Effects of insulin and protein synthesis inhibitors on phospholipid metabolism, diacylglycerol levels, and pyruvate dehydrogenase activity in BC3H-1 cultured myocytes.
BC3H-1 myocytes were cultured with 32PO4 for 3 days to label phospholipids to constant specific activity. Subsequent treatment with physiological concentrations of insulin provoked 40-70% increases in 32PO4 levels (reflecting increases in mass) in phosphatidic acid, phosphatidylinositol, and polyphosphoinositides, and, lesser, 20-25% increases in phosphatidylserine and the combined chromatographic area containing phosphatidylethanolamine plus phosphatidylcholine plus phosphatidylcholine. Insulin-induced increases in phospholipids were significant within 5 min and near-maximal at 15-30 min. Comparable rapid insulin-induced increases in [3H]phosphatidylinositol were observed in myocytes prelabeled with [3H]inositol. These insulin effects (as per prolonged pulse-chase experiments) were due to increase phospholipid synthesis rather than decreased phospholipid degradation. Cycloheximide (and puromycin) pretreatment prevented insulin-induced increases in phospholipids and rapidly reversed ongoing insulin effects on phospholipids and pyruvate dehydrogenase activity. Insulin also rapidly increased diacylglycerol levels. These findings suggest that: (a) insulin provokes rapid increases in de novo synthesis of phosphatidic acid and its derivatives, e.g. phosphoinositides and diacylglycerol; (b) protein synthesis inhibitors diminish phospholipid levels in insulin-treated (but not control) tissues by increasing phospholipid degradation (?phospholipase(s) activation); and (c) changes in phospholipids and diacylglycerol may be important for changes in pyruvate dehydrogenase and other enzymatic activities during treatment with insulin and/or protein synthesis inhibitors.
D000818:Animals; D002460:Cell Line; D003513:Cycloheximide / Q000494:pharmacology; D004075:Diglycerides / Q000378:metabolism*; D005989:Glycerides / Q000378:metabolism*; D007328:Insulin / Q000494:pharmacology*; D009132:Muscles / Q000187:drug effects / Q000378:metabolism*; D010743:Phospholipids / Q000378:metabolism*; D011691:Puromycin / Q000494:pharmacology; D011768:Pyruvate Dehydrogenase Complex / Q000378:metabolism*; D013997:Time Factors
D004075:Diglycerides; D005989:Glycerides; D007328:Insulin; D010743:Phospholipids; D011768:Pyruvate Dehydrogenase Complex; D011691:Puromycin; D003513:Cycloheximide