Interactions of voltage-sensing dyes with membranes. I. Steady-state permeability behaviors induced by cyanine dyes

The effects of a series of thiadicarbocyanine dyes, diSCn(5), in altering the electrical properties of lipid bilayer membranes have been studied as a function of the membrane's intrinsic surface-charge density, the aqueous ionic strength, and the length (n) of the hydrocarbon side chains on the dye. Zero-current conductances, transmembrane potentials, and conductance-voltage relationships induced by these dyes were measured. All dyes studied altered membrane permeability properties; however these alterations were much larger at lower (e.g. 10(-3) M) than at higher (e.g. 10(-1) M) ionic strengths. The data suggest that such perturbations would not be troublesome for most biological preparations in which these dyes have been studied. The mechanisms by which these dyes alter membrane permeabilities vary in going from short-chained to long-chained dyes, the former forming voltage-gated, ion-permeant pores and the latter acting predominantly as anion carriers (forming 2:1 dye-anion complexes). In the case of diSC3(5), the predominant mechanism of altering membrane permeabilities changes in going from neutral to negatively charged membranes and also depends upon aqueous ionic strength and dye concentration.