Electrically stimulated relaxation is not mediated by GABA in cat lower esophageal sphincter muscle.
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.
Park
Sun Young
SY
Department of Pharmacology, College of Pharmacy, Chung Ang University, Seoul 156-756, Korea.
Shin
Chang Yell
CY
Song
Hyun Ju
HJ
Min
Young Sil
YS
La Hyen
O
O
Lee
Jun Woo
JW
Kim
Do Young
DY
Je
Hyun Dong
HD
Sohn
Uy Dong
UD
D000818:Animals; D002415:Cats; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D049630:Esophageal Sphincter, Lower / Q000187:drug effects* / Q000201:enzymology / Q000294:innervation; D066298:In Vitro Techniques; D009126:Muscle Relaxation; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000378:metabolism; D009435:Synaptic Transmission; D013779:Tetrodotoxin / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
D004791:Enzyme Inhibitors; D013779:Tetrodotoxin; D005680:gamma-Aminobutyric Acid; D019001:Nitric Oxide Synthase; D019331:NG-Nitroarginine Methyl Ester