Title Page Excitatory cholinergic and purinergic signalling in bladder are equally susceptible to botulinum neurotoxin A consistent with co-release of transmitters from efferent fibres

Mediators of neuromuscular transmission in rat bladder strips were dissected pharmacologically to examine their susceptibilities to inhibition by botulinum neurotoxins (BoNTs) and elucidate a basis for the clinical effectiveness of type A in alleviating smooth muscle spasms associated with over-active bladder. BoNT/A, /C1 or /E reduced peak and average force of muscle contractions induced by electric field stimulation (EFS) in dose-dependent manners by acting only on neurogenic, tetrodotoxin-sensitive responses. BoNTs that cleave vesicle-associated membrane protein (VAMP) proved much less effective. Acetylcholine and ATP were found to provide virtually all excitatory input because EFS-evoked contractions were abolished by the muscarinic receptor antagonist, atropine, combined with either a desensitising agonist of P2X1 and P2X3 or a non-selective ATP-receptor antagonist. Both transmitters were released in the innervated muscle layer and, thus, persisted after removal of urothelium. Neither atropine nor a desensitiser of the P2X1 or P2X3 receptors altered the rate at which muscle contractions were weakened by BoNT/A. Moreover, though cholinergic and purinergic signalling could be partially delineated using high frequency EFS (which intensified a transient, largely atropine-resistant, spike in muscle contractions that was reduced following P2X-receptor desensitisation), they proved equally susceptible to BoNT/A. Thus, equi-potent blockade of ATP co-released with acetylcholine from muscle efferents likely contributes to the effectiveness of BoNT/A in treating bladder over-activity, including non-responders to anti-cholinergic drugs. As purinergic receptors are known mediators of sensory afferent excitation, inhibition of efferent ATP release by BoNT/A could also help to ameliorate acute pain and urgency sensation reported by some recipients. This article has not been copyedited and formatted. The final version may differ from this version. JPET Fast Forward. Published on June 24, 2010 as DOI: 10.1124/jpet.110.169342 at A PE T Jornals on A ril 9, 2017 jpet.asjournals.org D ow nladed from