Stimulation of plasma membrane Ca2+ pump by calbindin-D28k and calmodulin is additive in EGTA-free solutions
Timmermans, J.A.; Bindels, R.J.; Van Os, C.H.
Journal of Nutrition 125(7 Suppl): 1981s-1986s
1995
ISSN/ISBN: 0022-3166 PMID: 7602380 Document Number: 453513
In enterocytes and erythrocytes a calmodulin-stimulated Ca-2+-ATPase is the main Ca-2+ efflux pathway. Previous studies have shown that in enterocytes this Ca-2+-pumping ATPase could be stimulated by vitamin D-dependent Ca-2+-binding protein, calbindin-D-9k, in ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA)-free solutions. In contrast, a similar stimulatory effect of calbindin-D-9K was not observed in erythrocytes. We reinvestigated the effects of calbindin, parvalbumin and calmodulin on active Ca-2+ uptake in membrane vesicles derived from porcine erythrocytes and from rat duodenum. In EGTA-containing solutions, neither calbindin-D-28k nor parvalbumin influenced the rate of ATP-dependent Ca-2+ uptake in red blood cell-derived vesicles. However, when EGTA-free solutions were used, calbindin D-28k and parvalbumin significantly increased ATP-dependent Ca-2+ uptake in erythrocyte as well as in enterocyte-derived membrane vesicles. In contrast, calmodulin significantly increased active Ca-2+ uptake in erythrocyte vesicles in the absence as well as in the presence of EGTA. In addition, ATP-dependent Ca-2+ uptake in the presence of 0.2 mu-M calmodulin was further increased by parvalbumin in the absence but not in the presence of EGTA. This observation precludes that parvalbumin and calbindin stimulate the plasma membrane Ca-2+ ATPase by occupying the calmodulin binding site. Our results support the theoretical notion that calbindin and parvalbumin stimulate the Ca-2+-starved pump by increasing the free Ca-2+ in the immediate vicinity of the Ca-2+ pump sites.