J. Biol. Chem., Vol. 263, Issue 16, 7574-7580, Jun, 1988
Inhibition of the mitochondrial inner membrane anion channel by dicyclohexylcarbodiimide. Evidence for a specific transport pathway
AD Beavis and KD Garlid
Department of Pharmacology, Medical College of Ohio, Toledo 43699.
Electrophoretic uniport of anions through the inner mitochondrial membrane
can be activated by alkaline pH or by depleting the matrix of divalent
cations. It has also been suggested that, in the presence of valinomycin
and potassium, respiration can also activate anion uniport. We have
proposed that a single pathway is responsible for all three of these
transport processes (Garlid, K. D., and Beavis, A. D. (1986) Biochim.
Biophys. Acta 853, 187-204). We now present evidence that like the
"pH-dependent" pore the divalent cation-regulated pore and the
"respiration-induced" pore are blocked by N,N'-dicyclohexylcarbodiimide
(DCCD). Moreover, the kinetics of inhibition of the latter two pathways are
identical and exhibit a second order rate constant of 2.6 X 10(-3) (nmol
DCCD/mg)-1.min-1. DCCD inhibits the uniport of Cl-, phosphate, malate, and
other lipophobic anions completely, but it has no effect on the classical
electroneutral phosphate and dicarboxylate carriers. In Mg2+-depleted
mitochondria DCCD partially inhibits the transport of SCN- ; however, in
Mg2+-containing mitochondria and at low pH, no inhibition is observed.
Furthermore, in DCCD-treated mitochondria, even following depletion of
Mg2+, the transport of SCN- is independent of pH. These results lead us to
conclude that two pathways for anion uniport exist: a specific, regulated
pathway which can conduct a wide variety of anions and a nonregulated
pathway through the lipid bilayer which only conducts lipid-soluble ions.