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Although nanoplastics have well-known toxic effects toward the environment and living organisms, their molecular toxicity mechanisms, including the nature of nanoparticle–cell membrane interactions, are still under investigation. Here, we employ dynamic light scattering, quartz crystal microbalance with dissipation monitoring, and electrophysiology to investigate the interaction between polystyrene nanoparticles (PS NPs) and phospholipid membranes. Our results show that PS NPs adsorb onto lipid bilayers creating soft inhomogeneous films that include disordered defects. PS NPs form an integral part of the generated channels so that the surface functionalization and charge of the NP determine the pore conductive properties. The large difference in size between the NP diameter and the lipid bilayer thickness (∼60 vs ∼5 nm) suggests a particular and complex lipid–NP assembly that is able to maintain overall membrane integrity. In view of this, we suggest that NP-induced toxicity in cells could operate in more subtle ways than membrane disintegration, such as inducing lipid reorganization and transmembrane ionic fluxes that disrupt the membrane potential., This study was funded by the Spanish Government MCIN/AEI/10.13039/501100011033 (project 2019-108434GB-I00 to A.A. and project IJC2018-035283-I to M.Q.-M.), Universitat Jaume I (project UJI-B2018-53 to A.A. and UJI-A2020-21 to M.Q.-M and D.A.P.), Generalitat Valenciana (project GRISOLIAP/2018/061 to D.A.P. and A.A., project AICO/2020/066 to A.A., and grant BEFPI/2020/040 to D.A.P.), the Swedish Research Council (grant numbers 2016-05157 and 2021-05498 to M.M.), the Independent Research Fund Denmark (grant number 9040-00020B to M.M. and E.P.-O.), and the LEO Foundation Center for Cutaneous Drug Delivery (grant number 2016-11-01 to M.M.).

Adsorption processes are central to ionic transport in industrial and biological membrane systems. Multivalent cations modulate the conductive properties of nanofluidic devices through interactions with charged surfaces that depend principally on the ion charge number. Considering that ion channels are specialized valves that demand a sharp specificity in ion discrimination, we investigate the adsorption dynamics of trace amounts of different salts of trivalent cations in biological nanopores. We consider here OmpF from Escherichia coli, an archetypical protein nanopore, to probe the specificity of biological nanopores to multivalent cations. We systematically compare the effect of three trivalent electrolytes on OmpF current–voltage relationships and characterize the degree of rectification induced by each ion. We also analyze the open channel current noise to determine the existence of equilibrium/non-equilibrium mechanisms of ion adsorption and evaluate the extent of charge inversion through selectivity measurements. We show that the interaction of trivalent electrolytes with biological nanopores occurs via ion-specific adsorption yielding differential modulation of ion conduction and selectivity inversion. We also demonstrate the existence of non-equilibrium fluctuations likely related to ion-dependent trapping–detrapping processes. Our study provides fundamental information relevant to different biological and electrochemical systems where transport phenomena involve ion adsorption in charged surfaces under nanoscale confinement.

Trabajo presentado en el BPS2022: 66th Biophysical Society Annual Meeting, celebrado en San Francisco, California (Estados Unidos), del 19 al 23 de febrero de 2022., Polystyrene nanoparticles can be chemically synthetized at will or naturally produced by environmental degradation of polystyrene, being considered contaminants in the latter case. Their well-known capacity to induce several ecoand toxicological effects by both in vivo and in vitro studies occurs via cellular uptake and interaction with cell membranes, among others. Considering that the dimensions of most nanoparticles exceed considerably the typical bilayer thickness, the molecular details of nanoparticle-membrane interactions are captivating but still poorly understood. Our study focuses on the interaction of polystyrene nanoparticles with biologically relevant PC:PE:PS (5:3:2) lipid membranes under physiological conditions using quartz crystal microbalance with dissipation monitoring (QCM-D) and planar membrane electrophysiology (PME). Nanoparticles without functionalization (PS) and the functionalized cationic unsaturated amino (PS-NH2) and anionic carboxylated (PS-COOH) with same diameter (¿60 nm) have been tested. QCM-D experiments show that the three types of nanoparticles effectively reach the membrane surface, although in different fashions. Higher and faster depositions were found for PS-NH2 nanoparticles, while PS nanoparticles were found to interact very little with supported lipid membrane. PME recordings show bilayer permeabilization in a similar way than that induced by membrane proteins. Nanoparticleinduced currents show random transitions between different conductive levels of diverse lifetime rather than a progressive disintegration of the membrane. PS-COOH nanoparticles seem to be the least membrane-disruptive, while PS-NH2 nanoparticles turn to have the greatest disruption capacity. Selectivity experiments show currents whose preference for anions or cations is determined by the nanoparticle charge, demonstrating that nanoparticles are an integral part of the generated pores. Overall, our experiments show that nanoparticles do not induce membrane disintegration but probably compromise cell homeostasis in more subtle ways similar to protein ion-channels, suggesting a possible scenario for nanoparticle-induced toxicity.

Micro- (, This work was financed by Generalitat Valenciana (GV-2014/085-Prometeo-II), and talian Antarctic Research Program (PNRA) contract number: PNRA 16_0075 NANOPANTA: Nano-Polymers in the Antarctic marine environment and biota

The outer membrane of Gram-negative bacteria contains &beta, barrel proteins that form high-conducting ion channels providing a path for hydrophilic molecules, including antibiotics. Traditionally, these proteins have been considered to exist only in an open state so that regulation of outer membrane permeability was accomplished via protein expression. However, electrophysiological recordings show that &beta, barrel channels respond to transmembrane voltages by characteristically switching from a high-conducting, open state, to a so-called &lsquo, closed&rsquo, state, with reduced permeability and possibly exclusion of large metabolites. Here, we use the bacterial porin OmpF from E. coli as a model system to gain insight on the control of outer membrane permeability by bacterial porins through the modulation of their open state. Using planar bilayer electrophysiology, we perform an extensive study of the role of membrane lipids in the OmpF channel closure by voltage. We pay attention not only to the effects of charges in the hydrophilic lipid heads but also to the contribution of the hydrophobic tails in the lipid-protein interactions. Our results show that gating kinetics is governed by lipid characteristics so that each stage of a sequential closure is different from the previous one, probably because of intra- or intermonomeric rearrangements.