Interactions between heavy metal chelators and botulinum neurotoxins at the mouse neuromuscular junction

• Published in: Toxicon (Oxford) 1995-04, Vol.33 (4), p.539-549
• Main Authors: Sheridan, Robert E., Deshpande, Sharad S.
• Format: Article
• Language: English
• Subjects: Animals; Bacteriology; Biological and medical sciences; Botulinum Toxins - pharmacology; botulism; chelating agents; Chelating Agents - pharmacology; chelation; Clostridium botulinum; diaphragm; Diaphragm - drug effects; Diaphragm - innervation; foodborne illness; Fundamental and applied biological sciences. Psychology; in vitro; In Vitro Techniques; Male; mechanism of action; Mice; Microbiology; Muscle Contraction - drug effects; muscles; Neuromuscular Junction - drug effects; neurotoxins; paralysis; Pathogenicity, virulence, toxins, bacteriocins, pyrogens, host-bacteria relations, miscellaneous strains; Phrenic Nerve - drug effects; rats; Respiratory Paralysis - chemically induced; Respiratory Paralysis - physiopathology; Synaptic Transmission - drug effects; zinc; Zinc - pharmacology
• ISSN: 0041-0101; 1879-3150
• DOI: 10.1016/0041-0101(94)00185-B

Exposure of isolated mouse hemidiaphragms to botulinum neurotoxins, 0.1 nM BoNT-A or BoNT-B, at 36 °C reduced nerveelicited peak isometric twitch tension to 50% of control values at 55 min (BoNT-A) to 68 min (BoNT-B) after application. Either coincubation of BoNT with the heavy metal chelator TPEN, preincubation with TPEN followed by BoNT, or application of TPEN after BoNT but before neuromuscular block, delayed the onset of muscle failure in a dose-dependent manner by up to five-fold. TPEN doses between 2 and 10 μM were required to antagonize significantly the muscle block produced by BoNT, and the delay in onset was maximal between 10 and 50 μM TPEN. Treatment of muscles with a Zn 2+-TPEN coordination complex, rather than TPEN alone, eliminated any beneficial effects of TPEN on BoNT intoxication, indicating that these effects were mediated by chelation of Zn 2+. Other metal chelators that were not as membrane permeant as TPEN were ineffective in delaying BoNT paralysis, suggesting that TPEN acts by chelating intraterminal Zn 2+. In the absence of BoNT, TPEN caused a dose-dependent increase in nerve-elicited twitch tension with a half-maximal concentration at 8 μM. There was no corresponding change in twitches from direct electrical stimulation of the muscle. After BoNT (A or B serotype) had reduced the muscle twitch by 20 to 70%, however, subsequent application of TPEN rapidly depressed nerve-elicited twitches. The shift from potentiation to depression after BoNT treatment suggests that presynaptic vesicle mobilization and/or release involve Zn 2+-dependent enzymes and that BoNTs interact with these enzyme pathways.