Whole-cell patch-clamp recordings from cultured RGC neurons were performed at room temperature in an isotonic saline solution (in mM: NaCl 125, NaHCO3 25, KCl 2.5, NaH2PO4 1.25, glucose 25, MgCl2 1, CaCl2 2). Patch electrodes with resistances of 2.5–3.5 MΩ were pulled from thick-walled borosilicate glass capillaries and were filled with an internal solution containing (in mM) potassium gluconate 130, NaCl 4, EGTA 5, CaCl2 0.5, 10 HEPES, MgATP 4, Na2GTP 0.5 (pH 7.2 with KOH). Miniature excitatory postsynaptic currents (mEPSCs) were recorded in TTX (1 μM, Alomone) from a holding potential of -70 mV. Series resistance was monitored throughout the recording and was <20 MΩ. Data were sampled at 50 kHz and filtered at 1 kHz using pClamp 9.2, and offline analysis of mEPSCs was performed using Clampfit 10.3 (Molecular Devices).
