ONTOGENY OF NA+ D-GLUCOSE COTRANSPORT IN GUINEA-PIG JEJUNAL VESICLES - ONLY ONE SYSTEM IS INVOLVED AT BOTH 20-DEGREES-C AND 35-DEGREES-C/

The kinetic parameters of Na+/D-glucose cotransport were examined in f etal, newborn and adult guinea-pig jejunal brush-border membrane vesic les using a displacement curve and non-linear regression procedure. Ou r data indicated the presence of a single system with a K-m of 0.34 +/ - 0.04 mM at both 20 degrees C and 35 degrees C. V-max was increased b y about 4-fold when the kinetic experiments were performed at 35 degre es C. Since our results were not in agreement with the findings of Bro t-Laroche et al. (J. Biol. Chem. (1986) 261, 6168-6176) which indicate d the existence of a distinct D-glucose transport system in the adult guinea-pig jejunum at 35 degrees C, we verified the influence of their experimental conditions on initial rate uptake measurements. In the p resence of D-sorbitol instead of D-mannitol in the transport media, 70 % inhibition of D-glucose uptake was observed, an effect which was att ributable to contamination of sorbitol preparations by D-glucose. Afte r removal of glucose contamination D-sorbitol did not significantly re duce the initial rate of D-glucose transport. These results led us to conclude the existence of a single D-glucose transport system in the g uinea-pig small intestine and to stress the choice of experimental con ditions as being crucial for an accurate estimation of kinetic paramet ers.