Potentiometric measurement of cell volume changes and intracellular ion concentrations in leech Retzius neurones

A potentiometric method to monitor cell volume changes in intact biological tissues is based on ion-selective microelectrodes filled with the classica l K+ exchanger Corning 477317. which is very sensitive to large quaternary ammonium ions. After introduction into a single cell, these cations can be used as volume marker by relating their changes in concentration to changes in cell volume, provided that the ions are neither metabolized nor transpo rted out of the cell. In this article we tested the applicability of this m ethod in leech Retzius neurones. In addition to the cell volume, by using t riple-barreled microelectrodes we also measured simultaneously the intracel lular concentrations of physiologically relevant ion species as well as the membrane potential. We found that Retzius neurones possess an uptake mecha nism which allowed for the intracellular accumulation of tetramethylammoniu m, tetraethylammonium or choline, simply by adding these ions to the bathin g solution. In contrast, tetrapropylammonium was not taken up and therefore , we iontophoretically injected this ion species via conventional microelec trodes. The isoosmotic elevation of the extracellular K+ concentration from 4 to 30 mM (Na+ replaced by K+) induced a swelling of the cells. The chang es in the intracellular concentrations of K+ and Na+ suggest that cell swel ling is primarily due to the uptake of K+, probably with Cl- as counterion. (C) 2001 Elsevier Science Ltd. All rights reserved.