Association of phospholipid‐cholesterol micelles with rat heart mitochondria: Stimulators and inhibitors

The uptake of emulsified labeled lipids by rat heart mitochondria was studied. Divalent cations greatly stimulated uptake of cholesterol in emulsions containing phospholipids; the effect increased with increasing atomic number. Epinephrine and norepinephrine were also stimulatory. Lipid‐depleted mitochondria were less effective in taking up cholesterol unless lecithin or serum lipids were included in the emulsion. Addition of iodoacetamide did not inhibit uptake, while use of heated mitochondria or extremes of pH augmented lipid uptake. Thus the process appears to be non‐enzymatic. While lecithin emulsions showed no visible change on addition of calcium ions, phosphatidylethanolamine emulsions became turbid and the turbidity was largely removed by addition of heparin. Heparin as well as chondroitin sulfate B and nonionic detergent did inhibit lipid uptake by mitochondria. The possible role of such nonenzymatic lipid uptake in membrane formation and cholesterol accumulation is discussed.