2,4-DINITROPHENOL-UNCOUPLING EFFECT ON DELTA-PSI IN LIVING HEPATOCYTES DEPENDS ON REDUCING-EQUIVALENT SUPPLY

Mitochondrial uncouplers, such as 2,4 dinitrophenol (DNP), increase th e cellular respiration by decreasing mitochondrial membrane potential (Delta Psi). We show that this respiratory effect can be transient or even prevented in isolated liver cells depending on the exogenous subs trate used (dihydroxyacetone vs. octanoate or proline), Moreover the d ecrease in ATP/ADP ratio induced by DNP is partially restored by addit ion of octanoate or proline, By using rhodamine 123 (Rh123) monitored by flow cytometry in living hepatocytes, we were able to follow in tim e Delta Psi in such DNP-uncoupled cells incubated with various substra tes, The ability of this method to evaluate Delta Psi changes was asse ssed by using myxothiazol (3.6 mu M), an inhibitor of the b-c1 complex of the respiratory chain which decreased Delta Psi (65%), or oligomyc in (6 mu g/ml), an inhibitor of the F0F1-ATPase which increased it (50 %). Although DNP induced a dose-dependent decrease of Delta Psi, we fo und that octanoate or proline addition prevented such effect. We propo se that octanoate or proline may counteract the uncoupling effect of D NP by providing a high supply of reducing equivalents to the respirato ry chain. (C) 1998 Wiley-Liss, Inc.