Non-Michaelis-Menten kinetics of zero-trans glucose uptake by trophoblast cells from human term placentae and by choriocarcinoma (JEG-3/JAR) cells.

Maternal glucose is a major substrate for placental and fetal metabolism. The kinetics of its uptake into placental trophoblast cells has not been characterised yet and was therefore investigated in the present study. In addition to trophoblast cells isolated from human term placentae, JEG-3 and JAR choriocarcinoma cells were used. Measurements were carried out in 5 s intervals until 30 s with the non-metabolisable glucose analogue 3-O-[14C]methyl-D-glucose using confluent cells adhering to glass coverslips. L-[1-14C]glucose was used to correct for extracellular trapped tracer and diffusion. The uptake was rapid and saturable. It reached equilibrium after 30 s at 20 degrees C and could be inhibited by 0.4 mmol/l cytochalasin B up to 98%. The choriocarcinoma cells took up twice as much glucose as trophoblast cells. Fitting the experimental data to the Michaelis-Menten equation by non-linear regression failed to adequately describe the data, even when a contribution of diffusion to total uptake was considered. Introducing the Hill coefficient n into the Michaelis-Menten equation significantly improved the quality of the fits as was assessed by three statistical criteria. Using this equation modified for allosteric kinetics (v = k[To] [S]n)/(Km + [S]n)), parameters were calculated as Km = 12 mmol/l, Vmax = 17 fmol/l s-1 per cell, n = 1.1 for trophoblast cells; Km = 13 mmol/l, Vmax = 27 fmol/l s-1 per cell, n = 1.2 for JEG-3 cells and Km = 29 mmol/l, Vmax = fmol/l s-1 per cell, n = 1.4 for JAR cells.(ABSTRACT TRUNCATED AT 250 WORDS)