Isolation of postsynaptic densities retaining their membrane attachment.

Area of Science:

• Neuroscience
• Cell Biology
• Biochemistry

Background:

• Postsynaptic densities (PSDs) are crucial organelles in neuronal synapses, but their function remains largely unknown.
• Previous methods for isolating PSDs often involved detergents, which could disrupt their structure and associated membranes.
• A practical method for isolating intact PSDs, preserving the postsynaptic membrane, was needed for further research.

Purpose of the Study:

• To develop a detergent-free method for isolating intact postsynaptic units from rat cerebral cortex.
• To characterize the biochemical and morphological integrity of the isolated postsynaptic units.
• To assess the utility of the preparation for studying molecular interactions at the postsynaptic membrane.

Main Methods:

• Chemical dissociation of the synaptic cleft followed by sonication of extracted membranes.
• Separation of postsynaptic units on a discontinuous sucrose gradient.
• Biochemical analysis of protein composition and binding assays (e.g., spiroperidol).

Main Results:

• A postsynaptic unit preparation (30-50% purity) was successfully isolated without detergents.
• The preparation demonstrated enhanced binding of spiroperidol, a dopamine agonist.
• Morphological and biochemical analyses confirmed the integrity of the postsynaptic membrane associated with the PSD.
• Major proteins identified include actin, alpha- and beta-tubulin, and postsynaptic density protein.

Conclusions:

• This novel method provides the first practical procedure for isolating intact postsynaptic units, preserving the postsynaptic membrane.
• The preparation's integrity allows for studying the interaction between the postsynaptic membrane and PSD.
• The isolated units are suitable for various localization studies, including ion-translocating ATPases and protein kinases.