The binding of tritium-labeled cardiac glycosides by sarcoplasmic reticulum and by cell membrane isolated from cat heart

The binding capacity of ouabain or digitoxin by sarcoplasmic reticulum (SRF) isolated from cat heart muscle was found to be about 7-9 times as much as that by cell membrane from cat heart muscle. Acetone treatment of SRF caused a marked decrease in the binding capacity of ouabain and digitoxin. SRF pretreated with phospholipase C was decreased in content of phospholipid, in the ATPase activity, in the Ca-binding capacity and in the binding capacity of ouabain or digitoxin, while SRF pretreated with digitonin was decreased in content of cholesterol, but not in phospholipid content, in ATPase activity, in the Ca-binding capacity and in the binding capacity of ouabain or digitoxin. From these findings, it might be concluded that SRF was the major binding site for cardiac glycosides and that the content of phospholipid of SRF plays an important role in the drug-binding capacity.