Specific requirement for inorganic phosphate for induction of bilayer membrane conductance by the cationic uncoupler carbocyanine dye.

The trinucleous divalent cationic cyanine dye triS-C4(5) was shown to be an uncoupler of oxidative phosphorylation in mitochondria only in reaction medium containing inorganic phosphate (Pi). This dye also induced marked increase in the electrical conductance of a phospholipid bilayer membrane in bathing solution containing Pi, but not in solution containing Tris-HCl buffer without Pi. Time-dependent fluctuation of the electrical current across the bilayer membrane was observed in the presence of triS-C4(5) only in bathing solution containing Pi. This fluctuation could be due to perturbation of the bilayer membrane structure induced by the cooperative action of the cyanine dye and Pi, and this perturbation should be directly related to their effects in increasing membrane conductance and also causing uncoupling in mitochondria.