| Oocyte Clamping |
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Xenopus oocytes are commonly used as host cells for the study of ion channels, transport proteins, and other regulators of membrane conductance that are encoded by foreign mRNA that can express itself in these cells. Both cloned and acutely-isolated mRNA, can easily be injected into these large oocytes. These eggs can then produce most of the proteins that are encoded by the injected mRNA. Xenopus oocytes are useful for expressing ion channels because they have relatively few channel types of their own. This simplifies the measurement of ion currents from channels encoded by foreign mRNA. Channel currents can then be read with a modified two-electrode voltage clamp.
iWorx Features for Oocyte Clamping
Hardware
The iWorx 118 hardware can record at speeds of up to 100kHz with 16-bit data resolution. It connects to the computer via the USB port, so there are no cards to install. System noise is very low (<1mV) so even at low gains, A/D noise will never be a problem. The system offers two stimulator outputs and eight software-controlled digital outputs. The digital outputs of the iWorx 118 are BNC connectors on the front of the unit, so no special cables are required to connect the outputs to peripheral devices, such as the valve controller for the SF77 fast perfusion system.
LabScribe2 Software
Mode
LabScribe2 software can acquire data in either scope or chart mode (triggered snapshot or continuous mode) at speeds of up to 100,000 samples per second. In most oocyte applications, low speed recording in the chart mode is preferred.
Stimulator
The LabScribe2 software controls two independent stimulator outputs. Each output can be programmed separately, or combined to produce complex protocols. The stimulator supports a “Step” output especially designed for voltage clamping. The user specifies the number of steps to be taken from the starting voltage to the ending voltage, and the software does the rest. The stimulator can also be set to deliver a holding potential as the resting state for the output.
Digital Outputs
The eight digital outputs can be programmed easily using the LabScribe2 protocol generator. These outputs can be used to open or close perfusion valves, like those included in the Warner Instruments VC-6 Perfusion Valve Control System. These outputs can also be used to control the Warner Instruments SF-77B Fast Step Perfusion System.
Calibration
The Warner Instruments OC-725C Oocyte Clamp has a gain telegraph output that can be routed to one channel of the iWorx 118. LabScribe2 uses this signal to automatically calibrate your data in microamps, regardless of what gain you select on the clamp. The LabScribe2 software has gain telegraph options for all of the clamps and amplifiers made by Warner.
Time Annotations
While recording, you can mark your data with text messages.
These marks are searchable and appear in the field of data to which they apply. Marks are time locked to the record and can be used to “Go To” any marked region of the data. Marks are attached to the record by hitting the Return key or they can be delivered when an output line changes state. In this way, automated changes in perfusing solutions or drug deliveries can be marked for later review by the user.
System Components
iWorx 118 Eight-Channel Data Acquisition System
Receives the current and voltage values from the clamp, and controls clamp levels and the perfusion apparatus.
OC725C Warner Instruments Oocyte Clamp
Provides the head stages, bath clamp and voltage clamp amplifiers. For more information, visit Warner Instruments.
RC-3Z Oocyte Recording Chamber
The model RC-3Z features two slot-shaped bath wells; a narrow well for applications requiring rapid perfusion exchange and a wider well which permits good electrode access. Threaded holes are included for the attachment of a Warner oocyte clamp bath headstage.
MM33L Left Handed Micromanipulator for Current or Voltage Probe
MM33R Right Handed Micromanipulator for Current or Voltage Probe
MB/B Magnetic Base for MM33 Micromanipulators (two required)
The MM33 micromanipulators with magnetic mounts are accurate to 10 microns, adequate for managing oocyte injection and impalement.
Optional:
VC-6 Perfusion Valve Control System
Solenoid valve-controlled, gravity-driven perfusion system. For complete information, view the spec sheet at Warneronline.
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The IX-228S Recorder has 10 input channels and both a low voltage and a high voltage stimulator output. This recorder exhibits the high resolution and low noise required for small animal cardiovascular research, Oocyte clamp and high end metabolic research applications.