In 2009 we published a method for measuring mitochondrial ADP-ATP exchange rate mediated by the adenine nucleotide translocase (ANT): Biophys J. 2009 Mar 18;96(6):2490-504.
The method can be applied not only in isolated mitochondria, but also permeabilized cells and tissue homogenates.
An improved calibration step of this method has been published in Methods Enzymol. 2014;542:333-48
This methodology is presented in details in http://antactivity.com