Measurement of oxygen consumption by the spectrophotometric oxyhemoglobin method

Avoid Excessive Oxygen Levels in Experiments with Organisms, Tissues and Cells

O2 levels encountered in vivo in cells and tissues are almost always at least an order of magnitude less than atmospheric pO2 because of sensing, signalling and bioenergetic demand. Although deleterious reactions are minimized by protective mechanisms (residual toxic products scavenged and detoxified) ambient levels should be mimicked in experiments with whole organisms, their isolated organs, tissues or cells and also with cultures of cell lines. These are also important issues for microorganisms inhabiting low O2 niches within higher organisms and their cells. Here, we highlight the importance of optimization of micro-aerobic conditions for experimentation and the deleterious consequences of not doing so.

Micromeasurement of total and regional CO2 productions in the one-day-old chick embryo

A conductometric micromethod combined with image analysis system has been developed allowing to determine the CO2 production within 'two-dimensional' tissues, i.e., flat and thin cell layers or epithelial sheets. The preparation was mounted into an airtight chamber separated in two compartments by a thin silicone membrane permeable to gases. The lower compartment contained the nutritive medium and the preparation. The upper compartment and a conductivity measuring capillary connected in series were perfused with a solution of Ba(OH)2. The CO2 produced by the tissue precipitated as BaCO3 and the resulting decrease of electrical conductivity was linearly related to the total CO2 production. In addition, the pattern of CO2 production was directly observable as the BaCO3 crystals formed upon the silicone membrane over the regions which produced CO2. The spatial distribution of the crystals was quantified by video image processing and the regional CO2 production evaluated with a spatial resolution of 100 microns. This new microtechnique was originally developed to study the CO2 production in the early chick blastoderm which is a disc 1-5 cells thick. At the stage of young neurula the CO2 production was found to be 235 +/- 37 nmol.h-1 (mean +/- SD; n = 10) per blastoderm and large variations of local CO2 production were detected from one region to another (from 0.6 to 6.5 nmol.h-1.mm-2). These results indicate a high metabolic and functional differentiation of cells within the blastoderm. The possible applications and improvements of such a microtechnique are discussed.