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Acoustic Packets on a Flatland: A new basis for biological signaling?

This study provides first evidence that packets of sound can propagate without dispersion (solitary waves) in 2D single molecule thin films of phospholipids. The resulting systematic reorientation and condensation of the molecules was observed optically via energy transfer. The study predicts that single bio-molecules, the “inhabitants” of the flatland, can literally “talk” via the continuous 2D interface.

While the 2D acoustic phenomenon exhibit striking similarities (solitary, biphasic with a threshold) to communication in nerves, if it can indeed form a new basis for biological signaling remains to be seen.

Acoustic pulse

An optically measured solitary wave (top) that suggests a propagating local transition in a hydrated lipid interface (bottom). Note the stunning similarity to the biphasic shape of Hodgkin and Huxley's action potential.

Physics of Signaling

The existence and propagation of acoustic pressure pulses on lipid monolayers at the air-water interface are directly observed by simple mechanical detection. The pulses are excited by small amounts of solvents added to the monolayer. Controlling the state of the lipid interface, we show that the pulses propagate at velocities c following the lateral compressibility κ. This is manifested by a pronounced minimum in c (∼0.3 m/s) within the transition regime. The role of interface density pulses in biology is discussed, in particular, in the context of communicating localized alterations in protein function (signaling) and nerve pulse propagation.

Pressure pulse


Synaptic transmission by acetylcholine 

The transmission of a nerve pulse from a presynaptic to a postsynaptic cell (e.g., nerve, muscle, secretory cell, etc.) is fundamental for many physiological functions. In a prominent class of synapses transmission relies on acetylcholine (ACh). At present, it is assumed that ACh is (1) released by a nerve pulse, (2) binds to a membrane protein and (3) is hydrolyzed (i.e. deactivated) by acetylcholinesterase (AChE).

There are reasons to doubt this model: First, AChE is one of the fastest enzymes in nature. As such it will rapidly reduce the amount of synaptic ACh that can bind to another protein. Second, hydrolysis of ACh generates acetic acid. The protons donated by the acid may directly excite the postsynaptic membrane (as proposed by Konrad Kaufmann (Kaufmann 1977a, b, 1980)). We try to address the fundamental problem: Is a postsynaptic cell excited by intact ACh or by one of its hydrolysis products: the proton.  
ACh-synapse 


References:

• Kaufmann K. Acetylcholinesterase und die physikalischen Grundlagen der Nervenerregung (1980)
• Kaufmann K. Int. J. Quant. Chem. Supp. (1977) XII:169.

• Kaufmann K., Silman I. Naturwissenschaften (1980) 67:608.
• Fillafer C., Schneider M.F. Protoplasma (2015)

 


The dynamic, reversible clot

High shear induces aggregates that are only stable under flow. Once hydrodynamic stress is released they fall apart and are ready to be used somewhere else again.

Blood clot