1. Characterization of ATP-dependent Ca2+ uptake by canine brain microsomes with saponin
- Author
-
Iwao Ohtsuki and Tetsuaki Inamitsu
- Subjects
Erythrocytes ,Calmodulin ,chemistry.chemical_element ,Calcium ,complex mixtures ,Biochemistry ,Divalent ,Adenosine Triphosphate ,Dogs ,Microsomes ,parasitic diseases ,Animals ,chemistry.chemical_classification ,biology ,Chemistry ,Myocardium ,Endoplasmic reticulum ,Vesicle ,Cell Membrane ,Sodium ,Brain ,Saponins ,Membrane transport ,musculoskeletal system ,carbohydrates (lipids) ,Microscopy, Electron ,Sarcoplasmic Reticulum ,Membrane ,Microsome ,biology.protein - Abstract
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.
- Published
- 1984