Occlusion of hippocampal electrical junctions by intracellular calcium injection

Low-molecular weight dyes such as Lucifer yellow or carboxyfluorescein have been used to investigate the electrical connectivity of neurons via gap junctions. The interpretation that such dye passage is mediated through intercellular channels has been controversial and difficult to corroborate with direct techniques in mammalian brain. We report here that elevated intracellular free Ca²⁺, a treatment shown to cause gap junction occlusion in other tissues, significantly blocks dye transfer between hippocampal cells. Furthermore, intracellular injection of FITC-dextran (which is too large to cross gap junctions) never resulted in multiple hippocampal cell fills. These data lend strong support to the argument that the extent of dye-coupling provides a good estimate of the number of intercellular communication channels, and raises the possibility that these channels may be physiologically modulated.