Bioelectrical Measurements

Abstract

Bioelectrical measurements include the determination of potential differences, measurements of the electrical parameters of membranes, and, occasionally, the measurement of ionic fluxes as currents in circuits. Of these, the determination of the resting potential differences is perhaps the most fundamental in transport studies. Data on the potential differences across membranes make it possible to evaluate the total driving force acting on individual ion species so that criteria of the character of the ion transport like the Ussing-Teorell flux ratio may be applied. In a steady state even a simple comparison of the electrical potential difference with the equilibrium potential calculated from the concentrations of the ion on both sides of the membrane may be sufficient for deciding whether the ion is actively transported or not. Although very often performed, the measurements of the potential differences are not quite free of theoretical objections. It was well said by Gibbs that “Again, the consideration of the electrical potential in the electrolyte, and especially the consideration of the difference of potential in electrolyte and electrode, involve the consideration of quantities of which we have no apparent means of physical measurement, while the difference of potential in pieces of metal of the same kind attached to the electrodes is exactly one of the things which we can and do measure,” (Gibbs, 1899, quoted by Guggenheim, 1967).