Kinetics of calcium transport in the hamster duodenum and ileum.
Dietary calcium is absorbed chiefly from the small intestine, and characteristics of the transport process differ depending on site. Because transport behavior is crucial to calcium homeostasis, we characterized kinetics of duodenal and ileal calcium transport in vivo in the hamster. We measured net calcium transport with 40Ca and flux into the animal (influx) with 45Ca over the concentration range of 0- 25 mM. Nonmediated transport was twice as great in duodenum as in ileum. Mediated transport showed Michaelis-Menten kinetics. Kt for mediated transport (4.3 mM) was the same in duodenum and ileum, whereas Vmax (mumol/h per g) was twice as great in ileum (290) as in duodenum (137). Thus, Kt defines similar carrier function at both sites, but Vmax suggests calcium transport capacity is doubled in ileum. The lower nonmediated transport in ileum limits secretion and the higher Vmax absorbs calcium at a greater rate, permitting the ileum to move luminal calcium against a concentration gradient more effectively than the duodenum. Thus, ileal calcium transport, by its site and functional characteristics, makes a crucial contribution to calcium homeostasis in the hamster.
D000818:Animals; D001665:Binding Sites; D001692:Biological Transport; D002136:Calcium, Dietary / Q000378:metabolism*; D006224:Cricetinae; D004386:Duodenum / Q000378:metabolism*; D006706:Homeostasis; D007082:Ileum / Q000378:metabolism*; D007408:Intestinal Absorption; D007700:Kinetics; D008297:Male; D008647:Mesocricetus
D002136:Calcium, Dietary