Modulation of neuronal phospholipase D activity under depolarizing conditions

Neuronal phospholipase D (PLD) activity was hypothesized to be involved in vesicle trafficking and endocytosis and, possibly, transmitter release. We here report that prolonged depolarization of rat hippocampal slices by pota ssium chloride (KCl) or 4-aminopyridine inhibited PLD activity. Similarly, PLD activity in rat cortical synaptosomes was significantly inhibited by de polarizing agents including veratridine and ouabain, Inhibition of calcium/ calmodulin kinase II (CaMKII) which positively modulates synaptosomal PLD a ctivity [Sarri et al, (1998) FEES Lett, 440, 287-290] by KN-62 caused a fur ther reduction of PLD activity in depolarized synaptosomes, Depolarization- induced inhibition of PLD activity was apparently not due to transmitter re lease or activation of other kinases, We observed, however, that KCl-induce d depolarization caused an increase of inositol phosphates and a reduction of the synaptosomal pool of phosphatidylinositol-4,5-bisphosphate (PIP2), M oreover, in synaptosomes permeabilized with Staphylococcus aureus alpha-tox in, PLD activation induced by calcium was abolished by neomycin, a PIP2 che lator, We conclude that depolarizing conditions cause an inhibition of neur onal PLD activity which is likely due to breakdown of PTP2, a required cofa ctor for PLD activity. Our findings suggest that neuronal PLD activity is r egulated by synaptic activity. (C) 1999 Federation of European Biochemical Societies.