Rapid fluorometric assay for mitochondrial proton adenosine triphosphatase activity for assessment of viability of liver graft tissue.

We developed an improved determination method of mitochondrial proton adenosine triphosphatase (ATPase) activity in the liver. The activity was measured fluorometrically with a 3,3'-dipropylthiodicarbocyanine iodide (diS-C3(5)), which is excited at 625 nm and emits fluorescence at 670 nm. This dye transmits the electric potential across the inner mitochondrial membrane. The fluorescence intensity of diS-C3(5) with mitochondria (100 microliters, 4-16 mg/ml protein) in a 2 ml potassium buffer (pH 7.4) was regarded as a standard electric potential. After confirming the activity of the mitochondrial electron transport chain by succinic acid (9 mumol), we inhibited the chain by antimycin A (1.25 micrograms). Fluorescence intensity decreased by adenosine 5'-triphosphate (ATP) (2 mumol) and oligomycin (25 micrograms) inhibited this depression. The value of mitochondrial proton ATPase activity was calculated as a percentage of the fluorescence intensity change by ATP per the standard electric potential. The activity of mitochondrial proton ATPase in the normal fresh rat livers was 50.3 +/- 2.2%. Good correlation (r2 = 0.807) between two methods for mitochondrial proton ATPase activity, our newly developed method and a conventional colorimetric method, was obtained in the rat livers with various conditions. This method has advantages that the proton ATPase activity can be measured in intact mitochondria, and all procedures can be completed within 40 min. It is suitable for the determination of mitochondrial viability of liver graft in the hepatic resections and transplantations.