Yonsei Med J.  2012 Sep;53(5):968-973.

A Direct Inhibitory Effect of Botulinum Toxin Type A on Antral Circular Muscle Contractility of Guinea Pig

• Park JH
• Choi E
• Park H
• Lee YH

Abstract

PURPOSE
Recent studies suggest new mechanisms of Botulinum toxin (BoNT) other than inhibiting acetylcholine (ACh) release from nerve terminals. The aim of this study was to determine whether other mechanisms for BoNT exist, so that it directly inhibits smooth muscle contraction.
MATERIALS AND METHODS
Guinea pig antral muscle strips were studied in vitro after 2 hours of exposure to Botulinum toxin type A (BoNT/A). Contractile responses to electric field stimulation (EFS), high K+ (60 mM) and ACh (100 microM) were evaluated 24 and 48 hours after antral intramuscular injection of BoNT/A or vehicle.
RESULTS
BoNT/A inhibited muscular contraction caused by high K+ and ACh. Contractile responses to low (1 & 4 Hz) and high (8 & 20 Hz) frequency EFS of antral muscle strips 24 and 48 hours after antral intramuscular injection of BoNT/A were significantly inhibited.
CONCLUSION
The ability of BoNT/A to directly inhibit antral muscular contractility suggests a new mechanism for the pharmacologic actions of BoNT-direct inhibition of muscular contraction.

Keyword

Botulinum toxin type A; electrical field stimulation; gastric antrum

MeSH Terms

Acetylcholine
Animals
Botulinum Toxins*
Botulinum Toxins, Type A*
Guinea Pigs*
Guinea*
In Vitro Techniques
Injections, Intramuscular
Muscle Contraction
Muscle, Smooth
Pharmacologic Actions
Pyloric Antrum
Acetylcholine
Botulinum Toxins
Botulinum Toxins, Type A
Pharmacologic Actions

Figure

• 

  Fig. 1 Effect of various concentrations of BoNT/A on muscular contractions to EFS. BoNT/A reduced the EFS-induced contraction in a concentration-dependent fashion. (A) Tension recordings from guinea pig antral muscle strips showing progressive loss of contractile force with increasing concentration of BoNT/A. (B) Contractions of muscle strips to EFS were inhibited most effectively by 10U/m of BoNT/A. EFS, electric field stimulation.

• 

  Fig. 2 Effect of BoNT/A on muscle contractions to high K+. BoNT/A 10 U significantly inhibited contractile response induced by High K+ (60 mM).

• 

  Fig. 3 Effect of L-NAME and BoNT/A on muscle contractions induced by EFS. The addition of L-NAME (100 µM) increased contractile responses to EFS (p>0.05). When L-NAME (100 µM) and BoNT/A (10 U) were both applied to the muscle strips, there was a slight decrease of in EFS-induced muscle contractions (EFS at 1, 4, 8, or 20 Hz; p>0.05). L-NAME, N-nitro-L-arginine methyl ester; EFS, electrical field stimulation.

• 

  Fig. 4 Effect of L-NAME and BoNT/A on muscular contractions to ACh. The addition of L-NAME (100 µM) increased (p>0.05) contractile responses to Ach (100 µM). However, when L-NAME (100 µM) and BoNT/A (10 U) were both applied to muscular strips, there was a significant decrease in muscle contraction in response to ACh (p<0.05). L-NAME, N-nitro-L-arginine methyl ester; ACh, acetylcholine.

• 

  Fig. 5 Contractile responses to EFS of antral muscle strips excised 24 and 48 hours after injection of BoNT/A. (A) At 24 hours after intragastric injection of BoNT/A (4 & 10 U), there was a significant decrease in muscular contraction in response to EFS (1, 4, 8, or 20 Hz; p<0.05). However, no significant difference was found between EFS-induced contractile responses in the presence of BoNT/A (4 and 10 U; p>0.05). (B) At 48 hours after injection of BoNT/A, overall contractile responses to EFS were slightly enhanced compared to 24 hours. Muscular contractions in response to EFS were significantly decreased (p<0.05). No significant difference existed between contractile responses to EFS in the presence of BoNT/A (4 or 10 U; p>0.05). EFS, electric field stimulation.

• 

  Fig. 6 Pathologic changes in antral muscle strips taken 24 and 48 hours after intragastric injection of 10 U BoNT/A. Intramuscular hemorrhage and infiltration of inflammatory cells were detected in the muscle strips taken 24 (A) and 48 (B) hours after injection of BoNT/A (H&E stain, A: ×400, B: ×100).

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