Summary
Concentration-step experiments with epithelial membranes can be done in the voltage clamp mode if the clamp circuit is sufficiently fast and changes of resistivity of the flowing solution are compensated for automatically. The electronic system developed for this purpose changes in regular intervals for 30 ms from the fast voltage clamp mode to a “mixed clamp” mode. In this state it works as a voltage clamp with respect to low frequencies, but as a current clamp with respect to high frequencies. It records the solution resistanceR b in series to the membrane(s) as a 100kH impedance and stores it for the interval between “mixed clamp” periods, i.e. during the fast voltage clamp mode. The stored value ofR b is multiplied with the instantaneous value of the clamp current,I, by means of a multiplying AD-converter. The product is continuously subtracted from the measured “membrane”-voltage. Thus, settling time and steady state accuracy of the clamp are improved considerably and become almost independent of changes inR b . Manual adjustments during the experiment are not required.
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References
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Supported by the DFG through Sonderforschungsbereich 38, project C1.
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Gebhardt, U. A fast voltage clamp with automatic compensation for changes of extracellular resistivity. Pflugers Arch. 347, 1–7 (1974). https://doi.org/10.1007/BF00587049
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DOI: https://doi.org/10.1007/BF00587049