Ca²⁺ influx slows single synaptic vesicle endocytosis

Area of Science:

• Neuroscience
• Cell Biology
• Biochemistry

Background:

• Synaptic vesicle recycling is crucial for neurotransmission.
• Distinguishing Ca²⁺ roles in vesicle fusion and retrieval is challenging.
• Previous studies relied on bulk measurements, obscuring single-vesicle dynamics.

Purpose of the Study:

• To dissect the distinct roles of Ca²⁺ in synaptic vesicle fusion and retrieval.
• To investigate Ca²⁺ regulation of single synaptic vesicle recycling dynamics.
• To identify molecular mechanisms underlying Ca²⁺-mediated effects on vesicle recycling.

Main Methods:

• Utilized a pHluorin-tagged vesicular probe for monitoring single synaptic vesicle recycling.
• Employed rat hippocampal neurons for ex vivo studies.
• Applied Ca²⁺ chelators (EGTA) and specific inhibitors (FK506) to probe molecular pathways.

Main Results:

• Ca²⁺ significantly increases synaptic vesicle fusion probability.
• Ca²⁺ unexpectedly decreases the rate of synaptic vesicle retrieval.
• Inhibition of calcineurin or Ca²⁺ chelation prevents the Ca²⁺-induced decrease in retrieval rate.
• Repetitive neuronal activity shows a progressive decrease in vesicle retrieval, consistent with Ca²⁺-mediated inhibition.

Conclusions:

• Ca²⁺ entry during action potentials differentially regulates synaptic vesicle fusion and retrieval.
• Ca²⁺ acts as a negative regulator of synaptic vesicle retrieval rate.
• Calcineurin is implicated in the Ca²⁺-dependent suppression of synaptic vesicle recycling.