Calf serum induced the phospholipase C-mediated hydrolysis of phosphoinositides in normal rat kidney (NRK) cells transformed by a temperature-sensitive Kirsten murine sarcoma virus (tsK-NRK cells). Various growth factors known to induce the phospholipase C reactions in other cell types, such as platelet-derived growth factor, fibroblast growth factor, epidermal growth factor, thrombin, vasopressin, bombesin, cholecystokinin, and prostaglandin F, did not induce phospholipase C reactions in the transformed NRK cells. Furthermore, noradrenaline, histamine, dopamine, angiotensin II, carbachol, and tumor growth factor-β did not induce phospholipase C reactions. However, serotonin did induce phospholipase C reactions. The amount of serotonin contained in the calf serum was sufficient to support 50% of the activity promoted by the serum itself, and calf serum-induced phospholipase C reactions were inhibited to 10–20% of the original level by ketanserin and methysergide, known to be antagonists for the serotonin receptors. Dialysis almost completely removed serotonin from calf serum and reduced the serum-induced phospholipase C reactions. Moreover, the phospholipase C reactions induced by calf serum and serotonin were inhibited by pretreatment of the cells with pertussis toxin or 12-O-tetradecanoylphorbol-13-acetate. These results indicate that serotonin is one of the major serum factors inducing phospholipase C-mediated hydrolysis of phosphoinositides in transformed NRK cells. Serotonin induced phospholipase C reactions not only in tsK-NRK cells but also in nontransformed NRK cells. However, serotonin did not induce these reactions in Swiss 3T3 cells or NIH 3T3 cells.

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This investigation was supported by Grants-in-Aid for Scientific Research and Cancer Research from the Ministry of Education, Science, and Culture, Japan (1987, 1988); by Grants-in-Aid for Abnormalities in Hormone Receptor Mechanisms (1987, 1988), Cardiovascular Diseases (1987, 1988), and Cancer Research (1988) from the Ministry of Health and Welfare, Japan; and by grants from the Yamanouchi Foundation for Research on Metabolic Disease (1987) and the Research Program on Cell Calcium Signal in the Cardiovascular System (1987, 1988).

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