Figure 1. Biophysical properties of AMPA receptor-mediated ipRGC-driven EPSCs of DACs. α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate (AMPA) receptor-mediated light-induced excitatory postsynaptic currents (EPSCs) of dopaminergic amacrine cells (DACs) were recorded with a whole-cell patch-clamp configuration in Opn4-function-only flatmount retinas at holding potentials of 40 mV and −60 mV without (A) and with (B) 100 µM spermine in the pipette solution. AMPA receptor-mediated light-induced EPSCs were isolated in the presence of a cocktail of antagonists (50 µM D-AP5 for N-methyl-D-aspartate (NMDA) receptors, 0.3 µM ACET for Kainate receptors, 20 µM GABAzine for GABA_A receptors, 50 µM TPMPA for GABA_C receptors, and 1.0 µM strychnine for glycine receptors). The stimulation bar shows the timing of a 470 nm light pulse (duration: 3 s; intensity: 4.7 × 10¹³ photons·cm⁻²·s⁻¹). In (C), current-voltage relationships of AMPA receptor-mediated light-induced EPSCs from DACs including the cells in (A) and (B) were constructed (see the Methods section) without (triangles, mean ± standard error of the mean (SEM), n=4) and with (circles, mean ± SEM, n=10) spermine. The curves indicate that DAC AMPA receptor-mediated light-induced EPSCs exhibit an outward rectification, and this rectification was not changed by spermine. The rectification index (RI) of the DAC AMPA receptor-mediated light-induced EPSCs was calculated (see the Methods section), but it was not affected by spermine (D, mean ± SEM, n=4 for spermine free, n=10 for spermine, n.s. p>0.05, Student t test).