A genetically-encoded chloride and pH sensor for dissociating ion dynamics in the nervous system

Within the nervous system, intracellular Cl(−) and pH regulate fundamental processes including cell proliferation, metabolism, synaptic transmission, and network excitability. Cl(−) and pH are often co-regulated, and network activity results in the movement of both Cl(−) and H(+). Tools to accurately measure these ions are crucial for understanding their role under physiological and pathological conditions. Although genetically-encoded Cl(−) and pH sensors have been described previously, these either lack ion specificity or are unsuitable for neuronal use. Here we present ClopHensorN—a new genetically-encoded ratiometric Cl(−) and pH sensor that is optimized for the nervous system. We demonstrate the ability of ClopHensorN to dissociate and simultaneously quantify Cl(−) and H(+) concentrations under a variety of conditions. In addition, we establish the sensor's utility by characterizing activity-dependent ion dynamics in hippocampal neurons.