Patch clamp
The patch is ruptured so the pipette solution exchanges with the cytoplasm and the whole cell is recorded. The standard configuration, at the cost of gradually washing out soluble intracellular contents.
Our ruleSimulations prepare you for the bench but don't replace hands-on practice.
Whole-cell
The patch is ruptured so the pipette solution exchanges with the cytoplasm and the whole cell is recorded. The standard configuration, at the cost of gradually washing out soluble intracellular contents.
How it differs from the standard method
- Low access resistance is essential.
- Cell contents dialyse over minutes.
- Perforated patch keeps them if that matters.
1A glass pipette as an electrode
A fire-polished glass pipette filled with salt solution is pressed gently against a cell. Light suction pulls a patch of membrane into the tip until the glass and the lipid form a seal of several gigaohms, so almost no current leaks between them.
Voltage clamp
The amplifier holds the membrane at a command voltage and reports the current needed to do it: the current through the channels.
Current clamp
The amplifier injects a set current and records the voltage, showing resting potential and action potentials.
The seal
Below about a gigaohm, leak through the seal is bigger than the signal.
2Why access resistance matters so much
Current reaching the cell passes through the narrow pipette tip, whose resistance (the access or series resistance) is typically twice the pipette's own. Any current flowing through it drops voltage: 2 nA through 20 MΩ is 40 mV that the cell never sees.
3Reading the membrane test
A small repeated voltage step gives everything you need to judge a recording: the instantaneous current gives the access resistance, the steady current gives the input resistance, and the decaying transient gives the capacitance, which is proportional to the cell's surface area. Record it at the beginning and end of every cell.
Key terms
Practise these as flashcards →The tight contact between glass and membrane that makes low-noise recording possible.
Resistance between the amplifier and the cell interior, mostly the pipette tip.
Electronics that add back the voltage lost across the access resistance.
The brief current that charges the membrane at the start of a voltage step.
Removing the passive current using scaled small steps (a P/N protocol).
The smallest sustained current that makes a neuron fire.
Correction in current clamp for the voltage drop across the pipette.
When to use it
- Measuring ion channel currents, their voltage dependence and kinetics, or the effect of a drug on them.
- Characterising a neuron's excitability: resting potential, threshold, firing pattern.
- Recording synaptic currents and events in slices or culture.
Compared with alternatives
Multi-electrode arrays record spikes from many cells for hours without breaking into them, but give no subthreshold detail.
Reports activity in many cells at once with far less time resolution than patch clamp.
A biophysics alternative when the question is binding rather than conductance.
Sub-techniques
Choosing one here switches the whole page, including the protocol and the lab, to it.
The patch is ruptured so the pipette solution exchanges with the cytoplasm and the whole cell is recorded. The standard configuration, at the cost of gradually washing out soluble intracellular contents.
- Low access resistance is essential.
- Cell contents dialyse over minutes.
- Perforated patch keeps them if that matters.