Effects of calcium-containing fixation solutions on cholinergic synaptic vesicles

Area of Science:

• Neuroscience
• Cell Biology
• Biochemistry

Background:

• Cholinergic synaptic vesicles are crucial for neurotransmission.
• The role of calcium in synaptic vesicle dynamics is not fully understood.
• Electric organs provide a model system for studying nerve terminal structure and function.

Purpose of the Study:

• To investigate the ultrastructural effects of calcium-containing fixation solutions on cholinergic synaptic vesicles.
• To elucidate the role of calcium in synaptic vesicle morphology and membrane interactions.
• To identify potential sites of newly synthesized acetylcholine within nerve terminals.

Main Methods:

• Fixation of electric organ slices from Narcine brasiliensis using calcium-containing solutions.
• Electron microscopy of unosmicated, unstained tissues.
• Use of Ca-chelating agents to assess the nature of electron-dense particles.
• Analysis of vesicle membrane morphology and fusion events with the terminal membrane.

Main Results:

• Calcium (Ca) forms electron-dense particles within vesicles, suggesting Ca binding.
• Vesicle membranes exhibit 'crinkling' or collapse, reversible by Ca removal.
• Calcium induces vesicle fusion with the terminal membrane, providing morphological evidence for Ca-facilitated exocytosis.

Conclusions:

• Calcium binds to synaptic vesicles, potentially via ATP, influencing their structure.
• Calcium-induced vesicle fusion at the terminal membrane may represent the storage site for newly synthesized acetylcholine.
• These findings offer ultrastructural insights into calcium's role in neurotransmitter release.