Patch clamp electrophysiology is the gold-standard technique for studying ion channel function. It measures the electrical current flowing through ion channels in cell membranes with picoampere sensitivity and millisecond temporal resolution. The technique was developed by Neher and Sakmann, who received the Nobel Prize in 1991.
The patch clamp technique uses a glass micropipette with a tip diameter of approximately 1 µm, filled with electrolyte solution and containing a silver-silver chloride electrode. The pipette is pressed against the cell membrane, and gentle suction forms a gigaohm seal between the glass and the membrane. This high-resistance seal reduces electrical noise and allows measurement of picoampere currents.
The cell-attached configuration records currents from channels in the intact membrane patch while leaving the cell interior undisturbed. The inside-out patch is formed by retracting the pipette from the cell, exposing the intracellular membrane surface to the bath solution. This configuration allows control of the intracellular environment. The outside-out patch is formed by breaking the seal and then retracting the pipette, causing membrane to reform with the extracellular surface facing the bath. This configuration is used for studying channel pharmacology.
Whole-cell patch clamp breaks the membrane patch by applying suction or voltage pulses, providing electrical access to the cell interior. The pipette solution dialyzes the cytoplasm, allowing control of the intracellular ionic composition. Perforated patch variants use antibiotics such as amphotericin B to maintain electrical access without cytoplasmic dialysis.
The voltage clamp mode holds the membrane potential at a commanded value and measures the current required to maintain that potential. Current-voltage relationships reveal the voltage dependence of channel activation and rectification. The current clamp mode injects current and measures the resulting membrane potential changes, recording action potentials and synaptic potentials involved in cell signaling.
Data analysis includes determination of single-channel conductance, open probability, mean open and closed times, and the effects of modulators. Drugs are applied using rapid solution exchange systems for studying kinetics. Temperature control maintains physiological conditions.
Automated patch clamp systems using planar electrode chips enable medium-throughput screening of ion channel drugs. These systems are used in pharmaceutical development for safety pharmacology assessment of hERG channel liability and for discovery of novel channel modulators.
