Discontinuous volume transitions induced by calcium–sodium ion exchange in anionic gels and their neurobiological implications

Discontinuous volume transitions in poly (acrylic acid) gels were studied by determining equilibrium swelling curves of small gel beads immersed in salt solutions containing varying concentrations of Ca2+ and Na+. Reversible contractions of gel membranes associated with Ca(2+)-Na+ exchange were examined using both isometric and isotonic recording devices. A discontinuous change in electric conductance was demonstrated in association with Ca(2+)-Na+ exchange in gel membranes. These experimental findings provide a sound physicochemical basis for elucidating the mechanism of nerve excitation.