iLMO2 is able to suppress action potential firing in vitro.
(a) Left: fluorescence micrograph depicting dissociated cortical neurons expressing iLMO2. Right: bioluminescence image taken in the same field of view after addition of CTZ. Scale bar: 20 μm. (b) Representative voltage clamp recordings of a neuron expressing iLMO2 demonstrate hyperpolarizing outward photocurrents in response to CTZ (left, dashed line indicates time of CTZ addition) and green lamp illumination (right, green bar denotes period of illumination). Note that the outward current induced by CTZ coincides with an increase in luminescence (top left). (c) Average peak photocurrent response to CTZ and green lamp illumination in neurons expressing iLMO2 fusion protein (n = 8). (d) Representative current clamp recordings from neurons expressing iLMO2 demonstrate complete suppression of action potentials (evoked by 1 Hz threshold-level current injections) in response to CTZ (left, dashed line indicates time of CTZ addition) and green lamp illumination (right, green bar denotes period of illumination). A sustained hyperpolarizing response coincides with an increase in luminescence after CTZ addition. (e) Average percent inhibition of spontaneous (n = 3) and evoked (n = 6 for threshold-level current injections; n = 4 for supra-threshold) action potentials in cortical neurons expressing iLMO2. Error bars indicate standard error of the mean.