Electrically Stimulated Relaxation is not Mediated by GABA in Cat Lower Esophageal Sphincter Muscle

  • Park Sun-Young (Department of Pharmacology, College of Pharmacy, Chung Ang University) ;
  • Shin Chang-Yell (Department of Pharmacology, College of Pharmacy, Chung Ang University) ;
  • Song Hyun-Ju (Department of Pharmacology, College of Pharmacy, Chung Ang University) ;
  • Min Young-Sil (Department of Pharmacology, College of Pharmacy, Chung Ang University) ;
  • La Hyen-O (Department of Pharmacology, College of Medicine, The Catholic University of Korea) ;
  • Lee Jun-Woo (Department of Pharmacology, College of Pharmacy, Chung Ang University) ;
  • Kim Do-Young (Department of Pharmacology, College of Pharmacy, Chung Ang University) ;
  • Je Hyun-Dong (Department of Pharmacology, College of Pharmacy, Catholic University of Daegu) ;
  • Sohn Uy-Dong (Department of Pharmacology, College of Pharmacy, Chung Ang University)
  • Published : 2006.05.01

Abstract

This study examined the effect of Gamma-Amino butyric acid (GABA) and selective GABA receptor related drugs on the electrically stimulated relaxation in the lower esophageal sphincter muscle (LES) of a cat. Tetrodotoxin $(10^{-6}\;M)$ suppressed the electrically stimulated (0.5-5 Hz) relaxation of the LES. However, guanethidine $(10^{-6}\;M)$ and atropine $(10^{-6}\;M)$ had no effect indicating that the relaxations were neurally mediated via the nonadrenergic and noncholinergic (NANC) pathways. NG-nitro-L-arginine methyl ester ($10^{-4}M$, L-NAME) also inhibited the relaxant response but did not completely abolish the electrically stimulated relaxation with 60% inhibition, which suggests the involvement of nitric oxide as an inhibitory transmitter. This study examined the role of GABA, an inhibitory neurotransmitter, on neurally mediated LES relaxation. GABA ($10^{-3}-10^{-5}M$, non selective receptor agonist), muscimol ($10^{-3}-10^{-5}M$, GABA-A agonist), and baclofen ($10^{-3}-10^{-5}M$, GABA-B agonist) had no significant effect on the electrically stimulated relaxation. Moreover, bicuculline ($10^{-5}M$, GABA-A antagonist) and phaclofen ($10^{-5}M$, GABA-B antagonist) had no inhibitory effect on the electrically stimulated relaxation. This suggests that GABA and the GABA receptor are not involved in the electrically stimulated NANC relaxation in the cat LES.

Keywords

References

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