We examined an early action of erythroid differentiation factor (EDF), a polypeptide which induces differentiation of Friend murine erythroleukemia (MEL) cells. (Eto et al., Biochem. Biophys. Res. Commun. 142: 1095–1103, 1987). In MEL cells, EDF caused a rapid and transient increase in cytoplasmic concentration of free calcium, [Ca 2+] c. EDF increased [Ca 2+] c even in the absence of extracellular calcium. When [ 3H]inositol-labeled MEL cells were incubated with EDF, EDF rapidly increased radioactivity in inositol trisphosphate, bisphosphate and monophosphate. EDF also increased [ 3H] diacylglycerol in [ 3H]arachidonate-labeled MEL cells. These results indicate that EDF increases [Ca 2+] c by stimulating hydrolysis of polyphosphoinositide.
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