Supplementary Figure 6: Activation of eArch3.0 in cultured hippocampal neurons leads to an increase in intracellular pH that is attenuated by a lactate-containing buffer.

(a) Representative two-photon images depicting mean BCECF fluorescence before (top) and during (bottom) 590 nm illumination in control neurons (left) and in neurons expressing eNpHR3.0 (middle) and eArch3.0 (right). (b) Time course of changes in fluorescence of the intracellular pH indicator BCECF. ΔF/F for non-transduced neurons (black, n = 3 imaged regions), eNpHR3.0-expressing neurons (blue, n = 4 imaged regions), eArch3.0-expressing neurons (red, n = 3 imaged regions) and eArch3.0-expressing neurons recorded in an extracellular buffer containing L-lactate (50 mM, orange, n = 3 imaged regions) under the same light delivery protocol as in Fig. 3. (c) Average ΔF/F during baseline and light-on periods shown in b. (d) Proposed model of eArch3.0-mediated changes in synaptic transmission. Activation of eArch3.0 using yellow light leads to increased intra-synaptic pH, which induces calcium influx into the presynaptic terminal, thus causing increased spontaneous release onto post-synaptic excitatory (red) and inhibitory (blue) neurons. Increased activity of local-circuit interneurons might lead to inhibition onto neurons that do not receive input from the axonal inputs targeted with eArch3.0. Error bars and shaded regions indicate s.e.m. (* P < 0.05; see Supplementary Table 1 for statistics).