Conductance Change in Phospholipid Bilayer Membrane by an Electroneutral Ionophore, Monensin

Abstract

Monensin is a polyether antibiotic ionophore and is considered an electroneutral Na/H antiporter. Its addition, however, increased the conductance of phospholipid bilayer membrane, and this increase was observed only when the medium contained Na+. Analysis of the current-voltage curve suggested that the increase was due to the formation and the translocation of an univalently charged species. The conductance at zero external voltage was proportional to the second power of monensin concentration and increased with the decrease in pH of the medium. Modified monensin whose terminal carboxyl was esterified showed much larger increase (ca. 100 times) in conductance than intact monensin. We concluded that the complex between the dimer of protonated monensin and Na+ contributed to the electrogenic transport of monensin. This complex bears a +1 charge, which is consistent with the analysis of current-voltage curves. Contrary to the conductance, the Na+ transfer rate of liposomal membrane measured with 23Na-NMR was proportional to the monensin concentration, meaning that the electrogenic component contributes little to the total monensin-mediated Na+ transport in the present system. It should be noted that this electrogenic component may change the membrane potential.

Rhesus Rhadinovirus Infection of Rhesus Fibroblasts Occurs through Clathrin-Mediated Endocytosis

“…Bafilomycin A1 is a potent and specific inhibitor of vacuolar H ϩ ATPase, and it specifically inhibits endosomal acidification (6). Monensin, a sodium ionophore, binds monovalent cations, leading to an increase in endosomal pH (16). NH 4 Cl, an inhibitor of vacuolar acidification, is often used to examine pH sensitivity during virus entry (8).…”

Electrogenic and nonelectrogenic ion fluxes across lipid and mitochondrial membranes mediated by monensin and monensin ethyl ester

“…In contrast to the other popular polyether ionophore such as nigericin, monensin has a substantial preference for sodium over potassium ions as shown in the binding experiments [13,14] or in the transport experiments [15][16][17]. However, the experiments with planar lipid bilayers (BLM) [18,19] and liposomes [20,21] showed that monensin was able to transport sodium and potassium cations in an electrogenic manner, that is, generating electrical current on BLM and electrical potential on liposomes. The structural basis for this type of transport can be the structure of the acidic form of monensin with a sodium cation (I-COOH-M + ) present in crystal and in solutions, as has been proved by Huczyński et al [22].…”

“…One of the most commonly studied esters of monensin is its methyl ester (methyl-monensin), which was shown to elicit electrogenic sodium transport through liposomes better than the parental monensin [21]. This type of valinomycin-like action can be described in the scheme in Fig.…”

Structure, dynamics, and topological orientation of the polyether, ionophore antibiotic monensin, in a micellar environment

“…4 logical membranes, with a high affinity for sodium ions. Monensin disrupts the ion gradient created by The ion selectivity of monensin has been shown to depend on the C26-OH moiety.…”

“…The transport rate depends on the sodium concentration gradient across the membrane, Blocking the carboxyl group by chemical modification resulted in the complete loss of the ionophoric the pH of the environment, and of course, the concentration of monensin present in the membrane. [2][3][4] action. 5 Previous structural studies have shown that upon Ionophore polyether antibiotics such as monensin have the highest affinity for Na / but also have complexation with Na / , monensin adopts a pseudocyclic conformation in which the termini are the ability to bind and transport K / , Li / , Rb / , linked by head-to-tail hydrogen bonds, both in the Ag / , NH / 4 , amino acids, and ester salts under biocrystal form 3 and in a chloroform solution.…”