RAPID VOLUME EXPANSION IN THE TORPEDO ELECTRIC ORGAN ASSOCIATED WITH ITS POSTSYNAPTIC POTENTIAL

By electrically stimulating Torpedo electric organs enclosed in a seal ed plastic chamber, it was demonstrated that the production of a posts ynaptic 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. Re petitive stimulation produced a summation of volume changes. The maxim um change evoked by a single electric shock was roughly 10(-6) times t he electrocyte volume. The thermal expansion of the organ associated w ith 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 elec trocyte protoplasm may be at the base of the volume changes. (C) 1997 Academic Press.