Intestinal calcium transport and calcium extrusion processes at the basolateral membrane.
The intestinal absorption of calcium has been proposed to occur by the transcellular transfer of Ca2+ through the enterocyte proper and between the cells of the intestinal epithelium, i.e., the paracellular path. Attention in this report is given to the transcellular models of Ca2+ absorption and, more specifically, the Ca2+ extrusion events occurring at the basolateral membrane. These extrusion processes include the operation of an ATP-dependent Ca2+ pump and a Na+/Ca2+ exchanger, as well as exocytosis as the terminal event in a proposed vesicular transport mechanism. Evidence for the presence of an ATP-dependent Ca2+ pump at the basolateral membrane is documented and illustrated with biochemical and immunological data from studies on the avian intestinal basolateral membrane. As shown immunohistochemically, the Ca2+ pump was primarily localized on the enterocyte basolateral membrane. The ATP-dependency and vitamin D enhancement of Ca2+ uptake by isolated basolateral membrane vesicles are shown. Western blot analysis of intestinal mucosa, by using a monoclonal antibody produced against the erythrocyte Ca2+ pump, indicated that the number of pump units is increased by 1,25-dihydroxycholecalciferol. The possible involvement of calbindin-D28K as a direct stimulator of the Ca2+ pump is discussed, and the quantitative relationship between Ca2+ transport rates and Ca2+ pumping activity has been estimated. Information related to the basolateral membrane Na+/Ca2+ exchanger and the vesicular transport model of Ca2+ absorption is also briefly reviewed.
Wasserman
R H
RH
Department of Physiology, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853.
Chandler
J S
JS
Meyer
S A
SA
Smith
C A
CA
Brindak
M E
ME
Fullmer
C S
CS
Penniston
J T
JT
Kumar
R
R
D000818:Animals; D001693:Biological Transport, Active; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000502:physiology; D002462:Cell Membrane / Q000378:metabolism; D006801:Humans; D007408:Intestinal Absorption; D007413:Intestinal Mucosa / Q000378:metabolism*; D007422:Intestines / Q000648:ultrastructure
D000252:Calcium-Transporting ATPases; D002118:Calcium