Intracellular Ion Activity (K+ Ca2+ and Cl-) and Membrane Potential of Frog Muscle in Vitro

Dufau et al. (3) decribed a double-barrel ion-sensitive microelectrode (ISME) with an extra thin tip diameter (0.1/um) developed for the simultaneous measurement of intracellular ion activity and membrane potential. As the measurements performed with these electrodes had yielded extremely low membrane potentials in cells in tissue culture (1), we decided to test the accuracy of the electrodes with measurements of intracellular K+, Ca2+ and Cl- activities of frog muscle, where the membrane potential and ion concentration are known.