AbstractThe addition of human platelet‐derived growth factor (PDGF) to confluent, quiescent cultures of human diploid fibroblasts induced the rapid breakdown of cellular polyphosphoinositides. The levels of32P‐labeled phosphatidylinositol 4,5‐bisphosphate (PIP2), phosphatidylinositol 4‐phosphate (PIP), and phosphatidylinositol (PI) decreased by 30 to 40 within 1 min after exposure of the cells to PDGF. The levels of PIP and PIP2returned to their initial values within 3 and 10 min, respectively, after PDGF addition. The level of PI continued to increase after it had returned to control values and was up threefold within 30 min after PDGF addition. In cells prelabeled withmyo‐3Hinositol PDGF caused an eightfold increase in the levels of inositol trisphosphate (IP3) within 2 min. Lesser increases, twofold and 1.3‐fold, respectively, were seen in levels of inositol bisphosphate (IP2) and inositol monophosphate (IP). Within 10 min after PDGF addition the levels of all three inositol phosphates had decreased to control values. The levels of IP3measured 2 min after PDGF addition depended on the PDGF concentration and were maximal at 5–10 ng/ml of PDGF. Similar concentrations of PDGF stimulate maximal cell growth and DNA synthesis i
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