Active Ca2+ transport in plasma membranes of branchial epithelium of the North-American eel, Anguilla rostrata LeSueur.
A branchial epithelial membrane fraction, more than 20-fold enriched in Na+/K+-ATPase activity when compared with the crude homogenate of the tissue, was obtained from adult freshwater American eels. In a membrane vesicle preparation that consisted of 33% inside-out, 23% right-side-out and 44% leaky vesicles, the accumulation of 45Ca2+ was stimulated by ATP, but not by ADP. Accumulation of 45Ca2+ was prevented when vesicles were pretreated with detergent or the Ca2+ ionophore A23187; Ca2+ efflux was observed when the ionophore was added to actively 45Ca2+-loading vesicles. Oxalate did not affect Ca2+ accumulation in these vesicles. Kinetic analysis of the Ca2+-transport process by an Eadie-Hofstee plot revealed that the process is homogeneous; its kinetic parameters are a K0.5 for Ca2+ of 0.053 microM and a Vmax of 2.25 nmol Ca2+/min.mg protein (at 37 degrees C). The calmodulin dependency of this Ca2+ transporting process was shown by the inhibitory action of calmodulin antagonists and by the stimulatory effect of calmodulin repletion after EGTA treatment of the membranes. We conclude that an ATP-energized Ca2+ pump is present in the plasma membranes of branchial epithelium, that resembles the Ca2+ pumps of e.g. mammalian intestinal or renal plasma membranes, and propose its involvement in branchial Ca2+-uptake from the water.
G
G
Flik
S E
SE
Wendelaar Bonga
J C
JC
Fenwick
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000811:Anguilla / Q000378:metabolism*; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D004848:Epithelium / Q000378:metabolism; D005260:Female; D005880:Gills / Q000187:drug effects / Q000378:metabolism*; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism; D007700:Kinetics; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism
D007473:Ion Channels; D000001:Calcimycin; D000255:Adenosine Triphosphate; D000254:Sodium-Potassium-Exchanging ATPase; D002118:Calcium