Electrophoresis of Cytoplasmic Molecules Through Gap Junctions by Externally Applied Electric Fields

¹ Howard Hughes Medical Institute, Yale University School of Medicine, Section of Molecular Neurobiology, New Haven, Connecticut 06510
² Department of Zoology, University of California, Berkeley, California 94720
³ Department of Physiology and Biophysics, University of California, Irvine, California 92717

External electric fields are efficiently conducted into the cytoplasmic interior of extended chains of cells that are electrotonically coupled by gap junctions. For chains of cells or tissues that are much longer than their electrical length constant, the cytoplasmic electric field within the center of the ensemble is identical in magnitude to the externally applied field. Over a period of time, this internal electric field should cause a intercellular redistribution of charged molecules that are permeant to gap junctions, within the coupled tissue. This prediction was confirmed experimentally by observing the directed migration of 6-carboxyfluorescein (negatively charged) within the electrotonically coupled lateral giant neurons of a crayfish nerve cord under the influence of externally applied DC electric fields. To determine whether such redistributions could occur in developing epithelial tissues, hydra were exposed to DC electric fields, after charged fluorescent dyes had been loaded into their ectoderm. In this electrotonically coupled tissue, the fluorescent dyes also underwent an electrophoretic redistribution in response to externally applied fields. To facilitate the future use of electric fields as an experimental means to redistribute intracellular constituents in developing tissues, mathematical relationships are presented that predict the time course and steady-state concentration profiles of molecules under-going intercellular electrophoresis.