Figure 4.

Radioactive PtdOH detected after 10 min of exposure at 0°C in cells supplemented with increasing concentrations of nonradioactive PO₄³⁻ prior to the temperature shift. Phospholipids were labeled in presence of 53 MBq L⁻¹ [³³P]-PO₄³⁻ for 105 min at 22°C. Cells were then supplemented with increasing concentrations of nonradioactive PO₄³⁻. After 15 min, cells were transferred to 0°C. Lipids were extracted after 10 min of exposure, and were separated by TLC using an acidic solvent system. PtdOH content was quantified as a fraction of total radiolabeled phospholipids. PtdOH produced in presence of nonradioactive PO₄³⁻ is expressed as a percentage of the level of PtdOH attained in cells with no added PO₄³⁻. Data are the mean of three independent experiments (±sd).