This study was designed to examine the activity of the Na+-H+ exchanger across the basolateral membranes of the ileal enterocyte and its developmental pattern. The function of the Na+-H+ exchanger was studied using a well validated basolateral membrane vesicle technique. Na+ uptake represented transport into the vesicle rather than binding as validated by initial rate studies. Na+ uptake represented an electroneutral process as shown by studies in which negative membrane potential was induced by the ionophore valinomycin. Various outwardly directed pH gradients significantly stimulated Na+ uptake compared with no pH gradient conditions at all age groups. However, the magnitude of stimulation was significantly different between the age groups with more marked stimulation of amiloride-sensitive Na+ uptake occurring in adolescent rats as compared to weanling or suckling rats. The amiloride sensitivity of the pH stimulated Na+ uptake was investigated using [Amiloride] = 10-2-10-5 M at pH(i)/pH(o), = 5.2/7.5. At 10-2 M amiloride concentration, Na+ uptake was inhibited by 80%, 70%, 77%, in the basolateral membranes of adolescent, weanling and suckling rats, respectively. Dixon plot analysis in both adolescent and weanling rats was consistent with two amiloride binding sites, a low affinity system and a high affinity system. In the suckling rat, on the other hand, the data supported a single high affinity binding site. Kinetic studies revealed a K(m) for amiloride-sensitive Na+ uptake of 12.6 ± 6.6, 10.2 ± 1.77, 9.46 and V(max) of 4.83 ± 1.22, 4.47 ± 0.36 and 8.08 ± 1.92 n.mol.mg.protein-1.7 s-1 in suckling, weanling and adolescent rats, respectively. There were no statistically significant differences between the K(m) values of the different age groups. However, V(max) in adolescent rats was significantly greater than those of younger rats. These findings suggest, for the first time, the presence of an ileal basolateral membrane Na+-H+ antiporter system in the rat during development.
|Original language||English (US)|
|Number of pages||7|
|Journal||Journal of Developmental Physiology|
|State||Published - Oct 3 1991|
ASJC Scopus subject areas
- Developmental Biology