Phorbol esters stimulate phosphoinositide phosphorylation and phosphatidylcholine metabolism in brain microvessels

The effects of 12-O-tetradecanoyl-phorbol-13-acetate (TPA) on phosphoinositide metabolism in cerebral microvessels were examined. Treatment of microvessels with TPA evoked a dose-dependent increase in the 32P-orthophosphate incorporation into polyphosphoinositides, phosphatidic acid (PA) and phosphatidylcholine (PC). The effect on PC was found only after a lag period. Experiments with membranes isolated from microvessels indicated a TPA-induced activation of phosphoinositide kinases. Evidence that this effect was mediated by protein kinase C (PKC) activation was provided by the reversal of the effect in the presence of staurosporine. Concomitantly with these observations, an increase of diacylglycerol (DAG) production was evoked without formation of inositol phosphates. Therefore, we suggest that TPA also stimulates PC metabolism. These results support a regulatory role for PKC in phospholipid signaling pathways in the blood-brain barrier (BBB).