Determination of ζ-Potential in Rat Organotypic Hippocampal Cultures

ζ-potentials of entities such as cells and synaptosomes have been determined, but ζ of brain tissue has never been measured. Electroosmotic flow, and the resulting transport of neuroactive substances, would result from naturally occurring and experimentally or clinically induced electric fields if ζ is significant. We have developed a simple method for determining ζ in tissue. An electric field applied across a rat organotypic hippocampal slice culture (OHSC) drives fluorescent molecules through the tissue by both electroosmotic flow and electrophoresis. Fluorescence microscopy is used to determine each molecule's velocity. Independently, capillary electrophoresis is used to measure the molecules’ electrophoretic mobilities. The experiment yields ζ-potential and average tissue tortuosity. The ζ-potential of OHSCs is −22 ± 2 mV, and the average tortuosity is 1.83 ± 0.06. In a refined experiment, ζ-potential is measured in various subregions. The ζ-potentials of the CA1 stratum pyramidale, CA3 stratum pyramidal, and dentate gyrus are −25.1 ± 1.6 mV, −20.3 ± 1.7 mV, and −25.4 ± 1.0 mV, respectively. Simple dimensional arguments show that electroosmotic flow is potentially as important as diffusion in molecular transport.