The connection between action potentials and compression waves in lipid membranes

Experimental observations in lipid monolayers at the air-water interface have demonstrated that compression waves travelling close to the lipid melting transition display unusual nonlinear properties. These properties offer a potential means of communication. Furthermore, these properties are strikingly similar to those of action potentials observed in excitable cells, and points at possible novel aspects of action potentials. We use analytical and numerical tools to investigate these nonlinear compression waves, focusing on the interconnections between the mechanical, electrical, and chemical aspects of the lipid membrane, embedded proteins, ions, and solvent[8, 9, 16].

Ion-induced volume transition in polyelectrolyte gels and its role in biology

Polyelectrolyte hydrogels are soft complex systems made of charged crosslinked macromolecules, solvent, and counter and co-ions. Many types of polyelectrolyte hydrogels demonstrate an abrupt volume transition in response to minute changes of external environmental stimuli, such as temperature, ionic composition, solvent quality, pH, and electric field. Similar phenomena are found abundantly in living systems, and are also widely used in various man made applications. In this project we attempt to shed light on several distinct biological processes such as: compaction of DNA molecules, release of secretory products, and changes in the hydraulic flow in the xylem of vascular plants, by developing a dynamic physicochemical framework that accounts for the interaction of charged polymers, solvent, and ions[10, 12, 14].

Surface deformation during cellular excitability

The excitation of many cells and tissues is associated with observable mechanical changes. In neurons, mechanical deformation of the cell surface is usually revealed as a swelling followed by a contraction, with amplitudes of ∼1–10 nm. We previously demonstrated that in large excitable plant cells the rigid external layer (cell wall) hinders the underlying deformation, and observed significant cellular deformation that co-propagates with the electrical signal with amplitudes of ∼1—100 m. These transient cellular deformations are captured by an elastic model of the cell surface, suggesting that elastic properties of the surface are crucial for the explication of the phenomena[5,6]. Starting from very simple mechanical models, we introduce empirically motivated terms to better understand the mechanoelectrical coupling, its effect on intracellular components, and the nonelectrical information propagating to neighboring cells. The resulting models are of relevance for the description of several biological processes in their native state as well as for the understanding of certain clinically significant pathologies (primarily neurological ones).

Active transport induces drag of intracellular fluid

Active transport within the cell cytoplasm includes steady trafficking of different organelles and vesicles actively transported by motor proteins using chemical energy. We previously showed that indirect hydrodynamic interaction (flow-induced drag) that exists between actively transported cargoes and soluble particles is sufficient to account for the most relevant experimental observations pertaining to the slow-component transport in axons, which plays an important role in cell development and maintenance[2]. Further work in this area will aim to connect fundamental hydrodynamic principles with emerging properties of cell development. For instance, the rate of axonal growth might be shown to depend on delicate features of the microtubules facilitating the transport and the organelle transport rate.