Axon Instruments Patch-Clamp Amplifiers

Current Clamp Amplifier

Current-clamp is a method used to measure the resulting membrane potential (voltage) from an injection of current. To measure the membrane potential, the MultiClamp 700B and Axoclamp 900A both monitor voltage drop initiated by current injection along an in-series resistor. Current-clamp is commonly used to inject simulated, but realistic current waveforms into a cell, and monitor membrane effect. This technique is ideal for the evaluation of important cellular events such as action potentials.

Electrophysiology

Electrophysiology is the field of research studying current or voltage changes across a cell membrane. Electrophysiology techniques are widely used across a diverse range of neuroscience and physiological applications; from understanding the behavior of single ion channels in a cell membrane, to whole-cell changes in the membrane potential of a cell, to larger scale changes in field potential within the brain slices in vitro or brain regions in vivo.

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Ion Channels

An ion channel is a group of proteins that form a pore across the lipid bilayer of a cell. Each channel is permeable to a specific ion (examples: potassium, sodium, calcium, chloride). Patch-clamp is used to evaluate current or voltage in the membrane associated with ion channel activity via direct measurement in real time using ultra-sensitive amplifiers, high-quality data acquisition systems, and powerful software to evaluate the results.

Patch Clamp

The patch-clamp technique involves a glass micropipette forming a tight gigaohm (GΩ) seal with the cell membrane. The micropipette contains a wire bathed in an electrolytic solution to conduct ions. The whole-cell technique involves rupturing a patch of membrane with mild suction to provide low-resistance electrical access, allowing control of transmembrane voltage. Alternatively, investigators can pull a patch of membrane away from the cell and evaluate currents through single channels via the inside-out or outside-out patch-clamp technique.

Patch-Clamp Electrophysiology

The Patch-clamping is a versatile electrophysiological tool for understanding ion channel behavior. Every cell expresses ion channels, but the most common cells to study with patch-clamp techniques include neurons, muscle fibers, cardiomyocytes, and oocytes overexpressing single ion channels. Learn about patch-clamp electrophysiology and ion channel basics here.

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Series Resistance Compensation

Series resistance is the sum of all resistances between the amplifier and the inside of the cell using the whole-cell recording method. Due to Ohms Law, the larger this resistance, the greater the difference between the command level and the measured values. This creates an error in actual voltage or current measurement potentially leading to inaccurate observations. To overcome this, the Molecular Devices amplifiers have built-in circuitry to improve the bandwidth of the recording by compensating the error introduced by the voltage or current drop across the series resistance.

Single Channel Recording

The patch-clamp technique involves a glass micropipette forming a tight gigaohm seal with the cell membrane. The micropipette contains a wire bathed in an electrolytic solution to conduct ions. To measure single ion channels, a “patch” of membrane is pulled away from the cell after forming a gigaohm seal. If a single ion channel is within the patch, currents can be measured. The Axopatch 200B, with extremely low-noise profile, is ideal for this application, maximizing signal for the smallest conductance ion channels.

Voltage Clamp Amplifier

In an experiment using the voltage-clamp method, the investigator controls the membrane voltage in a cell and measures the transmembrane current required to maintain that voltage. This voltage control is called a command voltage. To maintain this command voltage level, an amplifier must inject current. The current injected will be equal and opposite the current escaping through open ion channels, allowing the amplifier to measure the amount of current passing through open membrane bound ion channels.

Whole Cell Recording

The whole cell patch-clamp technique involves a glass micropipette forming a tight gigaohm (GΩ) seal with the cell membrane. This micropipette contains a wire bathed in an electrolytic solution to conduct ions. A patch of membrane is subsequently ruptured by mild suction so that the glass micropipette provides a low-resistance access to the whole cell, thereby allowing the investigator to control the transmembrane voltage and allowing the investigator to evaluate the sum of all currents through membrane bound ion channels.