Effect of Ca++ on triphosphoinositide extraction in fusing myoblasts

Ca++-dependent degradation of triphosphoinositide has been postulated to regulate levels of membrane-bound Ca++ and to generate a 1,2-diacylglycerol fusogen in cell fusion. Triphosphoinositide metabolism was therefore studied during Ca++-induced fusion of cultured chick embryo myoblasts. Using a frequently cited extraction procedure, it was found that apparent Ca++-dependent triphosphoinositide degradation was actually due to inhibition of extraction. A new procedure using the ion-pairing reagent tetrabutylammonium sulfate was developed which was unaffected by Ca++ and gave 2- to 20-fold greater extraction of triphosphoinositide than existing procedures. With this procedure, no changes in triphosphoinositide metabolism were found during myoblast fusion.