Evidence for a transition in the cortical membranes of Paramecium.

Ever since the pioneering studies in the 1960s and 70s, the importance of order transitions for cell membrane functions has remained a matter of debate. Recently, it has been proposed that the nonlinear stimulus-response curve of excitable cells, which manifests in all-or-none pulses (action potentials (AP)), is due to a transition in the cell membrane. Indeed, evidence for transitions has accumulated in plant cells and neurons, but studies with other excitable cells are expedient in order to show if this finding is of a general nature.

Reversible single cell trapping of to correlate swimming behavior and membrane state.

Single cell measurements with living specimen like, for example, the ciliated protozoan can be a challenging task. We present here a microfluidic trapping mechanism for measurements with these micro-organisms that can be used, e.g.

Optical studies of membrane state during action potential propagation.

One of the most striking phenomena in biology is the action potential (AP), a nonlinear pulse with threshold and amplitude saturation (all-or-none-behavior) that propagates along neurons and other cells. In the classical interpretation the AP is considered to be an electrical phenomenon - a regenerating current flowing in a "biological cable". In contrast, the thermodynamic interpretation has emphasized that conservation laws necessitate pulses and that pulses must manifest as transient changes of all observables of the system (electrical, mechanical, thermal, etc.

The living state: How cellular excitability is controlled by the thermodynamic state of the membrane.

The thermodynamic (TD) properties of biological membranes play a central role for living systems. It has been suggested, for instance, that nonlinear pulses such as action potentials (APs) can only exist if the membrane state is in vicinity of a TD transition. Herein, two membrane properties in living systems - excitability and velocity - are analyzed for a broad spectrum of conditions (temperature (T), 3D-pressure (p) and pH-dependence).

Collision of two action potentials in a single excitable cell.

Background: It is a common incident in nature, that two waves or pulses run into each other head-on. The outcome of such an event is of special interest, because it allows conclusions about the underlying physical nature of the pulses. The present experimental study dealt with the head-on meeting of two action potentials (AP) in a single excitable plant cell (Chara braunii internode).