Labeling Of Phosphatidate Research Articles

Phosphatidic acid metabolism, calcium ions and transmitter release from electrically stimulated synaptosomes

Synaptosomes isolated from guinea pig brain cortex were stimulated electrically in a medium containing [32P]-orthophosphate. The electrical stimulation caused increased labelling of phosphatidic acid in a synaptic vesicle fraction prepared by osmotic shock of the incubated synaptosomes. Electrical stimulation also provokes transmitter release from the synaptosomes. Both increased phosphatidate labelling and transmitter release required calcium ions in the medium. The effects are discussed in relation to earlier work with acetylcholine and the possible involvement of membrane phosphatidic acid in transmitter release by exocytosis.

Effects of Acetylcholine on Labeling of Phosphatidate and Phosphoinositides by [32P]Orthophosphate in Nerve Ending Fractions of Guinea Pig Cortex

Abstract The effect of acetylcholine on the incorporation of 32Pi into phospholipids was studied in subfractions of guinea pig cerebral cortex obtained by sucrose density fractionation. Incorporation of label into phosphatidic acid and phosphatidylinositol was stimulated approximately 100 and 70%, respectively, by 10-4 m acetylcholine in a nerve ending fraction rich in acetylcholine esterase. The effect was not significant in other subcellular fractions investigated, including a denser nerve ending fraction. This action of acetylcholine was blocked by the addition of atropine but not by tubocurare. Labeling of phosphatidylinositol phosphate and phosphatidylinositol diphosphate was inhibited by about 20% in the presence of 10-4 m acetylcholine. This inhibition was not specific for any of the subfractions and was not affected by the addition of atropine.

Tetraphenylborate stimulation of phospholipid labeling in goldfish brain

The presence of tetraphenylborate (TPB, 10 −3 M to 10 −4 M) in goldfish brain particulate preparations during a 5–15 min incubation with γ- 32P-ATP or γ- 33P-ATP results in marked stimulation of labeling of phosphatidate and a decrease in labeling of phosphatidyl inositol phosphate. Incorporation into phosphatidyl inositol diphosphate, a minor labeled phospholipid, is also depressed by TPB. We suggest the TPB effect is mediated by stimulation of a phosphodiesterase releasing diglyceride from phospholipid, which then reacts with labeled ATP, catalyzed by diglyceride kinase.