Protons at the speed of sound: Specific biological signaling from physics

TL;DR

This study demonstrates that localized pH pulses can propagate rapidly along lipid interfaces, inducing mechanical and electrical signals that could serve as a new physical mechanism for biological communication.

Contribution

It reveals the existence of fast protonic sound waves at lipid interfaces, linking pH changes to mechanical and electrical signals for biological signaling.

Findings

pH pulses propagate at speeds up to 1.4 m/s

Transient pH changes of 0.6 units observed at the interface

Mechanical and electrical changes accompany the pulses

Abstract

Local changes in pH are known to significantly alter the state and activity of proteins and in particular enzymes. pH variations induced by pulses propagating along soft interfaces (e.g. the lipid bilayer) would therefore constitute an important pillar towards a new physical mechanism of biochemical regulation and biological signaling. Here we investigate the pH-induced physical perturbation of a lipid interface and the physiochemical nature of the subsequent acoustic propagation. Pulses are stimulated by local acidification of a lipid monolayer and propagate, in analogy to sound, at velocities controlled by the two-dimensional compressibility of the interface. With transient local pH changes of 0.6 units 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 up to 8 mN/m and 100 mV 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. When combined with an enzymatic pH-optimum, the proposed communication can be very specific, thus providing a new physical basis for intra- and intercellular signaling via two-dimensional sound waves at interfaces.