Ontogeny of the Na(+)-H+ exchanger in rat ileal basolateral membrane vesicles.
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 pHi/pHo = 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 Km for amiloride-sensitive Na+ uptake of 12.6 +/- 6.6, 10.2 +/- 1.77, 9.46 and Vmax 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.(ABSTRACT TRUNCATED AT 250 WORDS)
Daher
M
M
Department of Pediatric Gastroenterology, Vanderbilt University Medical Center, Nashville, Tennessee 37232.
Acra
S
S
Ghishan
F K
FK
D000375:Aging / Q000502:physiology*; D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D000833:Animals, Suckling; D001693:Biological Transport, Active; D002352:Carrier Proteins / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D007082:Ileum / Q000201:enzymology / Q000254:growth & development / Q000502:physiology*; D007700:Kinetics; D008564:Membrane Potentials; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers; D000254:Sodium-Potassium-Exchanging ATPase / Q000032:analysis; D014886:Weaning
D002352:Carrier Proteins; D017923:Sodium-Hydrogen Exchangers; D000584:Amiloride; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase