ALTERATIONS OF CA++ UPTAKE AND LIPID-CONTENT IN CULTURED HUMAN ARTERIAL SMOOTH-MUSCLE CELLS TREATED WITH 26-HYDROXYCHOLESTEROL

The effects of 26-hydroxycholesterol on Ca-45(++) uptake, [C-14]cholesterol uptake, [C-14] acetate incorporation and the concentrations of 26-hydroxycholestero1 and cholesterol in the plasma membrane were studied in cultured human smooth muscle cells isolated from umbilical arteries. The results showed that: (1) 26-hydroxycholesterol enhanced markedly Ca-45(++) uptake and the enhancement was not diminished by nifedipine; (2) 26-hydroxycholesterol decreased cholesterol content in plasma membrane by inhibiting cholesterol uptake and synthesis, and [C-14]cholesterol uptake was not LDL-receptor dependent; (3) 26-hydroxycholesterol induced a shift of [C-14] acetate from cholesterol into phospholipid synthesis, but the radioactive incorporation into triglyceride and cholesterol ester was inhibited by 26-hydroxycholesterol; and (4) 26-hydroxycholesterol inserted itself into the plasma membrane. We suggested that 26-hydroxycholesterol changes the composition of membrane lipids with a consequential alteration of membrane permeability to Ca++.