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Abstract
Newly synthesized phosphatidylinositol phosphates have been implicated in many membrane-trafficking reactions. They are essential for exocytosis of norepinephrine in PC12 cells and chromaffin cells, suggesting a function in membrane fusion. We have now studied the role of phosphatidylinositol phosphates in synaptic vesicle exocytosis using synaptosomes. Under conditions where phosphorylation of phosphatidylinositols is blocked, norepinephrine secretion was nearly abolished whereas glutamate and GABA release was still elicited. Thus phosphatidylinositides are essential only for some membrane fusion reactions, and exocytotic release mechanisms differ between neurotransmitters.
Highlights
At synapses, similar mechanisms of synaptic vesicle exocytosis are thought to effect the secretion of different neurotransmitters
We tested the effect of phenylarsine oxide (PAO) on PIP and PIP2 synthesis in synaptosomes
Our data show that norepinephrine secretion elicited with four stimulation protocols is severely inhibited by PAO
Summary
Similar mechanisms of synaptic vesicle exocytosis are thought to effect the secretion of different neurotransmitters (e.g. glutamate, GABA,1 and norepinephrine; reviewed in Refs. 1– 4). To test the effect of PAO on release, synaptosomes were treated with PAO in Me2SO, Me2SO alone (control; Ͻ1% of total volume), or vanadyl hydroperoxide (VOOH; prepared as a complex with 1,10-phenanthroline as in Ref. 22) for 20 min at 35 °C in Ca2ϩ-containing aerated (95% O2, 5% CO2) Krebs-bicarbonate buffer. To control for this and other possible indirect effects, we performed experiments in which synaptosomes were first loaded with 3H-labeled neurotransmitters and treated with PAO, with identical results to those shown here.
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