Switched single-electrode voltage-clamp amplifiers allow precise measurement of gap junction conductance

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Abstract
Measurement of gap junction conductance (gj) with patch-clamp amplifiers can, due to series resistance problems, be subject to considerable errors when large currents are measured. Formulas developed to correct for these errors unfortunately depend on exact estimates of series resistance, which are not always easy to obtain. Discontinuous single-electrode voltage-clamp amplifiers (DSEVCs) were shown to overcome series resistance problems in single whole cell recording. With the use of two synchronized DSEVCs, the simulatedgj in a model circuit can be measured with a maximum error of gj, 1–100 nS). At a very lowgj of 100 pS, the error sometimes exceeded 5% (maximum of 15%), but the error was always 100 MΩ. The precision of the measurements is independent of series resistance, membrane resistance, andgj. Consequently, it is possible to calculategj directly from Ohm’s law, i.e., without using correction formulas. Our results suggest that DSEVCs should be used to measuregj if large currents must be recorded, i.e., if cells are well coupled or if membrane resistance is low.