Dielectric properties of synaptosomes isolated from rat brain cortex

Dielectric measurements were performed on the suspensions of synaptosomes isolated from rat brain cortex. The synaptosomes in buffered salt media showed typical dielectric dispersions caused by the presence of a thin limiting membrane of sufficiently low conductivity. An analysis of the dielectric data revealed that the electric conductivity of the synaptosome interior was about 37 % of the external medium conductivity under isotonic conditions and that the dielectric constant for the interior phase was about 35. The membrane capacitance (0.7 ΜF cm⁻²) remained constant irrespective of nature and concentration of the univalent salts examined. Significant reduction in both the conductivity and the dielectric constant of the internal phase can be explained theoretically provided that some intra-synaptosomal structure (synaptic vesicles and/or small mitochondria) of non-conducting nature occupies about 50 % of the particulate volume, the remainder being in equilibrium with the external salt medium.