Influence of hypo-osmolality on the activity of short-chain neutral amino acid carriers in trout (Salmo trutta) red blood cells.

Abstract

The present study shows that in trout red blood cells the activity of some amino acid carriers, not directly involved in cell volume regulation, is affected by external osmolality. Glycine uptake has been used as the experimental approach because it was shown previously that it is effected by different carriers, namely the Na+-dependent ASC and Gly systems, as well as the Na+-independent asc and L systems. An increase in the uptake through the Gly system and the two Na+-independent carriers was found, while the ASC system appeared to be downregulated. Those systems whose activities were increased by hypo-osmolality did not share the mechanism by which this increase was obtained. Thus, the Gly system was sensitive to intracellular ionic changes, while the Na+- independent systems were mechanically stimulated, as assessed by the iso-osmotic swelling caused by ammonium chloride. On the other hand, a volume-sensitive transporter may be present in trout red blood cells, which is involved in the swelling-induced glycine movement, as can be deduced from the effect of some inhibitors such as pyridoxal phosphate, DIDS (4,4'-diisothiocyanate-stilbene-2,2'-disulfonic acid) and quinine.