Interactions of the fluorescent anion 1-anilino-8-naphthalene sulfonate with membrane charges in human red cell...

The interaction of the fluorescent anion 1-anilino-8-naphthalene sulfonate (ANS) with erythrocyte membranes was studied as a function of the charges in the membrane. The membrane charges were altered by including in the incubation medium the organic ions tetraphenylboron (TPB(-)), tetraphenylarsonium (TPA(+)) and tetraphenylphosphonium (TPP(+)) which differ in charge but have similar structure and high affinity for the membrane. TPB(-) decreases whereas TPA(+) and TPP(+) increase ANS fluorescence arising from the membrane. The fluorescence changes are accompanied by variations in the affinity and capacity of the membrane for ANS. The fluorescence arising under conditions where all the ANS present is within the membrane (by extrapolation to infinite membrane concentration) does not vary with these ions. Salicylate and SCN(-) which inhbit anion permeability also decrease ANS fluorescence with no apparent change in quantum yield. These results indicate that ANS exists as an anion in the membrane, associated with the regions involved in ion permeability, and that the concentration of ANS in the membrane is a function of the concentration of all the ions present in the medium and their relative affinities for the membrane. Thus, variations in ANS fluorescence reflect redistributions of the ANS ions following changes in electrostatic interactions with the membrane fixed charges.