Figure 4.

A high outwardly directed substrate concentration gradient imposed by various intravesicular system L amino acid substrates shows trans-stimulation of [¹⁴C]l-serine uptake resulting in overshoot phenomena. A) Various system L amino acid substrates or analogs were preloaded during vesiculation into MVM vesicles, and [¹⁴C]l-serine uptake was measured by incubation in Na⁺-free extravesicular buffer compared with nonloaded (NL) vesicles. B) To control for nonselective uptake effects, l-proline, MeAIB, and the osmotic control mannitol were also included. Data are means + sem (n = 4–9 placentas).