Abstract
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 BoNT/A in alleviating smooth muscle spasms associated with overactive bladder. BoNT/A, BoNT/C1, or BoNT/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 cleaved vesicle-associated membrane protein proved to be much less effective. Acetylcholine (ACh) 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 desensitizing agonist of P2X1 and P2X3 or a nonselective ATP receptor antagonist. Both transmitters were released in the innervated muscle layer and, thus, persisted after removal of urothelium. Atropine or a desensitizer of the P2X1 or P2X3 receptors did not alter the rate at which muscle contractions were weakened by BoNT/A. Moreover, although cholinergic and purinergic signaling could be partially delineated by using high-frequency EFS (which intensified a transient, largely atropine-resistant spike in muscle contractions that was reduced after P2X receptor desensitization), they proved equally susceptible to BoNT/A. Thus, equi-potent blockade of ATP co-released with ACh from muscle efferents probably contributes to the effectiveness of BoNT/A in treating bladder overactivity, including nonresponders to anticholinergic drugs. Because 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.
Footnotes
This work was supported in part by Science Foundation Ireland [Research Professorship Award O3/RP1/B345] (to J.O.D.), a Program of Research in Third Level Institutions IV grant from the Higher Education Authority of Ireland for the Neuroscience section of Target-Driven Therapeutics and Theranostics; and a Basic Research Award from Allergan Inc. (Irvine, CA).
Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
doi:10.1124/jpet.110.169342.
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ABBREVIATIONS:
- BoNT
- botulinum neurotoxin
- αβMeATP
- α,β-methylene-adenosine-5′-triphosphate
- ACh
- acetylcholine
- EFS
- electric field stimulation
- NDO
- neurogenic detrusor overactivity
- OAB
- overactive bladder
- PPADS
- pyridoxal-5′-phosphate-6-azophenyl-2′,4′-disulphonic acid
- SNAP-25
- synaptosomal-associated protein of Mr 25k
- SV2
- synaptic vesicle protein 2
- TTX
- tetrodotoxin.
- Received April 16, 2010.
- Accepted June 23, 2010.
- Copyright © 2010 by The American Society for Pharmacology and Experimental Therapeutics
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