Ontogeny of Na/H antiporter activity in rabbit renal brush border membrane vesicles.
The development of the Na/H antiporter was studied in renal brush border membrane vesicles (BBMV) from fetal and adult rabbits using isotopic and fluorescent techniques. The kinetics of the antiporter studied by 22Na+ uptake revealed that the Vmax was only 25% of that in the adult; however, the Km's for Na+ were not significantly different. These data were confirmed by a fluorescent assay using the pH-sensitive probe, acridine orange: the Vmax was significantly lower in the fetal BBMV. Conductive Na+ movement was estimated from amiloride-insensitive 22Na+ uptake and the rate of alkalinization induced by K+, an ion whose relative conductance was found to be similar to that of Na+. Although relative Na+ conductance was significantly greater in fetal BBMV, the lower Vmax in fetal vesicles could not be ascribed to this factor. Maternal administration of betamethasone (50 micrograms/kg intramuscularly) for 2 d before delivery significantly increased the Vmax of the antiporter to levels observed in the adult; Km was unaffected. Na/K ATPase activity increased fourfold after betamethasone, but the specific activities of four brush border marker enzymes and the kinetics of Na(+)-glucose cotransport were unchanged. These data indicate that there is a developmental increase in brush border Na/H exchange which is the result of an increase in the number and/or the turnover number of the carriers. Further, these data suggest that the postnatal increase in antiporter activity may be related to the surge in glucocorticoid concentration that occurs perinatally.
Beck
J C
JC
Department of Medicine, Mount Sinai School of Medicine, New York 10029.
Lipkowitz
M S
MS
Abramson
R G
RG
D000165:Acridine Orange / Q000737:chemistry; D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001623:Betamethasone / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007668:Kidney / Q000196:embryology* / Q000378:metabolism; D007700:Kinetics; D008871:Microvilli / Q000378:metabolism; D009004:Monosaccharide Transport Proteins / Q000378:metabolism; D011817:Rabbits; D017923:Sodium-Hydrogen Exchangers; D013347:Subcellular Fractions / Q000378:metabolism
D002352:Carrier Proteins; D009004:Monosaccharide Transport Proteins; D017923:Sodium-Hydrogen Exchangers; D000584:Amiloride; D001623:Betamethasone; D000165:Acridine Orange