Simultaneous measurement of metabolic heat rate, CO2 production, and O2 consumption by microcalorimetry

This study describes methods and equipment for measurement of metabolic heat rates of cells and tissues under conditions that provide simultaneous determinations of the flux rates of both O2 and CO2. Isothermal measurement of metabolic heats are conducted in a sealed ampule. A trapping solution is employed to absorb metabolic CO2. Absorption of CO2 produces heat at a rate proportional to the rate of CO2 production. Under these conditions, O2 consumption by the tissue results in a decrease in the partial pressure of O2 within the sealed ampule. The decrease in pressure can be monitored with a pressure sensor and related to O2 consumption rates. The combined measurements of heat rates, CO2, and O2 fluxes provide important information on bioenergetic efficiency of cell metabolism. These data can also suggest possible shifts in metabolic pathways or substrate sources as cells develop, or are exposed to effectors, inhibitors, and environmental factors.