Calbindin-D9k stimulates the calcium pump in rat enterocyte basolateral membranes.
Calbindin-D9k, a vitamin D-dependent Ca2+-binding protein, is closely associated with the transcellular absorption of calcium by mammalian enterocytes. Studies were performed to determine whether physiological concentrations of calbindin-D9k altered Ca2+ transport by the ATP-dependent Ca2+ pump in rat duodenal basolateral membrane vesicles. In solutions where free Ca2+ was buffered by EGTA, only a small stimulation of Ca2+ uptake rates could be demonstrated, and it was likely that this was secondary to changes in free Ca2+ concentration. However, a threefold stimulation of uptake by 30 microM calbindin-D9k was found when EGTA-free solutions were used, and changes in free Ca2+ activity or 45Ca2+ specific activity were avoided. The affinity for Ca2+ was reduced in this system but appeared to be stimulated by either calbindin-D9k or EGTA. Other Ca2+-binding proteins that bind Ca2+ in the micromolar range were found to increase Ca2+ uptake in the absence of EGTA. These experiments suggest that one of the actions of calbindin-D9k is to stimulate the rate of extrusion of Ca2+ from the enterocyte by increasing Ca2+ transport by the Ca2+ pump.
Walters
J R
JR
Department of Medicine, State University of New York, Buffalo General Hospital 14203.
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001345:Autoradiography; D001692:Biological Transport / Q000187:drug effects; D064026:Calbindins; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D004386:Duodenum / Q000378:metabolism; D004533:Egtazic Acid / Q000494:pharmacology; D007408:Intestinal Absorption; D007413:Intestinal Mucosa / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D051381:Rats; D064030:S100 Calcium Binding Protein G / Q000378:metabolism / Q000494:pharmacology*
D064026:Calbindins; D015220:Calcium Channels; D002135:Calcium-Binding Proteins; D064030:S100 Calcium Binding Protein G; C576508:S100g protein, rat; D004533:Egtazic Acid; D000255:Adenosine Triphosphate; D002118:Calcium