Dopamine neurons release transmitter via a flickering fusion pore

Abstract

A key question in understanding mechanisms of neurotransmitter release is whether the fusion pore of a synaptic vesicle regulates the amount of transmitter released during exocytosis. We measured dopamine release from small synaptic vesicles of rat cultured ventral midbrain neurons using carbon fiber amperometry. Our data indicate that small synaptic vesicle fusion pores flicker either once or multiple times in rapid succession, with each flicker releasing approximately 25-30% of vesicular dopamine. The incidence of events with multiple flickers was reciprocally regulated by phorbol esters and staurosporine. Thus, dopamine neurons regulate the amount of neurotransmitter released by small synaptic vesicles by controlling the number of fusion pore flickers per exocytotic event. This mode of exocytosis is a potential mechanism whereby neurons can rapidly reuse vesicles without undergoing the comparatively slow process of recycling.

Somatodendritic dopamine release: recent mechanistic insights

“…Indeed, somatodendritic vesicles are sparse and appear to be insufficient in number to provide an adequate source of DA for vesicular exocytotic release. Nevertheless, there is evidence for quantal DA release from DA somata in the SNc, with an estimated quantal size of 14 000 molecules per vesicle [70], which is of similar magnitude to that determined for release from chromaffin granules [111], as well as from axonal varicosities of DA neurons in culture [112,113]. Second, primary storage of somatic DA in both SNc and VTA appears to be in 'tubulovesicles' (saccules of smooth endoplasmic reticulum (ER)) that express VMAT2, although VMAT2 is also associated with occasional small clear vesicles or large dense core vesicles [78].…”

α-Synuclein – Regulator of Exocytosis, Endocytosis, or Both?

“…Kiss-and-run endocytosis is also known as 'flicker-fusion' because the synaptic vesicle does not fully collapse upon membrane fusion, and instead the neurotransmitter is released through a small fusion pore. In dopaminergic neurons, the neurons vulnerable in Parkinson's disease, kiss-and-run-mediated exocytosis has been clearly shown [58,59]. However, in hippocampal neurons some studies argue that clathrin-mediated endocytosis is the main or even the only mechanism [54], while others report up to 60% of kiss-and-run endocytosis [60].…”

Revisiting oxidative stress and mitochondrial dysfunction in the pathogenesis of Parkinson disease—resemblance to the effect of amphetamine drugs of abuse

“…Under normal conditions, dopamineis synthesized from tyrosine by tyrosine hydroxylase (TH), the rateͲlimiting enzyme in dopamine biosynthesis, and aromatic amino acid decarboxylase. Once formed, dopamineis safely stored in high millimolar concentrations in synaptic vesicles following uptake by VMAT2 [118]. Impairment of vesicular storage of dopamine, which may be due to the presence of alphaͲsyn protofibrils, oxidative stress or weak base compounds such as methamphetamine(further describedbelow) [119], leads to increased dopaminelevels in the cytoplasm.…”