BACKGROUND AND PURPOSE
To characterise the molecular mechanisms that determine variability of atropine-resistance of nerve-mediated contractions in human and guinea-pig detrusor smooth muscle
Atropine-resistance of nerve-mediated contractions, and the role of P2X1 receptors, was measured in isolated preparations from guinea-pigs and also humans with or without overactive bladder syndrome, from which the mucosa was removed. Nerve-mediated ATP release was measured directly with amperometric ATP-sensitive electrodes. Ecto-ATPase activity of guinea-pig and human detrusor samples was measured in vitro by measuring the concentration-dependent rate of ATP breakdown. The transcription of ecto-ATPase subtypes in human samples was measured by qPCR.
Atropine resistance was greatest in guinea-pig detrusor, absent in human tissue from normally-functioning bladders and intermediate in human overactive bladder. Greater atropine resistance correlated with reduction of contractions by the ATP-diphospho-hydrolase apyrase, directly implicating ATP in their generation. E-NTPDase-1 was the most abundantly transcribed ecto-ATPase of those tested and transcription was reduced in tissue from human overactive, compared to normal, bladders. E-NTPDase-1 enzymatic activity was inversely related to the magnitude of atropine resistance. Nerve-mediated ATP release was continually measured and varied with stimulation frequency over the range 1-16 Hz.
CONCLUSION AND IMPLICATIONS
Atropine-resistance in nerve-mediated detrusor contractions is due to ATP release and its magnitude is inversely related to E-NTPDase-1 activity. ATP is released under different stimulation conditions compared to acetylcholine that implies different routes for their release.