Electrical Relaxation Experiments With Bilayer Lipid Membranes In The Presence Of Cationic Quinones

Mitochondria-targeted antioxidants consisting of a quinone part conjugated with a lipophilic cation via a hydrocarbon linker were previously shown to prevent oxidative damage to mitochondria in vitro and in vivo. In the present work, we studied the permeation of a series of compounds of this type across a planar bilayer phospholipid membrane. For this purpose, relaxation of the electrical current after a voltage jump was measured. All compounds studied exhibited slow relaxation kinetics in the time range from seconds to minutes. With respect to the characteristic time of the relaxation, hydrophobic cations can be ranked in the following series: 10(plastoquinonyl) decylrhodamine 19 (SkQR1) > 10-(6′-plastoquinonyl) decyltriphenylphosphonium (SkQ1) > 10-(6′-methylplastoquinonyl) decyltriphenylphosphonium (SkQ3) > 10-(6′-ubiquinonyl) decyltriphenylphosphonium (MitoQ). The relaxation was strongly dependent on the redox state of the quinone part of the molecule being substantially suppressed in the reduced form. Surprisingly, the kinetics of relaxation of several compounds depended not only on the phospholipid composition of the bilayer but also on the pH of the bathing solution.