Ion permeation through bilayer lipid membranes (BLMs) is a fundamental process governing the transport of ionic drugs across biological membranes. In this study, we experimentally demonstrated that water-soluble but hydrophobic anions (HS-BODIPY2–) can be accumulated inside giant unilamellar vesicles (GUVs) by utilizing concentration gradients of driving cations (X+). By varying the cation species (X+ = K+, Na+, CH3NH3+, (CH3)2NH2+, (CH3)3NH+, and (CH3)4N+), the accumulation of HS-BODIPY2– strongly depended on both the species and concentration of X+. Hydrophilic cations such as Na+ and K+ also acted as driving ions in neutral GUVs, likely through affinity with phosphate or carbonyl groups of phospholipid headgroups. Furthermore, incorporation of cationic lipids enhanced the accumulation of HS-BODIPY2–, whereas anionic lipids had little effect. These findings demonstrate that ion-pair distribution into BLMs and cation-lipid interactions play crucial roles in governing membrane permeability of ionic species. The mechanism revealed here offers a novel and biocompatible strategy for controlling ion transport and encapsulating anionic drugs such as nucleic acids and nucleotides into liposomal systems.
Nakabayashi et al. (Thu,) studied this question.
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