[Mechanism of the fluorescent response of carbocyanine probe diS-C3-(5) to membrane potential change].

A method for estimation of constants of carbocyanine probe diS-C3-(5) partition between water and membrane phases was developed based on the analysis of fluorometric titration curves. The partition constants (K) of this dye were calculated (the ratio of dye mole fraction in membrane and water phases) for sarcoplasmic reticulum (SR) vesicles in sucrose K = (1.15 +/- 0.04) X 10(7) and salt K = (6.12 +/- 0.07) X 10(6) media and for the asolectine liposomes in salt medium K = (3.4 +/- 0.2) X 10(7). The probe partition between water and lipid phases was calculated for different membrane concentrations. Critical aggregation concentrations of probe in lipid phase were estimated to be approximately 8 mol. probe per 1000 mol. lipid for asolectine liposomes and approximately 9 mol. per 1000 mol. lipid for SR vesicles (both in salt medium), approximately 6 mol. per 1000 mol. lipid for SR vesicles in sucrose medium. On the basis of own and literature data a mechanism of voltage-sensitive probe response related to probe aggregation in membranes was suggested.