Electrokinetic properties of isolated cerebral-cortex synaptic vesicles

Area of Science:

• Neuroscience
• Biochemistry
• Physical Chemistry

Background:

• Synaptic vesicles are crucial for neurotransmission.
• Understanding their surface properties is key to synaptic function.
• Electrokinetic properties provide insights into surface charge and composition.

Purpose of the Study:

• To characterize the electrokinetic properties of guinea-pig cerebral cortex synaptic vesicles.
• To identify the molecular components contributing to the synaptic vesicle surface charge.
• To compare synaptic vesicle surface properties with synaptosomal membranes.

Main Methods:

• Electrophoretic mobility measurements in varying pH and ionic strength.
• Enzymatic treatments (neuraminidase, trypsin, RNase, DNase, chondroitinase ABC, hyaluronidase).
• Cation binding studies (Mn2+, Ca2+, Mg2+, Sr2+, Ba2+).

Main Results:

• Synaptic vesicles exhibited a negative electrophoretic mobility (-3.55 µm.s⁻¹.V⁻¹.cm) at pH 7.2.
• Mobility was pH and ionic strength dependent, suggesting weak acidic groups (pKa 3.0-3.8).
• Trypsin and concanavalin A treatments increased mobility; sialic acid did not significantly contribute. Divalent cations (Mn2+, Ca2+) reduced mobility more than others.

Conclusions:

• The synaptic vesicle surface is negatively charged due to weak acidic functional groups.
• Specific proteins, not sialic acid, significantly influence synaptic vesicle electrokinetic properties.
• These findings provide insights into synaptic vesicle surface composition and interactions relevant to neurotransmission.