Substructure and responses of cholinergic synaptic vesicles in the atomic force microscope

Area of Science:

• Biophysics
• Neuroscience
• Materials Science

Background:

• Synaptic vesicles are crucial for neurotransmission, but their structural integrity under varying conditions is not fully understood.
• Understanding vesicle substructure and response to osmotic stress provides insights into cellular membrane dynamics.

Purpose of the Study:

• To investigate the substructure and osmotic stress responses of individual synaptic vesicles using atomic force microscopy (AFM).
• To characterize the morphological changes of cholinergic synaptic vesicles from Torpedo californica under decreasing osmolarity.

Main Methods:

• Utilized tapping mode atomic force microscopy (AFM) to image 100-nm cholinergic synaptic vesicles.
• Continuously imaged vesicles while decreasing buffer osmolarity.
• Employed phase mode AFM to analyze the surface characteristics of intact and lysed vesicles.

Main Results:

• Synaptic vesicles lysed in hyposmotic buffer, forming flat circular structures approximately twice the diameter of intact vesicles.
• The lysed structures had a thickness of 7.2 +/- 1.7 nm, accommodating the lipid bilayer and internal proteoglycan.
• AFM imaging revealed membrane creases on intact vesicles and the presence of released intravesicular proteoglycan on lysed vesicles.

Conclusions:

• Synaptic vesicles exhibit significant structural changes in response to osmotic stress, including lysis and release of internal contents.
• AFM is effective in visualizing nanoscale structural details and dynamic responses of synaptic vesicles.
• The findings suggest a mechanism for proteoglycan release from synaptic vesicles under low osmotic and ionic strength conditions.