Aim: 

Neurotransmitter (NT) release in neurons is coupled with calcium influx into the presynaptic terminals. In some cases, action of osmotic shock, lanthanides or ruthenium red, calcium-independent exocytosis might be registered. The mechanism of calcium-independent exocytosis remains unexplored.

Methods: 

We have investigated action of lanthanides on exocytosis and D-[³H]Aspartic acid efflux in isolated presynaptic endings (synaptosomes). Exocytosis was determined using fluorescence probe Acridine Orange (AO). Sodium concentration ([Na⁺]_i) was monitored by fluorescent dye Sodium Green and SBFI-AM.

Results: 

Application of 300mkM GdCl₃ increases spontaneous release of D-[³H]Aspartic acid. Experiments with AO reveal GdCl₃ and La(NO₃)₃ induce rapid dose-dependent increase of AO fluorescence intensity indicating exocytosis. Gadolinium blocks calcium channels in neurons. It was shown that P/Q type of calcium channels are raft associated in presynaptic membranes. Gd³⁺ induced exocytosis registered using AO was Ca²⁺ -independent, similar results were obtained with D-[³H]Aspartic acid. Pretreatment of synaptosomes with methyl-betta-cyclodextrin, compound destroying lipid rafts, didn't affect GdCl₃ and La(NO₃)₃ induced D-[³H]Aspartic acid release. Do lanthanides influence any systems downstream Ca²⁺ -sensor? We established that GdCl₃ and La(NO₃)₃ induced an increase of [Na⁺]_i. Enhancement of [Na⁺]_i was not mediated neither by Na⁺ entry via VD channels, as this effect was not prevented by tetrodotoxin, a specific blocker of VD channels nor by lipid rafts.

Conclusions: 

Lanthanides induce Ca²⁺ -independent vesicular release of neurotransmitters via mechanisms common for polyvalent cation.