The interaction of 3,3',4',5-tetrachlorosalicylanilide with phosphatidylcholine bilayers

Effect of 3-phenylindole on lipophilic ion and carrier-mediated ion transport across bilayer lipid membranes

The physical effects of 3-phenylindole, an antimicrobial compound which interacts with phospholipids, on ion transport across phosphatidylcholine-cholesterol bilayers have been investigated using three lipophilic ions and one ion-carrier complex. It was found that 3-phenylindole increased membrane electrical conductance of positively charged membrane probes and decreased electrical conductance of negatively charged probes. The enhancement of conductance detected by nonactin-K+ complex and tetraphenylarsonium+ was several orders of magnitude, whereas the suppression of conductance due to tetraphenylborate- and dipicrylamine- was less than a factor of ten. Presence of 3-phenylindole in aqueous phase slightly decreased adsorption of tetraphenylborate- and dipicrylamine- at the membrane surface. From the voltage dependence of the steady-state conductance it was shown that 3-phenylindole induced kinetic limitation of membrane transport of potassium mediated by nonactin. No such limitation was found in the case of tetraphenylarsonium+ transport. These results are shown to be consistent with the present concept of ion diffusion in membranes and the assumption that 3-phenylindole decreases the electric potential in the membrane interior. The asymmetry of the effect of 3-phenylindole on the magnitude of conductance changes for positively and negatively charged membrane permeable ions is also discussed as a reflection of the discreteness of both the absorbed 3-phenylindole and lipid dipoles.

Comparison of the photodynamic action of Rose Bengal and tetrachlorosalicylanilide on isolated porcine erythrocyte membranes

The light-mediated effects of Rose Bengal and 3,3',4',5-tetrachlorosalicylanilide (T4CS) on porcine erythrocyte membranes have been investigated. Irradiation in the presence of Rose Bengal and oxygen causes extensive destruction of the unsaturated fatty acids of the erythrocyte membrane. This results in a decrease in the membrane flexibility as measured by a nitroxide spin probe. Irradiation in the presence of T4CS and oxygen had no measurable effect on the unsaturated fatty acids or on the membrane flexibility. Irradiation of erythrocyte membranes both in the presence of Rose Bengal and oxygen and of T4CS gave rise to polymerisation of the membrane proteins. This was evident by polyacrylamide gel electrophoresis and by freeze-fracture electron microscopy. Aggregation of membrane proteins could be observed with low levels of Rose Bengal and short irradiation times at which no loss of unsaturated fatty acids could be detected. Irradiation of the n-butanol-extracted apoprotein of porcine erythrocyte membranes both in the presence of Rose Bengal and of T4CS resulted in polymerisation of the protein as measured by gel electrophoresis and electron microscopy. The results obtained from the two photodynamic compounds are compared in terms of their different mechanisms of action on the membrane. The implications of the results in determining the molecular events leading to photohaemolysis are discussed.