 Using WPI’s EVOM resistance meter, Endohm chambers provide reproducible resistance measurements of endo-thelial tissue in culture cups. Transfer cups from their culture wells to the Endohm chamber for measurement rather than using hand-held electrodes. The chamber and the cap each contain a pair of concentric electrodes: a voltage-sensing silver/silver chloride pellet in the center plus an annular current electrode. The height of the top electrode can be adjusted to fit cell culture cups of different manufacture. Endohm’s symmetrically apposing circular disc electrodes, situated above and beneath the membrane, allow a more uniform current density to flow across the membrane than with STX2 electrodes. The background resistance of a blank insert is reduced from 150Ω (when using WPI’s hand-held STX2 electrodes) to less than 5Ω. With Endohm’s fixed electrode geometry, variation of readings on a given sample is reduced from 10-30Ω with STX2 electrodes (depending on the experience of the user) to 1-2Ω . Compared with other resistance measurement methods, Endohm with EVOM offers a much more convenient and economic solution to leaky tissue measurement. Because of the uniform density of the AC square wave current from EVOM, errors owing to electrode polarization or membrane capacitance are largely eliminated. Endohm together with EVOM offers the most accurate and economical endothelial ohmmeter now available. To date, cups from Costar, Millipore, ICN Biomedicals, and Falcon have been tested. Endohm chambers may be sterilized with EtO, alcohol or a bactericide (also see: Cidex) not autoclavable.
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