Abstract
A method to study the export of citric acid cycle intermediates from rat liver mitochondria supplied with various individual substrates or combinations of substrates was designed to focus on the role of mitochondria in anaplerosis and cataplerosis. Under most conditions malate, citrate, and aspartate were exported in far higher amounts than isocitrate and alpha-ketoglutarate. In the presence of pyruvate alone or pyruvate in combination with most other substrates, citrate export equaled or was only slightly less than malate export. This contrasts with pancreatic islet mitochondria where citrate export is unaffected by many substrates. Malate and succinate potentiated pyruvate-induced citrate export and succinate caused massive malate export from liver mitochondria. Heart mitochondria, which possess very little or no pyruvate carboxylase, unlike liver and pancreatic islet mitochondria, did not produce malate from pyruvate. Heart mitochondria produced malate, but not citrate, from succinate. The results indicate that liver mitochondria export a larger number of metabolites from a wider range of substrates than do islet or heart mitochondria. This may reflect the multiple roles of the liver in body metabolism versus the specialized roles of the islet cell and heart.
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