Cation permeability induced by two 15-O5 macrocyclic polyether carriers in phospholipidic large unilamellar vesicles

Permeability of cryptands through dihexadecyl phosphate bilayer membranes

The leakage of Ru(bpy)3(2+) across a membrane of dihexadecyl phosphate (DHP) vesicles was compared when induced by (2.1.1), (2.2.1), (2.2.2.), (2.2.1.)C10 and (2.2.2.)C10-cryptands, and by (2.2.) and (2.2.)-bishydroxyethyl, i.e., ionizable macrobicyclic and monocyclic amino polyethers. Ru(bpy)3(2+) leakage increased as the permeant concentrations rose and was much higher for the very lipophilic cryptands. It also increased as the pH fell, and was lower and less dependent on the permeant concentration when induced by addition of partially titrated than by non-pretitrated cryptand. The efficiency of the permeant decreased as the alkali cation concentration rose and was independent of the cation type. It also varied with the membrane type: the efficiency of the (2.2.2.)C10-cryptand was higher on permeation of the membrane of DHP vesicles made from dihexadecyl phosphate than that of large unilamellar vesicles (LUV) composed of alpha-phosphatidylcholine, alpha-phosphatidic acid and cholesterol in an 8:1:1 molar ratio. The results are discussed in terms of the structural, physico-chemical and electrical characteristics of the permeating agents and of the membranes.

Pr3+ transport across phosphatidylcholine vesicles mediated by open crown synthetic ionophores

Pr3+ transport experiments, varying temperature and concentration, show that open crown synthetic polyethers (podands) mediate Pr3+ translocation across phosphatidylcholine vesicles by a carrier mechanism. Enhancement of the proton countertransport induced by addition of a protonophore, increases the cation inward rate.

Transport of alkali cations through thin lipid membranes by (222)C10-cryptand, an ionizable mobile carrier

The kinetics of K+ and Na+ transport across the membrane of large unilamellar vesicles (L.U.V.) were compared at two pH's, with two carriers: (222)C10-cryptand (diaza-1,10-decyl-5-hexaoxa-4,7,13,16,21,24-bicyclo[8.8.8.]+ ++hexacosane) and valinomcyin, i.e. an ionizable macrobicyclic amino polyether and a neutral macrocyclic antibiotic. The rate of cation transport by (222)C10 saturated as cation and carrier concentrations rose. The apparent affinity of (222)C10 for K+ was higher and less pH dependent than that for Na+ but resembled the affinity of valinomycin for K+. The efficiency of (222)C10 transport of K+ decreased as the pH fell and the carrier concentration rose, and was about ten times lower than that of valinomycin. Noncompetitive K+/Na+ transport selectivity of (222)C10 decreased as pH, and cation and carrier concentrations rose, and was lower than that of valinomycin. Transport of alkali cations by (222)C10 and valinomycin was noncooperative. Reaction orders in cation n(S) and carrier m(M) varied with the type of cation and carrier and were almost independent of pH; n(S) and m(M) were not respectively dependent on carrier or cation concentrations. The apparent estimated constants for cation translocation by (222)C10 were higher in the presence of Na+ than of K+ due to higher carrier saturation by K+, and decreased as pH and carrier concentration increased. Equilibrium potential was independent of the nature of carrier and transported cation. Results are discussed in terms of the structural, physiocochemical and electrical characteristics of carriers and complexes.