Sodium-extruding and calcium-extruding sodium/calcium exchangers display similar calcium affinities.
Na+/Ca2+ exchange activities in purely inside-out and mixed inside-out and right-side-out fish enterocyte basolateral plasma membrane vesicle preparations display equal affinities for Ca2+, showing that only the intracellular Ca2+ transport site of the Na+/Ca2+ exchanger is detected in experiments on vesicle preparations with mixed orientation. Therefore, Ca2+ pump and Na+/Ca2+ exchange activity may be compared directly without correction for vesicle orientation. The Na+/Ca2+ exchange activity in fish enterocyte vesicles is compared to the activity found in dog erythrocyte vesicles. The calcium-extruding exchanger in fish basolateral plasma membranes shows values of Km and V(max) for calcium similar to those found for the sodium-extruding exchanger in dog erythrocyte membranes, indicating that differences in electrochemical gradients underlie the difference in cellular function of the two exchangers.
Schoenmakers
T J
TJ
Department of Animal Physiology, Faculty of Science, University of Nijmegen, The Netherlands.
Flik
G
G
D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000097:blood / Q000378:metabolism* / Q000494:pharmacology; D002352:Carrier Proteins / Q000097:blood / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D004285:Dogs; D004910:Erythrocyte Membrane / Q000378:metabolism*; D005399:Fishes; D007413:Intestinal Mucosa / Q000378:metabolism*; D007700:Kinetics; D012964:Sodium / Q000097:blood / Q000378:metabolism*; D019831:Sodium-Calcium Exchanger
D002352:Carrier Proteins; D019831:Sodium-Calcium Exchanger; D012964:Sodium; D002118:Calcium