The membrane permeability of nonelectrolytes and carbohydrate metabolism of Amazon fish red cells

Abstract

The membrane permeability to nonelectrolytes and carbohydrate metabolism were examined in red cells obtained from the Amazon fishes including the electric eel (Electrophorus electrocus), the arawana (Osteoglossum bicirrhosum), the pirarucu (Arapaima gigas), the lungfish (Lepidosireti paradoxa), and the armored catfish (Pterygoplichthys). Glucose permeability was fastest in the electric eel, followed by the lungfish. The red cells of the arawana were only slightly permeable to glucose. Both the armored catfish and the pirarucu red cells were found to be totally impermeable to glucose. There was no evidence for the presence of the facilitated diffusion mechanism for glucose transport in any of these fish red cells. In sharp contrast with glucose, red cells of all five species were quite permeable to ribose and urea. Urea permeability of red cells decreased in order of magnitude with the lungfish > the electric eel > the arawana > the armored catfish [Formula: see text] the pirarucu. The urea permeability of the lungfish was inhibited in the presence of phloretin.Of the two metabolic substrates, glucose but not ribose was metabolized to lactate with a concomitant contribution to ATP maintenance by the lungfish red cells. Even though the glucose-impervious pirarucu cells could not utilize glucose, ribose was readily metabolized by the pirarucu cells.