Arachidonic acid modulates [C-14]stearic acid incorporation into phosphatidylinositol, in human neuroblastoma cells

In the human neuroblastoma cell line SK-N-BE(2), arachidonic acid (AA), supplied in the medium at micromolar concentrations, markedly ehnanced [C-14]stearic acid (SA) (but not [C-14]palmitic acid or [C-14]oleic acid) incorporation into phosphatidylinositol (PtdIns). AA failed to stimulate [C-14]SA incorporation into PtdIns precursors, namely phosphatidic acid and cytidinediphosphodiacylglycerol; furthermore, enhanced [C-14]SA incorporation, brought about by exogenously administered AA, was not restricted to PtdIns tetraenoic species. When cells were pulsed for 1 h with [C-14]SA (either in the presence or absence of AA) and then reincubated in AA- and [C-14]SA-free medium, a marked loss of radioactivity from PtdIns was observed, that however was restricted to molecular species other than tetraenoic. These results are discussed in the light of possible mechanisms through which PtdIns achieves the 1-stearoyl-2-arachidonoyl configuration.