Amino acid transport by the cultured human placental trophoblast: effect of insulin on AIB transport.
Insulin responsiveness in the human placenta is controversial. This study evaluated insulin stimulation of alpha-aminoisobutyric acid (AIB) uptake in cultured human placental trophoblasts. Both Na(+)-dependent and -independent components of AIB uptake were present in cultured trophoblasts. Na(+)-dependent AIB uptake was significantly stimulated by insulin in a time-dependent manner, as early as 2 h, with a maximum at 12 h of continuous exposure to hormone. Insulin treatment for 4 h increased both the initial uptake rate and the final intracellular concentration. Stimulation was dependent on insulin concentration, with significant stimulation beginning at 10(-9) M. Insulin treatment increased maximum velocity but not the Michaelis constant. Approximately 75% of basal (unstimulated) AIB uptake was inhibited by 10 mM alpha-methylaminoisobutyric acid (MeAIB). The insulin-stimulated increment above basal AIB uptake was completely inhibited by 10 mM MeAIB. Cycloheximide treatment significantly reduced basal and stimulated AIB uptake, although a significant response to insulin persisted. Na(+)-dependent AIB uptake was also stimulated by glucagon, dexamethasone, and 8-bromoadenosine 3',5'-cyclic monophosphate, but not by vasopressin. This study further characterizes amino acid uptake by the human placenta and demonstrates that the Na(+)-dependent component of AIB uptake by the cultured trophoblasts is stimulated by physiological concentrations of insulin.
Karl
P I
PI
Department of Pediatrics, North Shore University Hospital-Cornell University Medical College, Manhasset, New York 11030.
Alpy
K L
KL
Fisher
S E
SE
D000596:Amino Acids / Q000493:pharmacokinetics*; D000621:Aminoisobutyric Acids / Q000493:pharmacokinetics* / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D002454:Cell Differentiation; D002478:Cells, Cultured; D003513:Cycloheximide / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D006801:Humans; D007328:Insulin / Q000494:pharmacology*; D009994:Osmolar Concentration; D010920:Placenta / Q000166:cytology / Q000378:metabolism*; D013997:Time Factors; D014327:Trophoblasts / Q000378:metabolism*
D000596:Amino Acids; D000621:Aminoisobutyric Acids; D007328:Insulin; C100049:2-aminoisobutyric acid; C017911:2-(methylamino)isobutyric acid; D003513:Cycloheximide