Phosphatidic Acid Accumulation and Catecholamine Release in Adrenal Chromaffin Cells: Stimulation by High Potassium and by Nicotine, and Effect of a Diacylglycerol Kinase Inhibitor R 59 022

Using primary cultures of bovine adrenal chromaffin cells labelled with ³²P_i, we show that stimulation with bradykinin, nicotine, or a depolarising concentration of potassium stimulates the accumulation of [³²P]phosphatidic acid. The effects of nicotine and potassium are smaller than the effect of bradykinin, and are dependent entirely on extracellular calcium. The diacylglycerol kinase inhibitor R 59 022 attenuates the formation of phosphatidic acid by nicotine and depolarising concentrations of potassium. This inhibitor also blocks the nicotine and potassium stimulation of nor‐ adrenaline release from Chromaffin cells. Using ⁴⁵Ca²⁺ influx studies, we show that the nicotine‐evoked calcium influx is also attenuated by R 59 022. These observations contrast with those in another report in which we showed that bradykinin stimulation of either [³²P]phosphatidic acid accumulation or noradrenaline release is not affected by R 59 022. It is likely that the calcium influx produced by nicotine and depolarising potassium is blocked by R 59 022 by a mechanism that is independent of its ability to block diacylglycerol kinase. The nicotine‐ and potassium‐stimulated [³²P]phosphatidic acid accumulation is a consequence of this calcium influx and presumably reflects calcium activation of either phospholipase C or phospholipase D.