A supercharger for single electrode voltage and current clamping

The theory and several circuits for supercharging is described for single micro and patch electrode voltage and current clamping. Supercharging is of use where the charging time of the cell membrane capacity results in the membrane potential change to considerably lag behind the command potential. This membrane capacity charging time is dependent on the series electrode resistance, the membrane resistance and capacity. Thus although amplifier voltage response times may be in microseconds, the membrane potential response to a step command potential often requires several milliseconds. Supercharging overcomes this difficulty by accelerating the membrane capacity charging time by applying a large initial and brief supercharging or 'booster' potential or current, to the command signal. Supercharging can improve membrane potential rise times by more than a hundred and thus bring membrane potentials to a stationary state well under a millisecond. Early changes in membrane properties are thus more readily observed during voltage and current clamping without being masked by capacitive currents. This technique also provides for the measurement of membrane time constants. The circuitry described is a simple add-on to the command signal pathway, is easy to adjust and provides the appropriate supercharging potentials for sequential step command signals of different amplitudes.