Potentiation of GABAA-receptor-mediated responses by barbiturates in the guinea-pig ileum.
In the isolated ileum of the guinea-pig, gamma-aminobutyric acid (GABA) elicited both GABAA- and GABAB-receptor-mediated responses. Barbiturates significantly potentiated the GABAA receptor-induced contractions over the lower dose range of applied GABA (less than 50 microM), without affecting the GABAB-receptor-induced 'after-relaxation', their relative potencies being thiopentone (ThP) greater than pentobarbitone (PB) greater than barbitone (Bb) greater than phenobarbitone (PhB). Also, higher doses of ThP, PB and Bb elicited bicuculline- and picrotoxinin-sensitive GABA-like contractions. PB shifted the dose-response curve for GABA in the presence of bicuculline methochloride to the left without altering the slope or the dose ratio, and not only displaced the dose-response curve for GABA in the presence of picrotoxinin but also restored the slope and the maximum response towards that of the control GABA-induced response. These results further characterise the GABAA-receptor sites of the guinea-pig enteric nervous system, where GABA is evidently a neurotransmitter.
D000818:Animals; D001463:Barbiturates / Q000494:pharmacology*; D001640:Bicuculline / Q000494:pharmacology; D004347:Drug Interactions; D005260:Female; D006168:Guinea Pigs; D007082:Ileum / Q000187:drug effects; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009126:Muscle Relaxation / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects*; D010424:Pentobarbital / Q000494:pharmacology; D010852:Picrotoxin / Q000031:analogs & derivatives / Q000494:pharmacology; D011963:Receptors, GABA-A / Q000187:drug effects / Q000502:physiology*; D054830:Sesterterpenes
D001463:Barbiturates; D001640:Bicuculline; D010424:Pentobarbital; D010852:Picrotoxin; D011963:Receptors, GABA-A; D054830:Sesterterpenes; C022961:picrotoxinin