Figure 4. Charging membrane currents in mature RGC.

Charging currents in two different cells were generated by −10 mV steps superimposed on −70 mV holding voltage. Inward current is positive. A illustrates current measured under physiological salt solutions. The experimental data (○) cannot be fitted by a single exponential function. The continuous line is a single exponential that describes the charging of the soma's electrical elements of the cell shown (details in text). The time axis is normalized by dividing time by the time constant of the soma's charging, in this case τ = 0.19 ms. B illustrates current measured in a different mature RGC in the presence of modified intra- and extracellular solution designed to block all known voltage-gated currents in the cell. The experimental data (○) are well fitted by a single exponential function (continuous line) of time constant τ = 2.38 ms (coefficient of correlation = 0.97).