Measure hydrostatic pressure in small vessels and oocytes
Utilizes a liquid filled micropipette (2–5 µm tip opening) for sensing pressure
Pressure range from 1–100 mmHg (pressure range to 350 mmHg is available)
Lower limit 1 mmHg (133 Pa)
Includes calibration/test chamber
Tubing and fittings for interconnecting system sub-components are provided
Pressure in the pipette can be manually set to positive or negative relative to the outside
Probe holder for mounting on micromanipulator is included
10 pre-pulled pipettes are included
Measures biological pressures in very small liquid (aqueous) filled spaces
Pre-configured pipettes are available for convenience
Pressure in kidney tubules
Embryonic blood pressure
Mouse intraocular pressure
The 900A system is designed to measure liquid pressures dynamically in aqueous biological micro-environments, such as in kidney tubules or intracellular pressures. A liquid filled micropipette is used as a pressure probe, and pressure external to the pipette is measured at the tip. The outside diameter of the micropipette tip typically measures between 2–7μm. Pressure measurement is achieved by monitoring the pipette’s electrical resistance. The resistance changes according to changes in the pressure outside the pipette tip via displacement of an electrolyte concentration gradient. As the position of the concentration gradient changes, the resistance of the pipette changes. The resistance signal from the pipette is used as feedback to control a pressure source that applies pressure to the inside of the pipette to counterbalance pressure from the outside. The feedback loop forces the gradient to a neutral balance point, which is user-defined at atmospheric pressure beforehand. The internal pressure required to equally balance the external pressure to the neutral point is readily measured, and it is converted into an analog voltage available at the pressure output BNC and displayed numerically on the LED meter.
The 900A requires stable sources of both pressure and vacuum, which are essential for the system to rapidly counteract changing pressures encountered at the pipette tip. Pressure and vacuum sources are not provided with the 900A instrument because some labs are already equipped with suitable sources of pressure and vacuum. For researchers who do not possess pressure or vacuum sources, a cylinder of compressed air or inert gas with a dual stage regulator serves very well as a pressure source. Vacuum must be very stable. It is often best supplied by a quality vacuum pump. WPI offers a very quiet continuous duty vacuum pump well suited for use with the system. In addition, a vacuum regulation kit is recommended to fine tune the vacuum source to the ideal level (900A-VAC).
A manometer or meter for independent pressure measurement is necessary to calibrate the pressure and vacuum sources, as well as for validation of the performance of the 900A system prior to experimental use. A pressure measurement device capable of measuring within a range of +300 mmHg and –150 mmHg is recommended (PM015D or PM015R). For system performance validation at pressures well below 100 mmHg, the PM01D or PM01R is recommended, because it provides higher resolution at low pressure.
For transient response performance evaluation, a rapid burst of air or water pressure is required. WPI’s PV830 or PV820 series PicoPumps provide this capability. Rapidly occurring transient pressure measurements are typically captured on a data acquisition system. For details about testing and measurement of rapidly occurring pressure phenomena, contact a WPI sales representative for additional information.
Measuring electric potential and pressure simultaneously lets you use potential recording as an additional cue for locating the electrode where visibility is limited, or correlate pressure and potential when this is meaningful. The unique “Set Pressure” mode lets you preset the internal pressure of the microelectrode - select a positive pressure for flushing the tip, or a negative pressure for pulling solution into the tip. By disconnecting the microelectrode holder and attaching the tubing to a manometer, you can check the calibration against a standard.
A built-in alarm sounds to indicate maximum pressure. The alarm also sounds when the tip is blocked or electrical continuity is broken (e.g., the microelectrode comes out of the solution, too little filling solution to cover the Ag/AgCl pellet, disconnected ground reference, etc.).
Piezoelectric pressure controller
The piezoelectric pressure controller regulates internal pipette pressure by controlling air flow into and out of a small pressure chamber. A vacuum source is connected on the outlet side of the chamber, and a piezoelectric valve meters air entering the pressurized chamber. The residual volume of the pressure chamber includes the micropipette, the connecting tubing and the pressure transducer on the outlet side of the piezoelectric valve. The 900A accurately controls and adjusts the pressure in the chamber to match pressures applied externally to the microelectrode tip. The response time of the piezoelectric valve is 0.5?ms from fully closed to fully open. Overall system response time depends largely on the amount of residual volume in the tubing. When this volume is small, the system responds very rapidly (typically 10 milliseconds).
Minimize dead space
The lightweight pressure controller pod may be mounted close to the microelectrode using small-bore tubing, to minimize system dead space. Note
Microelectrode holders MEH6RF and MEH6SF for 1.0mm O.D. capillary glass included. (1.2, 1.5 and 2.0mm also available - please specify when ordering.)