FIG. 1.

Changes in PI-3,4-P₂ and PI-3,4,5-P₃ levels during 3T3-L6 myoblast differentiation. Cells were seeded at a low density (10% confluence) and maintained in medium supplemented with 10% FCS. Twenty-four hours prior to harvesting the lipids or proteins, the medium was changed to DMEM containing 10% FCS (dashed lines) or 1% FCS (solid black lines), supplemented with [³H]inositol (B, I, and J). (A) The expression of the myogenic markers m-cadherin and MHC during the course of 3T3-L6 differentiation was determined by Western blot analysis. (B) The levels of PI-3,4-P₂ (squares) and PI-3,4,5-P₃ (triangles) in differentiating 3T3-L6 myoblasts were measured by HPLC analysis after metabolic labeling of the cells for 24 h. Also shown are the levels of PI-3-P in cells labeled in medium containing 10% FCS or 1% FCS. (C to H) Phase-contrast microscopy photos of the 3T3-L6 cultures in medium containing 1% FCS (C to E) or 10% FCS (F to H), before cells were collected at day 2 (C and F), day 4 (D and G), or day 5 (E and H). (I and J) HPLC profile of the deacylated phosphoinositides in 3T3-L6 cells labeled for 24 h with [³H]inositol in medium containing 10% FCS (I) or 1% FCS (J) on day 4 of differentiation. The data shown are representative of more than three independent measurements.