Excitatory cholinergic and purinergic signaling in bladder are equally susceptible to botulinum neurotoxin a consistent with co-release of transmitters from efferent fibers

• Published in: The Journal of pharmacology and experimental therapeutics 2010-09, Vol.334 (3), p.1080-1086
• Main Authors: Lawrence, Gary W, Aoki, K Roger, Dolly, J Oliver
• Format: Article
• Language: English
• Subjects: Adenosine Triphosphate - metabolism; Adenosine Triphosphate - physiology; Animals; Botulinum Toxins, Type A - pharmacology; Electric Stimulation; In Vitro Techniques; Muscle Contraction - drug effects; Muscle, Smooth - drug effects; Nerve Fibers - drug effects; Nerve Fibers - metabolism; Neurons, Efferent - drug effects; Neurons, Efferent - metabolism; Neurotransmitter Agents - metabolism; Parasympathetic Nervous System - physiology; Rats; Receptors, Purinergic - physiology; Signal Transduction - drug effects; Synaptosomal-Associated Protein 25 - physiology; Tetrodotoxin - pharmacology; Urinary Bladder - drug effects; Vesicle-Associated Membrane Protein 1 - antagonists & inhibitors; Vesicle-Associated Membrane Protein 1 - immunology
• ISSN: 0022-3565; 1521-0103
• DOI: 10.1124/jpet.110.169342

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 P2X(1) and P2X(3) 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 P2X(1) or P2X(3) 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.