A digitally-modulated conductance clamp eliminates instability observed with larger current signals in conventional dynamic clamp.

Abstract

Stability measurements in artificial cells showed that large simulated electrical signals generated via dynamic clamp coupled with small cell capacitances leads to electrical oscillations. These oscillations deteriorate cell membranes leading to instability and early termination of electrophysiological recording in living cells. We designed a Digitally-Modulated Conductance Clamp module that eliminates this instability observed in dynamic clamp systems. The module uses faster analog circuitry to calculate the simulated electrical signals instead of slower all-digital calculations. As a Proof-of-Concept, we simulated cardiac action potentials (APs) at four capacitances and four resistances. The stability of the cardiac AP was monitored with increasing digital INa and analog INa current levels. Instability was monitored in the Phase I (‘spike’) region of the simulated cardiac AP and defined as at least one sweep with oscillations or ‘ringing’ in 10 sweeps. We observed instability with increasing INa levels and no instability with increasing analog INa levels. For example, at a capacitance of 24.9±0.3 pF and a resistance of 11.2±0.2 mΩ, instability was observed at a mean digital INa current of −1420±90 pA (at −40 mV) (n=5) whereas at the same capacitance/resistance values, no instability was observed at the maximum analog INa current of −6810 pA at −40 mV. Our findings reveal the limitation of dynamic clamp when calculating larger currents using slower digital calculations via software. INa generated using the Digitally-Modulated Conductance Clamp module allowed for larger currents with no instability observed in the simulated cardiac APs. Larger simulated electrical signals generated via dynamic clamp can now be input into living cells with the faster analog circuitry eliminating the electrical oscillations and instability.