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Matthias F. Schneider

University of Dortmund

Title: On the physical basis of communication in living systems in general and it's specificity arising from thermodynamics.

Abstract: The ubiquitous hydrated interface has to obey the 2nd Law. The enormous power of this approach and it's consequences for life were first pointed out by K. Kaufmann starting in the late 80ties when following Einstein's approach to thermodynamics. This work is strongly inspired by his work. From a thermodynamic state to (biological) function. With the 2nd Law one finds, that state and state changes not only regulate morphological transitions, interface conductivity and catalytic rates etc. (see K. Kaufmann), but also determine the propagation properties of interfacial waves. Importantly, this mind set is in strong contrast to the molecular/structural approach. On Nerve Pulse Propagation. We demonstrate that the waves observed can be driven into a non-linear regime, where excitation becomes specific, i.e. only occurs over a certain threshold of the stimulus. This threshold, the different physical realizations (mechanical, electrical, optical, chemical...) and the shape of the pulse show a striking similarity with the nervous impulse and clearly support the approach of Kaufmann and Heimburg. On a physical basis of communication in general. Finally we demonstrate that these pulses can modulate the activity of enzymes and hence integrate the corner stone of biochemistry into a physical approach. While one enzyme may "send" a pulse another acts as a "receiver". This is in striking contrast to all known biological communication models where diffusion is the key element in the transport process (e.g. Lefkowitz, Nobel lecture 2012). Specificity. The specificity here arises from physics/thermodynamics and NOT structural considerations. Transitions of all kinds e.g. phase transitions in lipid tails or protonation-transitions take place for a very unique combination of thermodynamic variables (corresponding to a line or even a point when the phase diagram is 2D) and are hence "specific" from the get go. Hence, specificity does NOT need to be introduced by structural compatibility of two or more molecules (ligand/receptor model), but arises naturally from thermodynamics. This is in the spirit of Einstein's approach. In conclusion: Excitation, Propagation and Fluctuations are all consequences of the 2nd Law (Kaufmann) and lead to the integration of localized functions (e.g. conductivity or catalysis) by physical principles.

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