beta-methylene ATP was 138 and 5.5 microM., respectively. Mean total ATPase activity in unstable bladder biopsies plus or minus standard deviation was about 50% of that in stable bladder biopsies (2.54 +/- 1.50 versus 1.37 +/- 0.46 nmol. per second per mg. protein ). The ARL 67156 sensitive fraction was also significantly less in samples from unstable compared with stable bladders (mean 0.94 +/- 0.41 versus 0.36 +/- 0.26 nmol. per second mg. protein ).
Conclusions: The greater potency of ATP for generating contractions in detrusor from unstable bladders may be due to reduced extracellular hydrolysis, allowing purine greater access to detrusor smooth muscle. This finding may explain atropine resistant purine based contractions in detrusor from unstable bladders.