Continuous single electrode voltage-clamp (cSEVC) is an electrophysiological patch-clamping method to pass a membrane voltage into a cell and measure the change in current as the voltage steps. In cSEVC, the same electrode is used simultaneously for voltage recording and for current passing. The cSEVC circuit is illustrated as a voltage source (Vcmd) in series with the effective access resistance (Ra.eff) and the membrane (Rm, Cm). The cSEVC circuit ensures that the pipette potential (Vp) is equal to Vcmd.
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Vcmd = Voltage source or command voltage
Vp = Pipette potential
Ra,eff = Effective access resistance
Im = Current across the membrane
Vm = Membrane voltage
Cm = Membrane capacitance
Rm = Membrane resistance
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After Vcmd steps to V1, a stead-state current (Im) flows in the circuit. The membrane potential is equal to Vcmd - Im Ra,eff. After the step change in the command potential, Im and Vm settle exponentially to their steady state values with the time constant τ. In general, Rm >> Ra,eff, a good approximation is τ ≈ Ra,effCm.
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Vcmd = Command voltage
V1 = Voltage step
Ra,eff = Effective access resistance
Im = Steady state current
Vm = Membrane voltage
Cm = Membrane capacitance
Rm = Membrane resistance
Vm1 = Membrane potential at V1
τ = Time constant
IRf = Current through the membrane resistance
I1 = Current
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