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 potassium chloride (KCl) or 4-aminopyridine inhibited PLD activity. Similarly, PLD activity in rat cortical synaptosomes was significantly inhibited by depolarizing agents including veratridine and ouabain. Inhibition of calcium/calmodulin kinase II (CaMKII) which positively modulates synaptosomal PLD activity [Sarri et al. (1998) FEBS Lett. 440, 287-290] by KN-62 caused a further reduction of PLD activity in depolarized synaptosomes. Depolarization-induced inhibition of PLD activity was apparently not due to transmitter release or activation of other kinases. We observed, however, that KCl-induced depolarization caused an increase of inositol phosphates and a reduction of the synaptosomal pool of phosphatidylinositol-4, 5-bisphosphate (PIP(2)). Moreover, in synaptosomes permeabilized with Staphylococcus aureus alpha-toxin, PLD activation induced by calcium was abolished by neomycin, a PIP(2) chelator. We conclude that depolarizing conditions cause an inhibition of neuronal PLD activity which is likely due to breakdown of PIP(2), a required cofactor for PLD activity. Our findings suggest that neuronal PLD activity is regulated by synaptic activity.
Waring
M
M
Department of Pharmacology, University of Mainz, Obere Zahlbacher Str. 67, D-55101, Mainz, Germany.
Drappatz
J
J
Weichel
O
O
Seimetz
P
P
Sarri
E
E
Böckmann
I
I
Kempter
U
U
Valeva
A
A
Klein
J
J
D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D004563:Electrochemistry; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006624:Hippocampus / Q000201:enzymology* / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects; D009355:Neomycin / Q000494:pharmacology; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism; D010739:Phospholipase D / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000502:physiology; D011189:Potassium Chloride / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D013574:Synaptosomes / Q000201:enzymology* / Q000502:physiology; D013997:Time Factors
D004791:Enzyme Inhibitors; D019269:Phosphatidylinositol 4,5-Diphosphate; D011500:Protein Synthesis Inhibitors; D011189:Potassium Chloride; D011493:Protein Kinase C; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D010739:Phospholipase D; D009355:Neomycin