The breakdown of phosphatidylinositol in myoblasts stimulated to fuse by the addition of Ca2+.
1. The fusion of chick-embryo myoblasts to produce myotubes was studied. The myoblasts were grown for 50 h in medium containing 10--20 microM-Ca2+; during this period they achieve fusion competence. 2. A rapid breakdown of phosphatidylinositol is also observed on addition of 1.4 mM-Ca2+ to these cells. This Ca2+ concentration also stimulates rapid myoblast fusion. 3. The breakdown is complete within 15 min and shows the same dependence on Ca2+ concentration as the fusion process. 4. Fusion-incompetence myoblasts and cells where fusion is inhibited by sodium butyrate exhibit no phosphatidylinositol breakdown on Ca2+ addition. 5. The Ca2+ ionophore A23187 inhibits the Ca2+-stimulated breakdown by about 50%, but has no effect on fusion. 6. A concomitant increase in 1,2-diacylglycerol labelled and fall in phosphatidylinositol labelling was observed when the lipids were labelling with [14C]glycerol on increasing the Ca2+ concentration in the medium to 1.4 mM. 7. We propose that the breakdown of phosphatidylinositol with a resultant increase in 1,2-diacylglycerol content of the cell membrane promotes myoblast fusion.
D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002459:Cell Fusion / Q000187:drug effects; D002478:Cells, Cultured; D002642:Chick Embryo; D004075:Diglycerides / Q000378:metabolism; D009132:Muscles / Q000187:drug effects / Q000196:embryology / Q000378:metabolism*; D010716:Phosphatidylinositols / Q000378:metabolism*; D010743:Phospholipids / Q000378:metabolism; D013268:Stimulation, Chemical
C011439:1,2-diacylglycerol; D004075:Diglycerides; D010716:Phosphatidylinositols; D010743:Phospholipids; D002118:Calcium