Physics (Internal)

Thermodynamic Triggered Transitions, Transport and Traffic in Biology Blood Clotting, Membranes and Nerves

This event is part of the Biophysics/Condensed Matter Seminar Series.

Abstract:
Soft interfaces near transitions or critical states represent a physical control mechanism of biological processes. Examples are given:

Imagine you rinse your dishes and everything keeps sticking harder — a drama for your kitchen but essential for us to survive. During blood clotting it was found that an increasing shear rate triggers an increase in adhesion of blood platelets — a phenomenon in clear contradiction or counterintuitive to our daily experience. Using acoustic driven microfluidics we mimic our circulatory system and show that the protein von Willebrand factor goes through a reversible global stretched transition which represents its haemostatic inactive-active state. The counterintuitive picture resolves by realizing the shear dependence of the transition.

The conventional model of nerve-pulse propagation accounts only for the electrical aspect of the pulse, however, the mechanical, optic, chemical and especially thermal aspects are entirely neglected. All these properties change reversibly during the propagation and none of them are explained by the Hodgkin and Huxley model. I present an alternative thermodynamic view that the nerve pulse propagation is actually a 2D sound wave propagating in the membrane. Keeping the membrane state near a transition enables control.

Importantly the same arguments hold for thermodynamic driven traffic and ion transport across lipid bilayers. Membrane budding, fission as well as lipid-ion-channel formation (or more precisely fluctuations) can be triggered and controlled by the phase transition of the system.

In summary the physics or thermodynamics of 2D soft interfaces predicts and explains a variety of observations in biology without the introduction of a “clever” protein. It therefore reposes the question for the role of proteins for membrane function.