DIFFERENTIAL PHOSPHOLIPID-METABOLISM IN RAT AORTIC SMOOTH-MUSCLE CELLS OF VARYING PROLIFERATIVE POTENTIAL UPON LONG-TERM EXPOSURE TO PHORBOL 12-MYRISTATE 13-ACETATE

Subchronic exposure of rats to allylamine (AAM) modulates aortic smoot h muscle cells (SMCs) from a quiescent to a proliferative phenotype. T his response is associated with alterations in phospholipid metabolism and protein kinase C (PKC) activity. The present studies were conduct ed to evaluate the effects of long-term exposure to phorbol 12-myrista te 13-acetate (PMA) on phospholipid metabolism in SMCs derived from co ntrol and AAM-treated animals, cells of varying proliferative potentia l. Measurements of P-32/[H-3]myristic acid incorporation into parent p hospholipids and phosphatidic acid (PA) and the extent of PKC-mediated histone phosphorylation were conducted following exposure of pre- and postconfluent subcultures of SMCs to PMA for 3 h. Increased P-32 inco rporation into phosphatidylcholine (PC) was observed in both pre- and postconfluent cultures of control and AAM cells treated with PMA relat ive to vehicle. This response was attenuated in pre- and postconfluent AAM cells relative to control counterparts. PMA enhanced P-32 incorpo ration into phosphatidylinositol (PI) in preconfluent cultures of cont rol cells, but decreased P-32 incorporation in cultures of AAM cells r elative to vehicle. A similar relationship was observed in the PI prof ile of postconfluent cultures. The alterations in primary phospholipid profiles induced by PMA correlated with the loss of PKC-mediated hist one phosphorylation in the cytosolic and particulate fractions of both cell types. The pattern of P-32 incorporation into PA, a phospholipid metabolite, paralleled that of PC in cultures of both cell types. In the presence of ethanol, vehicle-treated control and AAM cells exhibit ed a modest increase in phosphatidylethanol (PEt) formation, as measur ed by [H-3]myristic acid incorporation. PMA enhanced PEt formation in control and AAM cultures, but selectively decreased [H-3]myristic acid incorporation into PA in AAM cells. These data demonstrate that long- term PMA treatment differentially modulates phospholipid metabolism in aortic SMCs of varying proliferative potential. These alterations are associated with modulation of PLD-mediated hydrolysis of membrane pho spholipids.