Otogeny of sugar transport in fetal rat kidney.

Concentration of alpha-methyl-D-glucopyranoside (alpha-MG) by kidney slices of rat fetuses increases during the studied period of gestation from day 18 until day 21 (last day of gestation). Glucoside transport is inhibited by phloridzin, D-glucose and D-galactose. Concentration dependence, over a substrate range from 0.01 to 0.2 mM, was studied on day 21: alpha-MG transport obeys a saturation kinetic with a low apparent Km (0.22 mM); D-glucose inhibition is of competitive nature (apparent Ki: 0.47 mM). Sodium dependence is demonstrated on day 21 of gestation: the phloridzine-sensitive transport, entirely inhibited in Na+-free medium, is enhanced when medium Na+ concentration increases from 0 to 143 mEq/l (Krebs-Ringer buffer concentration); further increase of Na+ concentration has no effect.