Fig. 1. Cbln1, NRX1, and cell-to-cell contacts are required for agonist-dependent gating of delta receptors.

(A) Schematic drawing of HEK-293T cell cluster recordings. (B to E) Electrophysiological measurements of cells expressing GluD2, Cbln1, and NRX1. Representative currents activated by (B) 10 mM glycine, d-serine, glutamate, or no ligand (buffer); (C) different concentrations of glycine; and (D) different concentrations of d-serine. (E) Normalized concentration-response curves for glycine (EC₅₀ = 1.07 ± 0.06 mM) and d-serine (EC₅₀ = 2.9 ± 0.13 mM); number of measurements for each concentration is provided in table S1. (F) Current-voltage (I-V) relationship for glycine- and d-serine–mediated currents. (G) Representative currents showing inhibition of 2 mM glycine-mediated currents by 500 μM DCKA. (H) Normalized concentration-response curves showing DCKA inhibition with 500 μM glycine (red) and 2 mM glycine (blue); the number of measurements for each concentration is provided in table S1. (I) Glycine-activated currents in cells expressing GluD2 with either Cbln1 or NRX1 in clusters, Cbln4 and NRX1 in clusters, or Cbln1 and NRX1 in isolated cells compared to GluD2 with Cbln1 and NRX1 in clusters.