Substrate transport and utilization in fish erythrocytes.

In contrast to mammalian erythrocytes which fulfil their energy requirements via anaerobic glycolysis, fish erythrocytes obtain most of their energy aerobically via the Krebs cycle. This enables them to use various substrates, including monocarboxylic acids, glucose and amino acids. This review discusses the membrane permeability of these substrates, and their relative importance in the energy production of fish erythrocytes. Agnathans are characterized by a high permeability to all of the potential substrates, glucose, monocarboxylic and amino acids. In contrast, teleost erythrocytes are often characterized by low glucose permeability. It appears that monocarboxylic acids and certain amino acids such as glutamine may be more important in energy production of teleost erythrocytes than glucose.