Rapid volume expansion in the Torpedo electric organ associated with its postsynaptic potential

By electrically stimulating Torpedo electric organs enclosed in a sealed plastic chamber, it was demonstrated that the production of a postsynaptic potential is accompanied by a rapid increase in the volume of the organ. This increase started almost simultaneously with the onset of the postsynaptic potential and reached its maximum at about the end of the potential. The volume returned slowly to its resting level. Repetitive stimulation produced a summation of volume changes. The maximum change evoked by a single electric shock was roughly 10(-6) times the electrocyte volume. The thermal expansion of the organ associated with the production of a postsynaptic potential accounts for roughly 25% or less of this volume increase. The possibility is pointed out that a cation-exchange process involving Ca2+ on anionic sites in the electrocyte protoplasm may be at the base of the volume changes.