Increase in the extracellular K⁺ concentration decreases the electric currents passing through the Alka channel (A), indicating that K⁺ binding induces a state transition to the closed state in Alka (B). Credit: Takushi Shimomura Researchers from the National Institute for Physiological Sciences, Nagoya City University, and Tokyo Metropolitan Institute of Medical Science in Japan have identified the first animal ion channel molecules that open and close in response to extracellular potassium ions (K⁺). The paper is published in the journal Nature Communications . Potassium ions (K⁺) are essential for all cells and living organisms. Scientists have long believed that K⁺ merely passes through ion channels and transporters, rather than acting as an extracellular ligand or molecular "switch." Indeed, there had been no clear evidence that K⁺ functions as a ligand for membrane proteins in animals or plants—until now.…