Salt of the Earth: The Past and Present of the Na+/K+ Gradient

All existing organisms, bacteria, archaea, and eukaryotes maintain high levels of K+ over Na+ in their cytoplasm, sometimes at a great cost to the cell energy metabolism. The reasons for maintaining the Na+/K+ gradient have long remained obscure but have spawned diverse theories that advanced several areas of biochemistry, microbiology, and cell physiology.

I am going to briefly discuss some of these theories, including K+-dependence of some key enzymes, the role of Na+/K+ gradient in the transmission of the nerve impuls, proton-motive force buffering, sodium-based bioenergetics, and the origin of life in the K+-rich terrestrial environments.  I will then demonstrate the importance of the Na+/K+ gradient for bacterial pathogens and extremophiles, as well in the GPCR-mediated eukaryotic signaling. Finally, we are going to discuss the mechanistic reasons that underly the differential effects of Na+and K+ ions.