Characterisation of Amino Acid transport in Red Blood Cells of a Primitive Vertebrate, the Pacific Hagfish (Eptatretus Stouti)

Abstract

ABSTRACT Intracellular amino acid levels and the characteristics of amino acid transport were investigated in red blood cells of a primitive vertebrate, the Pacific hagfish (Eptatretus stouti Lockington). In contrast to red cells from euryhaline teleosts and elasmobranchs, which contain high concentrations of β-amino acids, those from hagfish exhibited an intracellular amino acid pool (approx. 100 mmol l−1 cell water) composed almost entirely of conventional α-amino acids. Red celkplasma distribution ratios for individual amino acids ranged from 219, 203 and 173 for alanine, α-amino-n-butyrate and proline, respectively, to 11 and 13 for lysine and arginine. Corresponding distribution ratios for Na+, K+ and Cl− were 0.043, 21 and 0.32, respectively. The cellular uptake of amino acids, with the exception of L-proline and glycine, was Na+-independent. Compared with mammalian and avian red cells, those from hagfish exhibited 104-fold higher rates of L-alanine transport. Uptake of this amino acid from the extracellular medium was concentrative, but occurred as a 1:1 exchange with intracellular amino acids. The L-alanine transport mechanism was identified as an asc type system on the basis of its Na+-independence and selectivity for neutral amino acids of intermediate size. A volume-sensitive amino acid channel, which is found in both euryhaline teleosts and in elasmobranchs, is absent from hagfish red cells.