Definition of physical integrity of synaptosomes and myelosomes by enzyme osmometry.

Isotonic requirements for synaptosomes were shown to vary with the concentration of sucrose or mannitol in the isolation medium, as well as with their differential permeability to polyols and ions. The technique of enzyme osmometry, which permits quantitation of the osmotic integrity in a heterogeneous population, was used to defined the osmotic requirements for synaptosomes and myelosomes in a variety of ionic and nonelectrolyte media. Important differences, observed in the rank order of permeability of synaptosomal and myelosomal membranes to electrolyte media, were consistent with the known channel density/electrical activity of the corresponding plasma membranes.