Characterization of ATP-dependent Ca2+ uptake by canine brain microsomes with saponin.
ATP-dependent Ca2+ uptake by brain microsomes was classified into two fractions according to the sensitivity to saponin. Properties of each fraction of Ca2+ uptake were examined and compared with those of inside-out membrane vesicles of erythrocyte and cardiac sarcoplasmic reticulum. The concentration of saponin for 50% inhibition (IC50) of major saponin-sensitive Ca2+ uptake was 11 micrograms/ml, and this uptake was enhanced by calmodulin. The minor saponin-insensitive Ca2+ uptake fraction (IC50; 90 micrograms/ml) was not affected by calmodulin but was enhanced by oxalate or 0.1 M KCl. The IC 50 of saponin for inside-out membrane vesicles of erythrocyte and cardiac sarcoplasmic reticulum was 11.3 and 114.8 micrograms/ml, respectively. A characteristic ring-like saponin-cholesterol micellar structure was observed electron microscopically in most membrane vesicles of brain microsomes and erythrocyte membrane vesicles but not in the cardiac sarcoplasmic reticulum. These observations indicate that saponin-sensitive and insensitive Ca2+ uptake was derived from plasma membranes and endoplasmic reticulum, respectively. Saponin proved useful for distinguishing the Ca2+ transport activity of plasma membrane from the Ca2+ uptake of other cellular organelles in the membrane preparations.
D000255:Adenosine Triphosphate / Q000502:physiology*; D000818:Animals; D001921:Brain / Q000378:metabolism* / Q000648:ultrastructure; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D004285:Dogs; D004912:Erythrocytes / Q000378:metabolism; D008854:Microscopy, Electron; D008861:Microsomes / Q000378:metabolism* / Q000648:ultrastructure; D009206:Myocardium / Q000378:metabolism; D012503:Saponins; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D012964:Sodium / Q000378:metabolism
D012503:Saponins; D000255:Adenosine Triphosphate; D012964:Sodium; D002118:Calcium