[Osmotic properties of heavy and light synaptosomes of the rat cerebral cortex]

A comparison has been carried out of osmotic properties of light and heavy synaptosomal fractions and a mitochondrial fraction from the rat brain cortex. A critical change is the rate of swelling at a definite time, allowing to subdivide the process into two phases, was shown. Throughout the swelling, its rate for heavy synaptosomes and mitochondria was much higher than that for the light ones. According to the initial rate of swelling in isoosmotic glycerol, the fractions examined can be arranged in the following order: mitochondria < light synaptosomes < heavy synaptosomes. Both total, light and heavy synaptosomes reveal the properties of ideal osmometers. The osmotic properties of synaptosomes and mitochondria are largely dependent on pH of the medium: with a shift towards acidic values of pH the swelling rate decreases to increase at more alkaline values. Especially well-pronounced changes occur at pH 6.8 and pH 7.3.