Accurate measurement of junctional conductance between electrically coupled cells with dual whole-cell voltage-clamp under conditions of high series resistance

Accurate measurement of the junctional conductance (Gj) between electrically coupled cells can provide important information about the functional properties of coupling. With the development of tight-seal, whole-cell recording, it became possible to use dual, single-electrode voltage-clamp recording from pairs of small cells to measure Gj. Experiments that require reduced perturbation of the intracellular environment can be performed with high-resistance pipettes or the perforated-patch technique, but an accompanying increase in series resistance (Rs) compromises voltage-clamp control and reduces the accuracy of Gj measurements. Here, we present a detailed analysis of methodologies available for accurate determination of steady-state Gj and related parameters under conditions of high Rs, using continuous or discontinuous single-electrode voltage-clamp (CSEVC or DSEVC) amplifiers to quantify the parameters of different equivalent electrical circuit model cells. Both types of amplifiers can provide accurate measurements of Gj, with errors less than 5% for a wide range of Rs and Gj values. However, CSEVC amplifiers need to be combined with Rs-compensation or mathematical correction for the effects of nonzero Rs and finite membrane resistance (Rm). Rs-compensation is difficult for higher values of Rs and leads to instability that can damage the recorded cells. Mathematical correction for Rs and Rm yields highly accurate results, but depends on accurate estimates of Rs throughout an experiment. DSEVC amplifiers display very accurate measurements over a larger range of Rs values than CSEVC amplifiers and have the advantage that knowledge of Rs is unnecessary, suggesting that they are preferable for long-duration experiments and/or recordings with high Rs.