title: Amethocaine-induced inhibition of mitochondrial monoamine oxidase activity.
abstract: Amethocaine (tetracaine) (1-10 microM) produces a concentration-dependent in-vitro inhibition of mitochondrial membrane-bound MAO activity towards tyramine (18-84% in brain and 19-84% in liver) and 5-hydroxytryptamine (5-HT) (23-94% in brain and 20-100% in liver). At relatively higher concentrations (25-300 microM) of amethocaine, benzylamine oxidation is inhibited in brain (24-91%) and liver (29-100%). The extent of MAO inhibition is appreciably reduced when preincubation time of the enzyme with a low concentration (7.5 microM) of amethocaine is increased from zero to 45 min. This inhibition is reversible. The Km of MAO for tyramine is increased in brain (106-473%) and liver (121-352%) in the presence of amethocaine (2-7.5 microM) accompanied by a decrease in Vmax (21-51% in brain and 18-57% in liver). Similarly the Km of MAO for 5-HT is increased to the extent of 79-336% in brain and 51-225% in liver and the corresponding Vmax is decreased by 35-55% and 39-74%, respectively, in the presence of 2-5 microM amethocaine. At relatively higher concentrations (25-100 microM), amethocaine increases the Km of MAO for benzylamine in brain (25-101%) and liver (26-85%) and decreases the Vmax by 28-64% and 32-63% in the respective tissues. Thus these results suggest that amethocaine preferentially inhibits MAO-A and the nature of inhibition is reversible and of mixed type.
mesh_terms: D000818:Animals; D001921:Brain / Q000201:enzymology; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D008928:Mitochondria / Q000201:enzymology*; D008930:Mitochondria, Liver / Q000201:enzymology; D008996:Monoamine Oxidase Inhibitors; D011506:Proteins / Q000378:metabolism; D051381:Rats; D013748:Tetracaine / Q000494:pharmacology*
chemical_list: D008996:Monoamine Oxidase Inhibitors; D011506:Proteins; D013748:Tetracaine