Taurocholate transport by brush-border membrane vesicles from the developing rabbit ileum: structure/function relationships.
To examine the ontogenesis of bile acid transport in the rabbit ileum, brush-border membrane vesicles (12- to 20-fold purified) were prepared from 14- to 49-day-old animals. Taurocholate uptake was characterized by the emergence of secondary active, Na(+)-dependent transport at the start of weaning (21 days). Transient intravesicular accumulation (overshoot) of taurocholate occurred at 5-10 s of incubation, and the overshoot maximum increased significantly from 21 days (349.2 +/- 22.4 nmol/mg protein) to 35 days (569.0 +/- 84.3 nmol/mg protein; p less than 0.001), without further increase at maturity (49 days, not equal to 607.6 +/- 136.7 nmol/mg protein). No significant taurocholate active uptake component was noted at 14 days; however, ileal vesicles from sucklings showed carrier-mediated, Na+ D-glucose cotransport. In greater than or equal to 35-day-old rabbits, osmolarity studies at 20 s of incubation showed that only approximately 12% of [14C]taurocholate uptake was secondary to bile acid-to-membrane binding. Conversely, at 20 min, greater than 95% of radiolabel incorporation represented solute bound to the external and/or internal membrane surface. Arrhenius plots establish brush-border membrane taurocholate uptake as an intrinsic, lipid-dependent process, with a slope discontinuity between 24 and 28 degrees C, similar to the membrane lipid thermotropic transition region. Steady-state fluorescence polarization studies (1,6-diphenyl-1,3,5-hexatriene) demonstrate a temporal association between the maturation of taurocholate uptake and age-related decreases in ileal brush-border membrane fluidity. These data indicate that maturation of bile acid secondary active transport in the rabbit ileum may be regulated, at least in part, by changes in brush-border membrane lipid dynamics.
Schwarz
S M
SM
Department of Pediatrics, New York Medical College, Valhalla 10595.
Watkins
J B
JB
Ling
S C
SC
D000367:Age Factors; D000818:Animals; D000833:Animals, Suckling / Q000254:growth & development; D001693:Biological Transport, Active; D002250:Carbon Radioisotopes; D002462:Cell Membrane / Q000378:metabolism*; D004764:Enterohepatic Circulation; D007082:Ileum / Q000254:growth & development* / Q000378:metabolism; D066298:In Vitro Techniques; D007413:Intestinal Mucosa / Q000166:cytology / Q000378:metabolism; D008297:Male; D008560:Membrane Fluidity; D008871:Microvilli / Q000378:metabolism; D051381:Rats; D013656:Taurocholic Acid / Q000378:metabolism*; D014886:Weaning
D002250:Carbon Radioisotopes; D013656:Taurocholic Acid