Effect of trypan blue on the action of acetylcholine, histamine and salbutamol in the isolated guinea-pig ileum.
It has been reported that trypan blue, a diazo dye with polyamphipatic structure, can inhibit the coupling of receptors to G-proteins. This inhibition of G-protein coupling has been investigated in isolated guinea-pig ileum. It was found that trypan blue could elicit a slight but dose-dependent contractile response in isolated guinea-pig ileum (4.5% of maximum contractile response induced by acetylcholine). While trypan blue potentiated the effect of histamine and shifted its dose-response curve to the left, it did not affect the contractile effects of acetylcholine. Furthermore, the relaxation which has been induced by salbutamol, a beta 2 agonist, was inhibited by trypan blue. It is concluded that trypan blue, as shown in biochemical studies, act selectively and can uncouple Gs-protein from beta 1 receptors. However, the effect of trypan blue on the whole tissue preparation depends on the type of G-protein involved and post G-protein processes which are stimulated after receptor activation. Trypan blue and similar agents could provide useful tools for further investigations of the mechanism of receptor-G protein coupling in the whole tissue preparation.
Mahmoudian
M
M
Department of Pharmacology, Iran University of Medical Sciences, Tehran.
Damankeshideh
M
M
D000109:Acetylcholine / Q000378:metabolism / Q000494:pharmacology; D000318:Adrenergic beta-Agonists / Q000378:metabolism / Q000494:pharmacology*; D000420:Albuterol / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D004396:Coloring Agents / Q000633:toxicity*; D004305:Dose-Response Relationship, Drug; D019204:GTP-Binding Proteins / Q000378:metabolism; D006168:Guinea Pigs; D006632:Histamine / Q000378:metabolism / Q000494:pharmacology; D007082:Ileum / Q000187:drug effects* / Q000378:metabolism; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects*; D014343:Trypan Blue / Q000633:toxicity*; D014475:Uncoupling Agents / Q000633:toxicity
D000318:Adrenergic beta-Agonists; D004396:Coloring Agents; D014475:Uncoupling Agents; D006632:Histamine; D019204:GTP-Binding Proteins; D014343:Trypan Blue; D000109:Acetylcholine; D000420:Albuterol