Fluorescence of nicotinamide adenine dinucleotides during the active transport of Ca²⁺ ions in liver mitochondria

Abstract

Accumulation of Ca²⁺ ions by rat liver mitochondria increases the fluorescence of the reduced pyridine nucleotides in the presence of rotenone. The fluorescence increase is sensitive to the uncouplers of the oxidative phosphorylation and to the inhibitors of the electron transfer, providing the release of the accumulated Ca²⁺ from mitochondria. The substantial change of the fluorescence occurs in the presence of acetate, when the accumulated Ca²⁺ is present in the intramitochondrial space as soluble salt. Addition of Ca²⁺ to water solution of NADH and NADPH is followed by the slight increase of the fluorescence, while the same nucleotides dissolved in the more hydrophobic medium (methanol) considerably increase the fluorescence level by addition of Ca²⁺. The increase of the fluorescence of NAD(P)H in the mitochondria due to the accumulation of Ca²⁺ is considered not to be caused by the alkalinization of the intramitochondrial space but by the formation of the nucleotide-metal complex, localized at least partly at a hydrophobic phase.