Figure 1. Capacitance measurements from mouse AII amacrine cells.

A: Schematic diagram of an AII amacrine cell (AII-AC) showing the thick primary dendrite, its lobular appendages (site of glycinergic active zones) and the distal arboreal dendrites (site of rod bipolar cell input and gap junctions). B: Fluorescence image of an AII-AC in a mouse retinal slice. The cell was filled with Alexa fluor-488 (100 μM) via a patch pipette on the soma. The dashed lines demarcate the boundaries of different retinal layers. Scale bar = 10 μm. C: The AII-AC shows a bi-exponential capacitative current decay (fit = blue curve) and a steady-state current during a 10 mV hyperpolarizing voltage step. The time constants are shown as well as the input resistance (R_i), which is calculated from the steady-state current. D: Depolarization-evoked exocytosis from a mouse AII-AC. A membrane capacitance (C_m) change was evoked by a depolarizing step. Experiments were conducted at near physiological temperature (~30°C). The stimulus protocol was composed of three segments: a 2 kHz sinusoidal voltage of 30 mV peak-to-peak in amplitude superposed on the holding potential of −80 mV before and after a 100 ms depolarizing step from −80 mV to −10 mV, which evoked a Ca²⁺ current. The 2 kHz sine wave was used to measure changes in C_m that reflect the exocytosis of synaptic vesicles. Note the absence of significant changes in series resistance (R_s) and membrane resistance (R_m). E: Voltage dependence of Ca²⁺ current and membrane capacitance change (ΔC_m) in AII-ACs. The ΔC_m was evoked by single depolarizing pulse of 200 ms duration, from −80 mV to various membrane potentials (n=5; with temperature at ~28°C). Mean and SEM values are mark ed in solid red circles, whereas open red circles denote individual values. The Ca²⁺ current was evoked by a voltage ramp from −60 to +30 mV for 100 ms (blue trace; average of 5 cells). The Ca²⁺ currents and ΔC_m are highly correlated for the different membrane potentials.