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

The effects of 26-hydroxycholesterol on Ca-45(++) uptake, [C-14]choles terol uptake, [C-14] acetate incorporation and the concentrations of 2 6-hydroxycholestero1 and cholesterol in the plasma membrane were studi ed in cultured human smooth muscle cells isolated from umbilical arter ies. The results showed that: (1) 26-hydroxycholesterol enhanced marke dly Ca-45(++) uptake and the enhancement was not diminished by nifedip ine; (2) 26-hydroxycholesterol decreased cholesterol content in plasma membrane by inhibiting cholesterol uptake and synthesis, and [C-14]ch olesterol uptake was not LDL-receptor dependent; (3) 26-hydroxycholest erol induced a shift of [C-14] acetate from cholesterol into phospholi pid 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 sugges ted that 26-hydroxycholesterol changes the composition of membrane lip ids with a consequential alteration of membrane permeability to Ca++.