Voltage-gated sodium channels as non-photonic sensors for membrane-delimited reactive species
Reactive species (RS) play important roles in vital physiological processes. However, excessive RS damages cells and may contribute to the onset of several diseases. Therefore, there is a clear demand for sensitive probes that precisely monitor cellular RS with a high spatio-temporal resolution to understand the multifaceted role of RS in redox biology. Despite the fact that genetically encoded redox reporters are promising tools for quantitative and dynamic observation of RS, the excitation light used to read-out the fluorescence of these proteins can lead to irreversible modification of cell constituents. Herein, we have developed two RS sensing tools, roNaV1 and roNaV2, based on rat NaV1.4 (SCN4A) for monitoring membrane-delimited reactive species in a non-photonic and ratiometric fashion. Oxidative modification of a single cysteine (roNaV1) and a single selenocysteine (roNaV2) in the inactivation motif of channel-based RS sensors results in a marked loss of inactivation that can be monitored by repeatedly recording currents mediated by channels on a real-time scale with high precision. Advantageously, channel-based RS sensors do not need excitation light, and hence, can be used to detect phototoxic cellular modifications. Notably, roNaV2 is the first reported selenocysteine containing Na+ channel, which was adequately expressed in a heterologous expression system. Channel-based RS sensors (roNaV1 and roNaV2) are not only rapid, sensitive, ratiometric, and light independent membrane-based RS sensors but also gateable (switchable) by the membrane voltage, allowing for complex experimental settings in which membrane-delimited occurrence of reactive species has to be monitored.