Rat and human cardiac monoamine oxidase: a comparison with other tissues

Experiments were made to test the proposal that rat heart mitochondrial monoamine oxidase (MAO) differs from that in certain other organs. Using kynuramine as the substrate, cardiac MAO of rats was compared with that in the vas deferens and liver. While the relative proportions of type A and B MAO varied between the three tissues, the sensitivity of the MAO types to preferential inhibitors, mixed substrate interactions and apparent Km determinations failed to reveal differences. Human atria contained mostly type B MAO, but the properties of the A and B types were not radically different from those found in rat tissues. No clorgyline-resistant MAO activity was detected with kynuramine, either in the rat or human tissues. Differences in rat heart MAO seem to be exposed by some substrates but not others, such as kynuramine.