In vitro modulation of L-arginine transport in trophoblast cells by glucose

BACKGROUND: The uptake of the semi-essential amino acid, L-arginine, into trophoblast cells was measured with the aim of determining the effect of different glucose concentrations on L-arginine influx kinetics. METHODS: This study used a novel superfused microcarrier culture system of BeWo cells (an established choriocarcinoma cell line with many characteristics of normal human trophoblast) and a rapid, paired-tracer dilution technique to measure unidirectional influx into the cells. RESULTS: At 10 mmol L-1 D-glucose, L-arginine unidirectional influx across the microvillous border of the cells was saturable with a Km of 1.14 +/- 0.14 mmol L-1 and a Vmax of 121. 36 +/- 5.89 nmol mg-1 protein min-1. When cells were preincubated for 24 h in the presence of 30 mmol L-1 D-glucose, there was a significant increase in the Vmax for L-arginine of nearly 30%. Similarly, preincubation in the presence of 1 mmol L-1 D-glucose and 12.5 mIU mL-1 human insulin reduced the Km for L-arginine influx by over 55%. CONCLUSION: These data suggest that the modulation of placental transport of L-arginine by glucose and insulin could contribute to the fetal macrosomia observed in diabetic mothers.