Indirect Measurement of Intracellular Conductivity

The apparent resistance of a fluid-filled micropipette depends upon the conductivity of the fluid in which its tip-is immersed. When the electrode is involved in the determination of the impedance of cell membranes, then the intracellular conductivity must be known. Techniques used in large cells require extrusion of intracellular fluid or the simultaneous insertion of two or more electrodes in a single cell, and are not feasible for small cardiac cells. We present an indirect method in which. two unlike electrodes are inserted individually into distinct cells of a given type. The difference in measured resistances is independent of the membrane impedance, and can be calibrated by immersion in a sequence of fluids of known conductivities.