Simultaneous measurement of metabolic heat rate, CO 2 production, and O 2 consumption by microcalorimetry

Abstract

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 O 2 and CO 2. Isothermal measurement of metabolic heats are conducted in a sealed ampule. A trapping solution is employed to absorb metabolic CO 2. Absorption of CO 2 produces heat at a rate proportional to the rate of CO 2 production. Under these conditions, O 2 consumption by the tissue results in a decrease in the partial pressure of O 2 within the sealed ampule. The decrease in pressure can be monitored with a pressure sensor and related to O 2 consumption rates. The combined measurements of heat rates, CO 2, and O 2 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.