Phenylarsine oxide is able to dissipate synaptic vesicle acidic pool

Abstract

Phenylarsine oxide (PAO) has a number of targets in the neurons, one of them is exocytotic process. In this study, we have focused on the mechanisms of phenylarsine oxide action on Ca 2+-dependent and Ca 2+-independent neurotransmitter release from rat brain synaptosomes. We investigated the influence of phenylarsine oxide on: (i) l-[ 14C]glutamate and [ 3H]GABA release and uptake; (ii) plasma membrane potential using a potential-sensitive fluorescent probe rhodamine 6G; (iii) exo/endocytotic process using a pH-sensitive fluorescent probe acridine orange (AO). It has been found that phenylarsine oxide induced deacidification of synaptic vesicles. This effect was completely abolished by preliminary treatment of synaptosomes with a protonophore FCCP indicating that both reagents injured a proton electrochemical gradient. Dissipation of the proton gradient by low concentrations of phenylarsine oxide (not exceed 1 μM) did not prevent KCl-triggered exocytotic response, but essentially modified endocytotic one. At higher concentrations of phenylarsine oxide (up to 10 μM), the proton gradient dissipation was intensified and the exocytotic response was fully abolished. The reagent did not change plasma membrane potential, but depolarized mitochondria. It also caused potent inhibition of the Ca 2+-stimulated l-[ 14C]glutamate and [ 3H]GABA release and increase the Ca 2+-independent release of l-[ 14C]glutamate, but not of [ 3H]GABA. Disulfide-reducing reagents (dithiothreitol and β-mercaptoethanol) completely prevented phenylarsine oxide-evoked injuries. They could also restore the initial levels of the mitochondrial potential, the exocytotic response to KCl and the release and uptake of neurotransmitters. Our data provide the evidence that phenylarsine oxide causes dissipation of synaptic vesicle acidic pool resulting in the reduction of vesicle filling and as consequence in attenuation of Ca 2+-stimulated neurotransmitter release.