DiO-C3-(5) and DiS-C3-(5): Interactions with RBC, ghosts and phospholipid vesicles.

The experiments presented below compare the interaction of diO-C3-(5) and diS-C3-(5) with erythrocytes, erythrocyte ghosts and phospholipid vesicles derived from erythrocyte membranes. The results confirm earlier reports of diS-C3-(5) dimerization in the presence of hemoglobin and of dye aggregate formation in erythrocyte suspensions. DiO-C3-(5), on the other hand, binds to vesicles and ghosts freed of hemoglobin in a potential-dependent manner but without forming dye aggregates. The two dyes bind to the different preparations in similar proportions, but diS-C3-(5) is bound in amounts 3-40 times greater depending on the degree of polarization. The results show that mechanism other than binding to hemoglobin must occur in order to explain the potential-dependent binding of both dyes to ghosts and vesicles. A primary interaction must exist between the dye molecule and the lipid bilayer in a biological membrane, and this would be expected to occur in the presence of hemoglobin or other cytosolic components. DiO-C3-(5) is a better dye to use than diS-C3-(5) for mechanistic studies, in order to avoid problems associated with formation of complex aggregates of the latter dye, especially in hyperpolarized membrane suspensions.