A genetically encoded sensor of ionic stress links cellular proton dynamics to sleep.

Abstract

Although biosensors for specific cellular ions are widely available, real-time monitoring of overall ionic strength in living organisms remains challenging. Here, we present a genetically encoded nuclear translocation ionic sensor (GENTIS) that enables direct visualization of ionic stress in vivo. Using this sensor alongside longitudinal tracking via an automated microfluidic platform, we find that <i>Caenorhabditis elegans</i> larvae experience highly synchronized, rhythmic elevations in intestinal ionic strength during the molt, a stage during which developmentally timed sleep occurs. Cytosolic proton accumulation through inhibition of vacuolar-type adenosine triphosphatases (V-ATPases) triggers GENTIS nuclear translocation and evokes behavioral quiescence, characterized by reduced feeding, locomotion, and activation of sleep-active neurons. Apical membrane V-ATPases naturally undergo disassembly during molting and stress, conditions that cause proton accumulation and sleep. Notably, this proton-linked sleep is suppressed by proton buffering with ammonium. Together, these findings establish GENTIS as a powerful tool for tracking ionic strength dynamics in vivo and reveal that proton ionic rhythms contribute to the regulation of sleep.