THE LABELLING OF NERVE ENDING PHOSPHOLIPIDS IN GUINEA‐PIG BRAIN IN VIVO AND THE EFFECT OF ELECTRICAL STIMULATION ON PHOSPHATIDYLINOSITOL METABOLISM IN PRELABELLED SYNAPTOSOMES

Abstract

Abstract— The intracerebral injection of 32Pi into guinea‐pig cortex resulted in a steady rate of incorporation into all phospholipids over a 20 h period. The specific radioactivities of phosphatidate and phos‐phatidylinositol in synaptosomes prepared from cortex prelabelled, in vivo, were at a maximum after 2 h and the respective activities were 3–8 times higher than in whole cortex. This peak in labelling corresponded with the maximum specific activity of the brain ATP. No similar differential labelling pattern was observed for phosphatidylethanolamine, phosphatidylcholine and phosphatidylserine. Electrical stimulation of the prelabelled synaptosomes produced a rapid drop in the specific activity of phosphatidylinositol and phosphatidate and an increase in the specific activity of CDP‐diacylglycerol. The specific activity of synaptosomal ATP was not affected. Study of the subsynaptosomal fractions obtained after osmotic rupture of the synaptosomes revealed that the most highly labelled phosphatidylinositol was in the synaptic vesicle fraction (D) and the most active phosphatidate was in a ‘microsomal’ fraction (E). Electrical stimulation caused a loss of phosphatidylinositol radioactivity from fraction D and a loss of phosphatidate radioactivity from fraction E. The specific activity of these lipids in other fractions was not affected. A possible role for presynaptic phosphatidylinositol is suggested.

Polyphosphoinositol lipids: Under‐PPInning synaptic function in health and disease

“…This effect was accelerated by stimulation with acetylcholine (ACh), and was accompanied by rapid incorporation of 32 P into phosphatidic acid (PtdOH) (Hokin and Hokin, 1955). A similar effect was subsequently observed after electrical stimulation of isolated nerve terminals (Pickard and Hawthorne, 1978). We now know that this occurs due to the activation of PLC, leading to the conversion of DAG into PtdOH by DAG-kinase [ Fig.…”

Phosphorylation of B‐50 (GAP43) Is Correlated with Neurotransmitter Release in Rat Hippocampal Slices

“…This would imply a depolarizationdependent generation of diacylglycerol (DAG), a mechanism that has emerged from various experimental designs. Breakdown of phosphatidylinositol (implicating generation of DAG) has been observed in synaptosomes after electrical (Pickard and Hawthorne, 1978) and high-K+ stimulation (Wei and Wang, 1987). This breakdown most likely occurs through the activation of phospholipase C by incoming Ca2' because the effect on phosphatidylinositol breakdown can be mimicked by the calcium ionophore A23 187 (Griffin and Hawthorne, 1978;Wei and Wang, 1987).…”

The Nutritional Significance, Metabolism, and Function of myo-Inositol and Phosphatidylinositol in Health and Disease

“…The cholinergic phosphatidylinositol effect has been postulated as an essential part of the synaptic transmission process (Durrell et at., 1969). Pickard and Hawthorne (1978b) have provided details on the possible role of phosphatidylinositol turnover in transmitter release by showing that electrical stimulation of synapto-somes labeled with 32p in vivo caused a loss of radioactivity from the phosphatidylinositol associated with the synaptic vesicles.…”