Аннотация:Usnic acid is one of specific lichen compounds, which are formed as a result of metabolism and aren't found in other organism groups. Among hundreds of secondary lichen metabolites usnic acid is the most studied. It has antiviral, antibiotic, analgesic, anti-tuberculosis and insecticidal activities. Previous studies have shown that usnic acid is a highly lipophilic compound possessing protonophoric properties. Various mechanisms of the antibacterial action of usnic acid, including its protonophoric action and the ability to inhibit RNA synthesis, are discussed in the literature. In the present work, we also investigated ionophoric properties of minocycline, another antimicrobial agent. Recently, our laboratory showed that protonophoric action of usnic acid depends on the presence of calcium ions in the system. This work is aimed on the study of the ability of usnic acid to transfer calcium ions through the lipid membranes. Calcium homeostasis is known to play an important role in the functioning of cells; it can regulate the permeability of cell membranes and also involves in cell responses to external triggers.