Figure 3. The effect of eOPN3 on neurotransmitter release is sensitive to pharmacological inhibition of G_i/o-protein signaling but is not affected by a GIRK channel blocker.

(A) Action potential-evoked EPSCs in control neurons (upper row) were suppressed both by the GABA_BR agonist baclofen (30 μM) and by subsequent activation of eOPN3 with 550 nm light (500 ms, 40 mW·mm ²). In pertussis toxin (PTX)-treated neurons (20-26 h pre-treatment, 0.5 μg-mL ‘, bottom row), both baclofen and eOPN3 largely failed to suppress release.

(B) Averaged time-course of EPSCs recorded in neurons treated with PTX (open circles; n = 5) and neurons not treated with PTX (filled circles; n = 9; p = 3·10 ⁴ Kruskal-Wallis test followed by Dunn’s multiple comparison tests: p < 0.05 for Bacl versus PTX Bacl, Light versus PTX Bacl and Light versus PTX Light).

(C) Illumination of eOPN3-expressing neurons evokes robust outward currents (45.5 ± 8.1 pA, n = 5), which are abolished in the presence of the GIRK channel blocker SCH23390 (10 μM, 1.2 ± 3.5 pA; n = 5; p = 1·10 ³ unpaired, two-tailed Student’s t test).

(D) The extent and time-course of EPSC suppression by eOPN3 activation is not affected by the GIRK channel blocker SCH23390 (filled circles: ctrl recordings, n = 5; open circles: SCH23390, n = 5; p = 0.59 unpaired, two-tailed Student’s t test). Plots show individual data points and average ± SEM.