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Imaging chloride homeostasis in live neurons.
Arslanbaeva L.R., Paredes J.M., Idilli A.I., Arosio D.
Intracellular chloride and $pH$ are fundamental regulators of neuronal excitability and they are often co-modulated during excitation-inhibition activity. Their role is thus critical in several human diseases, and neurodevelopmental disorders. Continuous observation of multi-ion homeostasis requires simultaneous measurements in multiple neurons $in vivo$. Combining random mutagenesis screening, protein engineering and advanced imaging, we developed new chloride-sensitive GFP mutants, established accurate ratiometric imaging procedures and demonstrated combined imaging of intra-neuronal pH and chloride. By extending the use of genetically encoded fluorescent biosensors, we measured chloride ion concentration in living neurons with unprecedented resolution. Dynamic alterations in the fluxes of protons and chloride ions induced by epilectic activity will be shown to induce intracellular acidification and chloride accumulation. Intracellular chloride changes will be also shown to occur physiologically during brain development in mice. We expect out methods will allow a wider adoption of quantitative chloride imaging to study the combined role of proton and chloride ions in the cellular physiology and physiopathology.