A Scenario For The Origin Of Life: Volume Regulation By Bacteriorhodopsin Required Extremely Voltage Sensitive Na-Channels And Very Selective K-Channels

Abstract The osmotic activity produced by internal, non‐permeable, anionic nucleic acids and metabolites causes a persistent and life‐threatening cell swelling, or cellular edema, produced by the Gibbs‐Donnan effect. This evolutionary‐critical osmotic challenge must have been resolved by LUCA or its ancestors, but we lack a cell‐physiology look into the biophysical constraints to the solutions. Like mycoplasma, early cells conceivably preserved their volume with Cl − , Na + , and K + ‐channels, Na + /H + ‐exchangers, and a light‐dependent bacteriorhodopsin‐like H + ‐pump. Here, I simulated protocells having these ionic‐permeabilities and inhabiting an oceanic pond before the Great‐Oxygenation‐Event . Protocells showed better volume control and stable resting potentials at lower external pH and higher temperatures, favoring a certain type of extremophile life. Prevention of Na + ‐influx at night, with low bacteriorhodopsin activity, required deep shutdown of highly voltage‐sensitive Na + ‐channels and extremely selective K + ‐channels, two conserved features essential for modern neuronal encoding. The Gibbs‐Donnan effect universality implies that extraterrestrial cells, if they exist, may reveal similar volume‐controlling mechanisms.