title: Protons at the speed of sound: Predicting specific biological signaling from physics.
abstract: Local changes in pH are known to significantly alter the state and activity of proteins and enzymes. pH variations induced by pulses propagating along soft interfaces (e.g. membranes) would therefore constitute an important pillar towards a physical mechanism of biological signaling. Here we investigate the pH-induced physical perturbation of a lipid interface and the physicochemical nature of the subsequent acoustic propagation. Pulses are stimulated by local acidification and propagate - in analogy to sound - at velocities controlled by the interface's compressibility. With transient local pH changes of 0.6 directly observed at the interface and velocities up to 1.4 m/s this represents hitherto the fastest protonic communication observed. Furthermore simultaneously propagating mechanical and electrical changes in the lipid interface are detected, exposing the thermodynamic nature of these pulses. Finally, these pulses are excitable only beyond a threshold for protonation, determined by the pKa of the lipid head groups. This protonation-transition plus the existence of an enzymatic pH-optimum offer a physical basis for intra- and intercellular signaling via sound waves at interfaces, where not molecular structure and mechano-enyzmatic couplings, but interface thermodynamics and thermodynamic transitions are the origin of the observations.
authors.affiliation: University of Augsburg, Experimental Physics I, Augsburg, 86159, Germany.|Nanosystems Initiative Munich NIM, Schellingstr. 4, 80799 München, Germany.
authors.forename: Bernhard
authors.initials: B
authors.lastname: Fichtl
authors.affiliation: Medizinische und Biologische Physik, Technische Universität Dortmund, Otto-Hahn Str. 4, 44227 Dortmund, Germany.|University of Oxford, IBME Old Road Campus Research Building Oxford, OX3 7DQ, UK.
authors.forename: Shamit
authors.initials: S
authors.lastname: Shrivastava
authors.affiliation: Medizinische und Biologische Physik, Technische Universität Dortmund, Otto-Hahn Str. 4, 44227 Dortmund, Germany.
authors.forename: Matthias F
authors.initials: MF
authors.lastname: Schneider
mesh_terms: D000162:Acoustics; D006863:Hydrogen-Ion Concentration; D008055:Lipids / Q000737:chemistry*; D011522:Protons; D015398:Signal Transduction; D055672:Static Electricity; D013816:Thermodynamics; D053835:Unilamellar Liposomes / Q000737:chemistry*; D014494:Unithiol / Q000737:chemistry
chemical_list: D008055:Lipids; D011522:Protons; D053835:Unilamellar Liposomes; D014494:Unithiol