Rapid breakdown of phosphatidylinositol accompanied by accumulation of phosphatidic acid and diacylglycerol in rat lymphocytes stimulated by concanavalin A.

Concanavalin A stimulated the [32P]phosphate incorporation into phospholipids of rat lymph-node cells in a dose-dependent manner up to 200 microgram of the lectin per ml of the lymphocyte culture. The initial step in the concanavalin A-stimulated phospholipid metabolism was examined by use of rat lymphocytes prelabeled with radioactive arachidonic acid. Concanavalin A induced a small but significant decrease, up to 10%, in the phosphatidylinositol radiolabel at 1 to 5 min after the lectin addition. A small increase, about 10%, in the diacylglycerol radiolabel and a twofold increase in the phosphatidate radiolabel were observed concomitant with the breakdown of phosphatidylinositol. The increase in the phosphatidic acid radioactivity amounted to about one-fifth of the decrease in the phosphatidylinositol radioactivity. No significant change in radiolabel was found in the other major phospholipids or in triacylglycerol. The results suggest that the breakdown of pre-existing phosphatidylinositol is the initial step in the lymphocyte phosphatidylinositol response.