Steady-state measurements of respiration rate with an oxygen electrode.

An oxygen electrode was developed which measures steady-state respiration rates in a volume of 0.25 ml and at oxygen concentrations as low as 0.1 μm. The steady state was achieved by pumping air-equilibrated buffer into the respirometer at various rates. The method is most suitable for tissue slices.     

Estimation of fermentation biomass concentration by measuring oxygen uptake off-line with an oxygen electrode

Summary An indirect method for biomass determination was developed for aerobic cultivation in media containing solid substrates. This method involved off-line estimation of oxygen uptake with an oxygen electrode using a calibration factor and was applied to penicillin fermentation with Penicillium chrysogenum. The volumetric oxygen uptake rate was independent of the amount of sample sealed in the measuring cell. Storage of the sample for a period up to 2.5 h also had no influence on the rate of O₂ uptake. The specific O₂ uptake rate at 70 to 75 h fermentation time was used as the calibration factor to calculate the respiration-active part of the biomass. Specific penicillin V formation rates related to net dry weight, respiration-active biomass (X _A )and RNA content were compared. Only the penicillin V production rate related to X _A showed a similar behaviour as the penicillin V production rate related to RNA content. For this reason, it is assumed that X _A ,like RNA content, is more closely related to the metabolic state of the cells than the net dry weight. This method, therefore, provides a more suitable reference parameter for fermentation control than the generally used net dry weight.Offprint requests to: D. Siegmund     

Influence of chlorophyll concentrations on the reliability of measurements with an oxygen electrode when studying photosynthetic efficiency in bioassays using microalgae

Euglena gracilis and Chlamydomonas reinhardtii were used as model organisms to establish the best conditions for studying photosynthetic efficiency using the Light Pipette – experimental system, which enables sensitive detection of changes in oxygen evolution/consumption and an easy collection and digitalisation of data. Chlorophyll concentrations of 0.005, 0.025, 0.050 and 0.075 mgmL^-1 were investigated using different light regimes. Cultures of E. gracilis at the same chlorophyll concentration absorbed more light(measured at 580 μmol m^-2 s^-1) than those of C. reinhardtii. Cell density had a considerable effect on the reliability of measurements. Chlorophyll concentrations between 0.025 mg_Chl ml^-1 and 0.050 mg_Chlml^-1 can be recommended when applying the Light Pipette system in bioassays using microalgae. This revised version was published online in August 2006 with corrections to the Cover Date.     

Factors affecting the respiration of rabbit sperm measured with an oxygen electrode

The respiration of rabbit sperm was measured by a Clarke type electrode which has two advantages over the conventional Warburg technique, greater sensitivity, and no necessity for a carbon dioxide-free atmosphere. It was not necessary to resaturate the sample chamber of the oxygen monitor with air, down to about 30% desaturation.Rabbit seminal plasma had a measurable oxygen uptake (0.6 μl/hr/ml) but this was much less than for human seminal plasma (4.3 μl/hr/ml). Hoderate dilution of the sperm and storing the semen at 0°C after slow cooling had no effect on oxygen uptake. Unlike those of most other species, rabbit sperm were also little affected by deliberate exposure to cold shock and the respiration before and after rapid cooling to 0°C was about the same. On the other hand very brief exposure of rabbit sperm to 65°C abolished motility and greatly reduced the respiration rate. Bicarbonate (6 mM) stimulated the oxygen uptake of freshly collected samples of rabbit sperm after washing. Increasing the phosphate concentration of the medium to 80 mM did not greatly depress the oxygen uptake.     

Halothane interference at an amperometric oxygen electrode: the development of an oxygen/halothane sensor

The role of electrode materials in the reduction of halothane and oxygen mixtures at rotating and stationary electrodes is considered. Halothane is found to be electroactive within the available electrode-potential range on silver and on gold. Double potential step experiments are considered in order to isolate the individual halothane and oxygen signals. A double integration, single potential step technique is evaluated for the quantitative simultaneous measurements of oxygen and halothane on gold.The influence of electrode purity is discussed in terms of a reaction mechanism and electrode output error.     

Anticancer drug sensitivity testing using an oxygen electrode apparatus

Conventional anticancer drug sensitivity testing methods, such as succinate dehydrogenase inhibition (SDI), histoculture drug-response assay (HDRA) and collagen gel droplet embedded culture drug sensitivity testing (CD-DST), all require primary culturing and are extremely complex tests that require considerable time for analysis. A major drawback of these methods is that if culturing is not performed properly, ambiguous results are produced. Therefore, we developed an oxygen electrode apparatus that uses cellular metabolism as an indicator of anticancer drug sensitivity and investigated its usefulness in 29 breast cancer patients with the following histopathological classifications: papillotubular carcinoma (n= 15); solid tubular carcinoma (n= 6); and scirrhous carcinoma (n= 8). Comparison of anticancer drug sensitivity testing results obtained using the conventional HDRA method and those obtained using the oxygen electrode apparatus showed significant reproducibility between the two methods. In addition, similar anticancer drug sensitivity testing results using the oxygen electrode apparatus were obtained for in vivo testing of nude mice transplanted with established cancer cell lines. These findings suggest that the oxygen electrode apparatus is a useful procedure in anticancer drug sensitivity testing that provides better reproducibility and that is faster, more convenient, and less expensive than other testing methods.     

An on-line system for measuring photosynthetic characteristics via an oxygen electrode

In this note we describe a simple hardware-software combinationthat affords a rapid and accurate determination of the photosynthesis-lightirradiation (P versus I) relationship using an oxygen electrode.     

A system for measuring phytoplankton photosynthesis in a defined light field with an oxygen electrode

A system is described for the precise continuous measurementof oxygen consumption and photo-synthetic oxygen evolution ina well defined light field with a polarographic oxygen electrode.The procedure uses a parallel light beam to irradiate samples,a relatively short pathlength and temperature regulation. Maximalsensitivity of the O₂-mcasurement is 1.4 µmol O₂/mV at20°C. The O₂-chamber and the O₂-amplifier are presentedin full detail together with a typical recorder tracing of aphotosynthesis-irradiance curve.