Analysis of the regulation of phosphatidylinositol-4,5-bisphosphate synthesis by arachidonic acid in exocrine pancreas

In pancreatic acinar cells prelabeled with either ³²P_i or myo-[³H]inositol, arachidonic acid (10-50 μm) rapidly decreased the steady-state levels of [³²P]phosphatidylinositol 4′,5′-bisphosphate ([³²P]PtdIns4,5P₂) and inhibited carbachol-stimulated accumulation of [³H]inositol trisphosphate ([³H]InsP₃). Both actions of arachidonic acid were rapidly reversed by bovine serum albumin (BSA). Indomethacin and nordihydoguaiaretic acid failed to block the inhibitory effects of arachidonic acid on [³²P]PtdIns4,5P₂ levels. Arachidonic acid (10-50 μm) also caused a prompt depletion of cellular ATP which was rapidly reversed by BSA. The ATP-depleting action of arachidonate paralleled in terms of concentration dependence and time course its inhibitory effects on [³²P]PtdIns4,5P₂ and [³H]InsP₃ levels. Exposure of acinar cells to 50 μm arachidonic acid produced an increase in oxygen consumption which exceeded that elicited by either carbachol or ionomycin. Arachidonic acid (10-50 μm) also caused a concentration-dependent rise in cytosolic Ca²⁺, which was partially obtunded by Ca²⁺ deprivation. A proposed mechanism involving arachidonic acid as a negative feedback regulator of polyphosphoinositide turnover in exocrine pancreas is discussed.