Regulatory characteristics of amino acid transport in newborn rat renal cortex cells

The uptake of α-aminoisobutyric acid by slices of kidney cortex from newborn rats is enhanced by a preliminary incubation of the tissue in buffer at 37 °C. This effect is abolished by anaerobiosis, the presence of dinitrophenol or the removal of Na⁺ during the preliminary incubation. Cycloheximide (50 μM) and purimycin (1 mM) as well as α-aminoisobutyric acid, glycine and proline (5 mM) in the pre- incubation buffer also abolish the effect, while actinomycin D (0.8 μM) partially inhibits the enhancement due to preliminary incubation. A kinetic examination of the phenomenon indicates that the enhanced uptake is due to an increased entry rate into the cells without a change in efflux. There is no alteration in the apparent transport $\text{K}{}_{\mathrm{<mtext>m</mtext>}}$ but an increase in the $\text{V}$ for entry. The effect is dependent on tissue age being observed between birth and 22 days, after which there is a decrease in response to preliminary incubation with no effect seen in adult tissues.