Probing electrophysiological activity of amphiphilic Dynorphin A in planar neutral membranes reveals both ion channel-like activity and neuropeptide translocation.

Dynorphin A (DynA) is an endogenous neuropeptide that besides acting as a ligand of the κ-opioid receptor, presents some non-opioid pathophysiological properties associated to its ability to induce cell permeability similarly to cell-penetrating peptides (CPPs). Here, we use electrophysiology experiments to show that amphiphilic DynA generates aqueous pores in neutral membranes similar to those reported previously in charged membranes, but we also find other events thermodynamically incompatible with voltage-driven ion channel activity (i.e. non-zero currents with no applied voltage in symmetric salt conditions, reversal potentials that exceed the theoretical limit for a given salt concentration gradient). By comparison with current traces generated by other amphiphilic molecule known to spontaneously cross membranes, we hypothesize that DynA could directly translocate across neutral bilayers, a feature never observed in charged membranes following the same electrophysiological protocol. Our findings suggest that DynA interaction with the cellular membrane is modulated by the lipid charge distribution, enabling either passive ionic transport via membrane remodeling and pore formation or by peptide direct internalization independent of cellular transduction pathways.

Biphasic concentration patterns in ionic transport under nanoconfinement revealed in steady-state and time-dependent properties.

Ion permeation across nanoscopic structures differs considerably from microfluidics because of strong steric constraints, transformed solvent properties, and charge-regulation effects revealed mostly in diluted solutions. However, little is known about nanofluidics in moderately concentrated solutions, which are critically important for industrial applications and living systems. Here, we show that nanoconfinement triggers general biphasic concentration patterns in a myriad of ion transport properties by using two contrasting systems: a biological ion channel and a much larger synthetic nanopore. Our findings show a low-concentration regime ruled by classical Debye screening and another one where ion-ion correlations and enhanced ion-surface interactions contribute differently to each electrophysiological property. Thus, different quantities (e.g., conductance vs noise) measured under the same conditions may appear contradictory because they belong to different concentration regimes. In addition, non-linear effects that are barely visible in bulk conductivity only in extremely concentrated solutions become apparent in nanochannels around physiological conditions.