MATERIALS AND METHODS Male Sprague-Dawley rats weighing approximately 200-250 g were kept in environmentally controlled quarters for 1-2 weeks prior to experimental use. Adrenal zona glomerulosa cells were prepared by methods described by Fakunding et al.(8). These cells were resuspended in Medium 199 containing 5 mM K+ and 2 mg of bovine serum albumin/ml, distributed to plastic incubation vials (approximately 200,000-500,000 cells in 0.5 ml of medium), and incubated at 37" C under 95% 0 2 and 5% C02 with SO pCi of (3'P) H3P0, for 120 min unless indicated otherwise. After incubation, media were separated from cells by centrifugation and stored at-70" C for subsequent aldosterone analysis. As described previously (1-4), cellular phospholipids were extracted, and phospholipids were purified by thin layer chromatography employing solvent system B. The latter solvent system provides a clean separation of phosphatidylinositol, phosphatidylserine, phosphatidic acid, and diphosphoinositide. Triphosphoinositide tends to stay close to the origin unless longer running times are employed and was therefore not routinely evaluated in most of the present experiments. Phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, and sphingomyelin run together just behind cardiolipin, which in turn migrates just behind neutral lipids which are near the solvent front. Radioactive phospholipids were identified by radioautography and acid charring and counted for radioactivity in a liquid scintillation counter as described previously