Chloride Transport in Porous Lipid Bilayer Membranes

Abstract

This paper describes dissipative C1-transport in "porous" lipid bilayer membranes, i.e., cholesterol-containing membranes exposed to 1-3 X 10 -7 M amphotericin B. PDC, (cm. s-), the diffusional permeability coefficient for C-, estimated from unidirectional 86Cl-fluxes at zero volume flow, varied linearly with the membrane conductance (Gm, -1' cm-2 ) when the contributions of unstirred layers to the resistance to tracer diffusion were relatively small with respect to the membranes; in 0.05 M NaCI, PDoI was 1.36 X 10-4 cm s -1 when Gm was 0.02 -1. cm-2. Net chloride fluxes were measured either in the presence of imposed concentration gradients or electrical potential differences. Under both sets of conditions: the values of PDCI computed from zero volume flow experiments described net chloride fluxes; the net chloride fluxes accounted for 90-95 % of the membrane current density; and, the chloride flux ratio conformed to the Ussing independence relationship. Thus, it is likely that C1-traversed aqueous pores in these anion-permselective membranes via a simple diffusion process. The zero current membrane potentials measured when the aqueous phases contained asymmetrical NaCl solutions could be expressed in terms of the Goldman-Hodgkin-Katz constant field equation, assuming that the PDN/PDC1 ratio was 0.05. In symmetrical salt solutions, the current-voltage properties of these membranes were linear; in asymmetrical NaCI solutions, the membranes exhibited electrical rectification consistent with constant-field theory. It seems likely that the space charge density in these porous membranes is sufficiently low that the potential gradient within the membranes is approximately linear; and, that the pores are not electrically neutral, presumably because the Debye length within the membrane phase approximates the membrane thickness.

Effects of the plant alkaloid sanguinarine on cation transport by human red blood cells and lipid bilayer membranes

“…While the nature of the sanguinarine-induced conductance pathway is unknown, it is well established that the polyene antibiotics are pore formers (Andreoli & Monahan, 1968;Holtz & Finkelstein, 1970;Cass et al, 1970;Andreoli & Watkins 1973;Andreoli, 1974;Holtz, 1974). This raises the possibility that sanguinarine also induces channels in bilayers.…”

The Structure and Function of Amphotericin B‐cholesterol Pores in Lipid Bilayer Membranes*

“…The results of these studiesG have been summarized in TABLE 9. In regard to the antibiotic, it is evident that pore formation requires 38 rather than 28 ring atoms and an unsaturated C-20-C-33 segment, but it does not depend on a dissociable amino or carboxyl group.…”

Study of Chloride Transport Across the Rabbit Cortical Collecting Tubule

“…Because chloride is the principal extracellular anion, it is quite likely that the collecting tubule may, in part, control extracellular fluid by regulating reabsorption of chloride. Although the characteristics of chloride transport across many natural epithelia (4-6) and artificial membranes (7) have been examined in some detail, very little information is available regarding the handling of chloride by the mammalian distal nephron. The exact role of endogenous mineralocorticoid in the maintenance of extracellular fluid volume has likewise been intensively examined but not positively delineated (8)(9)(10).…”