Biomimetic Metal‐Sorbing Vesicles: Cd²+ Uptake by Phosphatidylcholine Vesicles Doped with Ionophore A23187

Abstract

Unilamellar phosphatidylcholine vesicles, harboring the ionophore, A23187, in the bilayer and the water-soluble chelating agent, nitrilotriacetate, in the vesicle interior, rapidly sequester and concentrate Cd2+ from dilute aqueous solution. Metal-sorbing vesicle permeabilities for cadmium ion at 5 ppm (42.8 microM) ranged from 8.09 x 10(-7) to 1.27 x 10(-4) cm/s for surface A23187 concentrations of 0.22-2.27 pmol/cm2 (which correspond to lipid:carrier molar ratios of 2000:1 to 200:1) and pH's from 5.5 to 8.5. The Cd2+ permeability shows linear variation with carrier concentration under the conditions studied. As pH is decreased, an increasing fraction of the A23187 becomes protonated, and the permeability exhibits a positive linear relationship with a function related to that for the fraction of unprotonated carrier. These noncovalently assembled, metal-sorbing vesicles exhibit shelf lives of several months and remain stable throughout typical metal sorption studies.

Ca2+ transport properties of ionophores A23187, ionomycin, and 4-BrA23187 in a well defined model system

“…In view of the above problems we have sought to develop a flexible and defined model system for investigating transport. The present system is an improvement over earlier vesicle-based systems (e.g., Pohl et al, 1980;Weissman et al, 1980;Blau et al, 1984;Smaal et al, 1985;Utsumi et al, 1985;Shastri et al, 1987;Blau and Weissman, 1988;Sokolove and Kestner, 1989;van Zanten et al, 1992;Walsh and Monbouquetle, 1993) in several ways. Preparation of loaded vesicles by freeze-thaw extrusion is straightforward and results in vesicles that are unilamellar, of relatively uni- a) -valinomycin 0.242 + 0.0005 25.2 + 0.3 b) + valinomycin 0.230 + 0.007 27.0 + 0.3 lonomycin a) -valinomycin 0.354 ± 0.011 31.6 ± 0.3 b) + valinomycin 0.398 + 0.002 32.4 + 0.2 4-BrA23187 a) -valinomycin 0.244 + 0.009 21.9 + 0.6 b) + valinomycin 0.260 + 0.008 27.5 + 0.6 All values are means + the SD (n = 5) obtained from experiments like those shown in Fig.…”

Vesicle Size Distributions Measured by Flow Field-Flow Fractionation Coupled with Multiangle Light Scattering

“…Unilamellar surfactant vesicles have long served as models for cell membranes (Johnson and Bangham, 1969) and more recently have been used as nanoscale vehicles for reagents in a wide variety of technologies, including drug delivery and targeting (Poste, 1980), medical imaging (Mauk and Gamble, 1979), nanocrystal formation (Korgel and Monbouquette, 1996;Fendler, 1987;Mann et al, 1986), separations (van Zanten and Monbouquette, 1992;van Zanten et al, 1995;Walsh and Monbouquette, 1993), and diagnostics (Jones et al, 1996). Vesicle size and size distribution are key parameters in most vesicle applications.…”

“…When used as reaction compartments for the synthesis of size-quantized nanocrystals whose optoelectronic properties are size-dependent, the vesicle size distribution must be as tight as possible, since it in turn governs the particle size distribution (Korgel and Monbouquette, 1996). Accurate estimation of ionophore-or ion channel-mediated ion permeability of vesicles also requires quantitative knowledge of the vesicle size and size distribution to calculate ion fluxes and permeabilities based on surface area (van Zanten and Monbouquette, 1992). Obviously, a strong need exists for rapid, dependable techniques to measure vesicle size and size distribution.…”

Electrochemical Measurements on Supported Phospholipid Bilayers: Preparation, Properties and Ion Transport Using Incorporated Ionophores

“…A23187 has also been described as a cadmium ionophore [32,33] and several stability constants have been determined for its 1 : 1 complexes with Ni 2þ , Fe 2þ , Zn 2þ and some other ions [33,34]. Two purified phospholipids, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE), were used for the formation of the lipid bilayer on a polycarbonate membrane support, which has been described as a simple and versatile approach [35].…”