Method for kinetic study of in vitro conversion of a C14-labeled substrate to CO2

Abstract

A method is described for the determination of CO2 and C14O2 production rates by tissue slices incubated in the presence of a constant concentration and constant specific activity of a C14-labeled substrate. The constant conditions were maintained by periodic replacement of the incubation medium and gas phase. It is pointed out that, in order to determine the true rates of conversion to CO2 of an exogenous labeled substrate and of an endogenous, nonequilibrating CO2 precursor, measurements must be made after isotopic equilibration is attained. In the case of whole brain slices, such equilibration was observed after 3–4 hours of incubation. With glucose as the exogenous substrate, 30–40% of the CO2 produced by rat whole cerebrum slices was derived from endogenous sources for as long as 12 hours. Submitted on December 14, 1959