Isolation of synaptic junctional complexes of high structural integrity from rat brain

Area of Science:

• Neuroscience
• Cell Biology
• Biochemistry

Background:

• Synaptic junctional complexes (SJC) are crucial for neuronal communication.
• Previous methods for SJC isolation often resulted in compromised structural integrity.

Purpose of the Study:

• To develop and validate a new method for isolating highly structured synaptic junctional complexes (SJC).
• To characterize the biochemical and structural properties of the isolated SJCs.

Main Methods:

• Homogenization of synaptosomal membrane (SM) fraction in a biphasic Freon 113 and Triton X-100 aqueous system.
• Isolation of SJCs using low-speed centrifugation and discontinuous sucrose density gradient centrifugation.
• Purity and identity assessment via electron microscopy and enzyme activity assays.
• Polypeptide composition analysis using SDS-PAGE.

Main Results:

• The new method successfully isolated well-preserved SJCs with high structural integrity.
• Electron microscopy confirmed SJCs constitute approximately 65% of the isolated fraction's structures.
• Enzyme activities (Na, K-ATPase, cytochrome oxidase, acid phosphatase) showed partial but not total inactivation.
• SDS-PAGE revealed tubulin as the major polypeptide, with actin also present in the SJC-enriched fraction.

Conclusions:

• The Triton-Freon biphasic system is effective for isolating high-purity synaptic junctional complexes.
• The isolated SJCs retain significant structural and biochemical characteristics.
• The SJC fraction is enriched in tubulin and contains actin, providing insights into synaptic structure.