A Comparison of Ussing Chambers

Comparing Ussing Chambers

March 31, 2023 In Chambers & Sliders By A.I. Michelson

Ussing chambers are an essential tool in physiology research of epithelial transport and barrier function. It is a device used to quantitate the transport of ions and other molecules across epithelial tissues such as the intestine, lung, and kidney.

There are relatively few companies that manufacture Ussing chambers, with the most popular systems being made by Physiologic Instruments and Warner Instruments.This article will compare and contrast Ussing chambers made by these two companies. We conclude based on several key factors that, while both are good systems, the EasyMount system from the Physiologic chamber is the superior product compared to the Navicyte system made by Warner Instruments. Let’s first take a basic look at the two systems starting with the Navicyte system from Warner Instruments.

Navicyte Ussing Chamber made by Warner Instruments

Description:  The Ussing chamber made by Warner Instruments is a six-chamber system that is compact, and will fit in most spaces. This system is essentially the “Navicyte” system that was originally developed by Grass and Sweetana in 1988 and later sold to Harvard Bioscience of which Warner Instruments is a subsidiary. The system consists of an anodized aluminum base and back plates, an acrylic front plate and large wingnuts to clamp the chambers between the front and back plates. Water flowing through channels in the front and back plates provides for heating the chambers and air control valves are used to control stirring and oxygenation of the fluids in the chambers.The system accommodates up to 6 Ussing chambers. Chambers are machined acrylic and are designed with a fixed size aperture to hold a specific tissue. There appears to be about a dozen different chambers available for this system. A unique feature of the Navicyte system is that the chamber halves are held securely together using a steel snap ring on both front and back of the chamber. Electrodes are held in position by special caps screwed to the chamber top. The electrodes are a chlorided silver wire placed in a glass barrel with a porous ceramic fritt at the bottom. The barrel is filled with KCl and communicates electrically with the solution in the chamber via the ceramic fritt. Tissues are generally mounted by stretching over stainless steel pins, although users have made a modification to permit mounting biopsy specimens. Cell cultures grown on Corning Snapwell inserts are easily mounted in the chamber designed for cell cultures.

 

All instruments have their good and bad points. Below we give our opinions of the Warner Navicyte Ussing Chamber:

 

The Good: 

1. These chambers have been around for more than 30 years.
2. The system is compact.
3. The system looks serviceable and well made.
4. The system has been cited in many research publications.

The Bad: There are a number of features we find problematic with the design:

1. Chamber heating is not equal between chambers. The chambers are heated from both the metal heat block behind the chamber and from the heated acrylic block in front. The chambers are squeezed between the heat sources by tightening the screws at each end of the heating bar. While this seems to be an ideal method, in reality it doesn’t work well because the front heat block bows outwards when tightened at the ends. This results in the chambers at the end having better contact with the heat sources and, thus, higher temperatures than those in the middle.
2. The electrodes are made from silver wire repeatedly dipped in molten AgCl and inserted into a glass capillary tube. The electrode wires appear to be quite stable. However, the glass barrels are expensive, extremely fragile, and are often broken when performing an experiment. Moreover, the ceramic fritts that separate the KCl inside the glass barrel can vary in thickness. When too thick, the electrode has a very high resistance. Too thin and the saturated KCl inside the barrel can diffuse or leak from the tip into the physiological buffer in the chamber and significantly alter experimental results. This has been tested by placing several KCl-filled barrels in 1 ml of distilled water and subsequently measuring K using flame photometry.
3. The electrodes are all inserted through the top of the chamber along with the airlines for stirring the solutions in the chamber. As seen in the above picture with six chambers installed there is considerable congestion with  24 electrodes and 12 airlines emanating from the top of chambers that are positioned side by side. Moreover, in most of the Navicyte chambers the voltage sensing electrodes enter the chambers at an angle. This means that removing any one chamber to mount a tissue requires that the electrodes in chambers on either side must be removed. This is not only inconvenient, but exposes those electrodes to unnecessary manipulation with likely changes in electrode offset potential.
4. Setup and mounting tissues is a complex procedure. Firstly, the chamber must be removed to mount the tissue, thus causing the electrodes to be removed and chamber temperature to drop. Secondly, as stated above, the chambers are not independent in that one must perturb chambers and electrodes on each side when removing a chamber to mount tissue.Thirdly, the chambers must be taken apart and then reassembled after mounting tissue. While this is not a difficult procedure, it does require removing and reinstalling two snap rings and is time consuming.
5. One must purchase different chambers for different tissues. 
6. Electrode barrels are easily broken and are expensive; however, as a plus, they can be washed aggressively to remove any drug contaminants. We feel these barrels are too expensive to be considered disposable.

EasyMount Ussing Chamber made by Physiologic Instruments

The EasyMount Ussing chamber made by Physiologic Instruments is a modular system and can be purchased to hold  2, 4, 6, or 8 chambers. The stands are of high quality anodized aluminum with a separate station for each chamber. The chambers are held in a spring-loaded aluminum  “cradle” that holds the acrylic chambers tightly against the heated back plate so that there is less than 1 degree temperature variation amongst chambers. Electrodes are made from chlorided silver wire or from sintered Ag-AgCl and inserted into modified pipettes that plug in through the front of the chamber with electrode leads passing cleanly down and under the chamber stand. Airflow regulation is by valves mounted to the stand behind each chamber. This arrangement yields a somewhat less compact, but much more user friendly system.
One of the most significant advantages of this chamber is the way in which tissues are mounted on what the company calls a “slider” that is installed in the chamber simply by inserting it from the chamber front. This requires only removing the solution from the chamber, separating the chamber halves slightly and sliding the tissue into the chamber. This procedure can be accomplished in only 20-30 seconds in the EasyMount chamber compared to more than 5 minutes for a Navicyte chamber. Moreover, because there is no need to remove the electrodes, the system is only slightly perturbed. It appears the Physiologic Ussing chamber system is designed to reduce the time and effort required for experiments. 

The Good:

1. Temperature uniformity amongst chambers
2. Electrodes are sturdy. Electrode tips are easy to prepare or can be purchased pre-filled and ready to use.
3. Chambers are pressed together by turning a thumb screw on the side of the cradle. This enables the user to “feel” the pressure being applied to make a seal with the tissue thereby reducing “edge-damage”.
4. No need to remove electrodes from the chambers when mounting tissues.
5. Electrode tips, unlike the fragile glass barrel tips of the Navicyte system, are  agar or gel filled and are at a price point to be considered to be disposable.
6. Tissues and cell cultures are first mounted on a slider and then inserted into the chamber rather than having to take the whole chamber apart as with the Navicyte system. This means that the same chamber can be used for multiple tissue types rather than having to purchase a different chamber for each tissue.
7. Sliders are available for over 20 different tissues and cell culture inserts making this an extremely flexible and more cost effective Ussing system.
8. The top of the EasyMount chamber is much less congested than the Navicyte chamber making it much easier for pipetting operations or for incorporating electrodes such as for pH stat operations.

Superiority of the EasyMount Ussing Chamber by Physiologic Instruments

Despite the compactness and quality of the Ussing chambers made by Warner Instruments, we deem the EasyMount system from Physiologic Instruments to be superior in nearly every aspect. To begin, the design of the EasyMount Ussing chamber is optimized for experimental accuracy, reproducibility and ease of use. The positioning of the electrode tips within the chamber ensures uniform contact area for the electrodes, reducing potential variations in current density. The use of the “slider” technology for mounting and inserting tissues into the chambers reduces the likelihood of contamination or damage to the sample. This design ensures that experimental results are accurate and reproducible.

The versatility of the slider technology used in the EasyMount system cannot be overstated. It makes this system extremely flexible so that the same chamber can be used with a tissue such as newborn mouse trachea (P2308, area 0.008 cm2) or with adult rabbit intestine (P2315, 1.26 cm2 ), a nearly 160 fold range in tissue aperture area. The smallest aperture chamber for Navicyte appears to be the 3 mm round, low volume, area 0.07 cm2 while the largest is the 8 x 24 mm oblong with pins, area 1.78 cm2, a 25 fold range. It should be noted that a user modification has been implemented to enable the 8 x 24 mm Navicyte chamber to be used with endoscopic biopsy specimens (Munch, 2010), whereas Physiologic Instruments provides 4 different sliders for biopsy specimens.

Finally, the customer support provided by Physiologic Instruments is reported to be excellent. Physiologic Instruments primarily offers equipment only for epithelial transport and barrier function research which is designed and produced in their facility in Reno, NV. The company has two Ph.D. scientists on staff with many years of benchtop research to guide and support the customer. . The company provides excellent technical support via email, Zoom, phone, and on-site training. All aspects of the EasyMount system were designed by Physiologic Instruments.

Product support by Warner Instruments/Harvard Bioscience is reported to be generally favorable, but not like the personal, in-depth support provided by Physiologic Instruments. This is likely because the Warner Instruments has multiple different types of instruments and chambers to support with no person on staff having multiple years of direct experience doing Ussing chamber work. Also, the designs of Ussing chambers sold by Warner Instruments were purchased from other vendors and not produced by company engineers.

Cost Comparison

We requested quotations from both companies for equivalent 6 channel Ussing systems. Results provided were: 

Company	6-channel Chamber System	6-channel for Electrophysiology
Warner Instruments	$13,788	$51,149
Physiologic Instruments	$10, 190	$39,975

Research Examples

Both the Easymount and Navicyte Ussing systems have been extensively used in scientific research. Numerous studies have utilized this Ussing chamber to study various aspects of epithelial transport. As examples, in a new article about to be published (Billip et al., 2023), several groups combined data independently garnered using Physiologic Instruments Ussing chamber to evaluate regulation of secretion by chemosensory Tuft cells which is a hallmark of Type 2 immunity. Others have used these systems to study nutrient absorption ( He, et  al., 2013), regulation of gut microbiome (Yin et al, 2017,  Grover & Kashyap, 2014), and effects of cytokines in cystic fibrosis (Rehman et al. 2021 ). Another study by Wu et al. (2022) utilized the same Ussing chamber to study regulation of ion transport across placental epithelium. Ussing chambers have recently been used for an exciting new area of research; namely, measuring transport across blood-brain barrier. Oppong-Damoah et al., 2019 used BEND3 cells grown in culture to form a confluent monolayer and the Ussing chamber to evaluate a nanoparticle drug-delivery system for oxytocin designed to increase its brain bioavailability through active transport.

Conclusion

In conclusion, the Ussing chamber technique has provided reliable and reproducible data to aid in our understanding of transepithelial and transendothelial transport and is an essential tool in physiology research. While both Ussing chambers made by Warner Instruments and Physiologic Instruments have their advantages, the one made by Physiologic Instruments appears to be superior for almost all Ussing chamber applications. 

A primary factor that can’t be over emphasized when comparing these two systems is the exceptional ease of use of the EasyMount system compared to the Navicyte system. Tissues can be mounted in the EasyMount system without even touching the electrodes in about 30 seconds. Mounting in the Navicyte system requires approximately 5 minutes per tissue and requires removing and replacing all of the electrodes making this system much more tedious to operate.

Finally, unless an investigator is interested only in measuring fluxes of labeled compounds across an epithelium, an experimental Ussing system must include more than just the chamber system. These additional items include the voltage /current clamp devices and data acquisition software as well as equipment for other addon methodologies such as pH stat. Comparisons of these products will be the subject of future reviews.