VC and IC Modes
Voltage-clamp and current-clamp whole-cell recording configurations

One of the most fundamental concepts in whole-cell patch-clamp technique is the distinction between voltage-clamp configuration and current-clamp configuration (often abbreviated VC and IC).

Current Clamp Configuration (IC mode)

  • IC mode reports the voltage of the neuron.
  • In IC mode, the voltage of the neuron can swing up and down depending on the currents that occur naturally (through ion channels in the membrane) or in response to current delivered through the pipette.
  • If enough positive current is applied to allow the neuron’s voltage to pass the AP threshold voltage, it will begin to fire. The more current is applied, the faster the neuron will fire.
  • When no current is applied through the patch pipette (0 pA of applied current), it is in “listening mode” where it only records the voltage of the cell as it behaves physiologically. This is often called I=0 mode.
  • Excitatory and inhibitory currents in IC mode appear as EPSPs and IPSPs.
  • Inward (excitatory) currents (such as EPSCs) appear as upward deflections in voltage.

Voltage Clamp Configuration (VC mode)

  • VC mode reports the current required to clamp the voltage at a particular voltage.
  • In VC mode, the neuron’s voltage does not change.
  • Excitatory currents and inhibitory currents in IC mode appear EPSCs and IPSCs.
  • Inward (excitatory) currents (such as EPSCs) appear as downward deflections in current.
  • VC mode is ideal for measuring currents through ion channels of the neural membrane.
  • Action potentials will never be observed in VC mode (since VC mode holds the cell at a fixed voltage).