Effect of hyper or hypo-osmotic conditions on neutral amino acid uptake and oxidation in tissues of the crab Chasmagnathus granulata

We investigated the transport of ¹⁴C-methylaminoisobutyric acid (¹⁴C-MeAIB) and ¹⁴C-alanine oxidation in hepatopancreas and jaw muscle of Chasmagnathus granulata submitted to 24, 72, and 144 h of hypo- or hyperosmotic stress. While ¹⁴C-MeAIB uptake increased in jaw muscle and hepatopancreas from crabs submitted to hyperosmotic stress, it did not change in tissues from animals submitted to hypo-osmotic stress. Incubation of jaw muscle and hepatopancreas from control groups with 1 mM ouabain did not decrease ¹⁴C-MeAIB uptake. However, ouabain prevented ¹⁴C-MeAIB uptake in hepatopancreas at 24 h of hyperosmotic stress. In contrast, in jaw muscle from crabs submitted to the same conditions, ¹⁴C-MeAIB uptake was not prevented by ouabain in the incubation medium. Jaw muscle from the control group produced four times more ¹⁴CO₂ from ¹⁴C-alanine than the hepatopancreas. During hypo-osmotic stress, amino acid oxidation does not seem to be one of the pathways implicated in the decrease of the amino acid pools in hepatopancreas and jaw muscle. In contrast, during hyperosmotic stress the reduction in ¹⁴C-alanine oxidation appears to be one of the mechanisms involved in the increase of the amino acid pool in the hepatopancreas.