MEMBRANE-ASSOCIATED PHOSPHOLIPASE-D ACTIVITY IN NEURAL CELL-LINE PC12

Stimulation of PC12 cells with carbachol (Cch) or phorbol 12-myrisrate 13-acetate (PMA) induced [H-3]phosphatidylbutanol (PBut) production. Depletion of extracellular Ca2+ abolished the Cch-mediated phospholipa se D (PLD) activation, indicating the requirement of Ca2+ influx. Two different types of PLD activity, oleate-dependent and GTP gamma S-depe ndent, were examined by using exogenous [H-3]phosphatidylcholine subst rate. PLD activity of the membrane fraction of PC12 cells was highly d ependent on oleate and independent of GTP gamma S. This profile is in sharp contrast to that observed in HL60 cells showing the profound GTP gamma S-induced activation of PLD. The oleate-dependent PLD activity of PC12 membrane was inhibited by high concentrations of Ca2+ and Mg2. These results indicate that Ca2+ may not directly activate PLD but t hrough some Ca2+-dependent mechanism(s) in Cch-stimulated cells.