Effect of 3–10 μM Ca²⁺_o on tail current kinetics. (A) Sample records in 2 mM Ca²⁺_o (control and wash, left and right) and 10 μM Ca²⁺_o (middle), shown in 40-mV increments. 3 kHz Gaussian filter. Note biphasic tail currents at −20 and −60 mV (arrows). Tail currents in that voltage range are shown on an expanded time scale for 3 μM Ca²⁺_o (B) and 10 μM Ca²⁺_o (C), from a different cell. (D) Time constants from biexponential fits, from 3 cells in 3 μM Ca²⁺_o (filled circles) and 9 cells in 10 μM Ca²⁺_o (open squares). The dashed lines through the faster time constants are drawn for the 3.3-fold change in time constant expected from bimolecular kinetics. (E) The amplitudes of the fast and slow components to the biexponential fits.