title: Intestinal calcium transport and calcium extrusion processes at the basolateral membrane.
abstract: 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.
authors.affiliation: Department of Physiology, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853.
authors.forename: R H
authors.initials: RH
authors.lastname: Wasserman
authors.forename: J S
authors.initials: JS
authors.lastname: Chandler
authors.forename: S A
authors.initials: SA
authors.lastname: Meyer
authors.forename: C A
authors.initials: CA
authors.lastname: Smith
authors.forename: M E
authors.initials: ME
authors.lastname: Brindak
authors.forename: C S
authors.initials: CS
authors.lastname: Fullmer
authors.forename: J T
authors.initials: JT
authors.lastname: Penniston
authors.forename: R
authors.initials: R
authors.lastname: Kumar
mesh_terms: 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
chemical_list: D000252:Calcium-Transporting ATPases; D002118:Calcium