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Flux / Slope

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high-resolution terminology - matching measurements at high-resolution


Flux / Slope

Description

Flux / Slope is the pull-down menu in DatLab for (1) normalization of flux (chamber volume-specific flux, sample-specific flux or flow or flux control ratios), (2) flux baseline correction, (3) background correction, and (4) flux smoothing, selection of the scaling factor, and stoichiometric normalization using a stoichiometric coefficient.

For each channel, the signal for the measured substance X is typically calibrated as an amount of substance concentration, cX [µM = nmol/ml]. The signal of the potentiometric channel, however, is primarily expressed logarithmically as pX=-logcX and then transformed to cX. The slope is calculated as the change of concentration over time, dcX/dt [nmol/(s · ml)]. In a chemical reaction, the change of substance X is stoichiometrically related to the changes of all other substrates and products involved in the reaction. If the stoichiometry of the reaction is normalized for substance X, then its stoichiometric coefficient is unity and νX equals 1 if the substance is a product formed in the reaction, but νX equals -1 if the substance is a substrate consumed in the reaction. Oxygen is formed in photosynthesis and νX=1 when expressing photosynthesis as oxygen flux. Oxyygen is consumed in aerobic respiration and νX=-1 when expressing respiration as oxygen flux.

In an ideally closed chamber, the external fluxes are zero, thus that the concentration changes are exclusively due to (internal) transformations, which are chemical reactions. Then respiratory flux expressed per unit of chamber volume can be calculated from the slope of oxygen concentration over time as

 X Slope neg = dcX/dt · νX-1 · SF

For the oxygen channel, cO2 is the oxygen conentration [nmol/ml = µmol/l = µM], dcO2/dt is the (positive) slope of oxygen concentration over time [nmol/(s · ml)], νO2-1 = -1 is the stoichiometric coefficient for the reaction of oxygen consumption (oxygen is removed in the chemical reaction, thus the stoichiometric coefficient is negative, expressing oxygen flux as the negative slope), and SF=1,000 is the scaling factor (converting units for the amount of oxygen from nmol to pmol).


is the negative slope, (dc/dt) · ν-1,

JV is O2 flux per volume [pmol/(s·ml)] (or volume-specific O2 flux),

provides the option to display the plot and all values of the flux (or flow, or flux control ratio) as the total flux, J, minus a baseline flux, J0.

JV(bc) = JV - JV0
JV = (dc/dt) · ν-1 · SF - V

, and V is the volume-specific background oxygen flux (background correction).

Abbreviation: J


MitoPedia O2k and high-resolution respirometry: DatLab