Calcium transport by basal lateral membrane vesicles from rat small intestine decreases with age.
There is a marked decrease in active Ca2+ transport by the rat small intestine with age, particularly between 2 and 12 months. Much evidence suggests that the active component of Ca2+ transport resides in the energy-dependent pumping of Ca2+ across the intestinal basal lateral membrane. Therefore, we have characterized Ca2+ uptake by basal lateral membrane vesicles isolated from young (2-3 month old) and adult (12-14 month old) rats. In vesicles from the proximal duodenum, ATP-dependent Ca2+ uptake was about 4-times greater in the young animal than in the adult. There were no age differences in Ca2+ uptake in the absence of ATP. In vesicles from the ileum, Ca2+ uptake was much less than in the duodenum. The age differences in the ileum were smaller, and ATP-dependent Ca2+ uptake in the young was only twice that seen in the adult. Osmotic lysis of duodenal vesicles reduced Ca2+ uptake to low levels in both age groups, indicating that most of the Ca2+ was being taken up into an osmotically active space. Kinetic studies of Ca2+ uptake showed that there was no change in the apparent affinity but a 5-fold decrease in the Vmax of the adult Ca2+ transport system compared to that of the young animal. This marked decrease in the capacity of basal lateral membrane vesicles to actively transport Ca2+ may contribute to the decline in intestinal Ca2+ absorption with age.
Armbrecht
H J
HJ
Geriatric Research, Education and Clinical Center, St. Louis Veterans Administration Medical Center, MO 63125.
Doubek
W G
WG
Porter
S B
SB
D000375:Aging; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism*; D002474:Cell-Free System; D004386:Duodenum / Q000378:metabolism; D004848:Epithelium / Q000378:metabolism; D007082:Ileum / Q000378:metabolism; D066298:In Vitro Techniques; D007421:Intestine, Small / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D009840:Oligomycins / Q000494:pharmacology; D051381:Rats; D011916:Rats, Inbred F344; D014639:Vanadium / Q000494:pharmacology
D002135:Calcium-Binding Proteins; D009840:Oligomycins; D014639:Vanadium; D002118:Calcium