PHOSPHATIDIC-ACID PROMOTES PHOSPHOINOSITIDE METABOLISM AND DNA-SYNTHESIS IN CULTURED CORTICAL ASTROCYTES

The addition of exogenous phosphatidic acid (PA) to cultured cortical astrocytes prelabelled with [H-3]inositol resulted in the accumulation of intracellular [H-3]inositol phosphates (IP) in a concentration-dep endent (EC(50) = 20 mu M) manner. Analysis of the individual IPs forme d following a PA challenge revealed a rapid but transient generation o f [H-3]inositol trisphosphate (IP3) indicating the involvement of phos phatidylinositol 4,5-bisphosphate (PIP2) breakdown in this response a fact which was confirmed when the recovery of radiolabel in membrane p hosphoinositides was assessed. PA's ability to stimulate IP3 accumulat ion was found to be dependent upon its acyl-chain length. Dioleoyl-PA (C-18:1) was equally as effective as PA from egg yolk lecithin in this respect whilst dipalmitoyl-PA (C-16:0) was less so and dimyristoyl-PA (C-14:0) and dilauroyl-PA (C-12:0) were without effect. In subconflue nt, serum-deprived cultures, PA was found to increase DNA synthesis fo llowing a 48 h exposure period. This effect was observed over the same concentration range used to measure phosphoinositide breakdown and wa s found to be mediated by the activation of protein kinase C. As with its effect on phosphoinositide metabolism, PA's ability to promote DNA synthesis was correlated with its acyl-chain length. These data show that PA is capable of stimulating both phosphoinositide metabolism and DNA synthesis in cultured astrocytes possibly via the activation of s pecific membrane receptors. However, the precise relationship between these events remains to be elucidated.