Figure 5.

Blockage by extracellular Ca²⁺ of A3 and A3_T369S channels. Dose-response relations at -80 mV (left) and +80 mV (right) for the blockage of monovalent current by extracellular Ca²⁺ ions for A3 (filled circles) and A3_T369S (open circles) channels are shown. Solid lines were calculated with the equation I/I_max = (1 - a) K_i/(K_i + c) + a, where c is Ca²⁺ concentration; K_i, concentration of half-maximal inhibition; and a, residual current nonsusceptible to blocking, using the following K_i values: 387.9 ± 36.0 μm (+80 mV) and 9.9 ± 1.4 μm (-80 mV) (A3; N = 6); and 381.4 ± 85.4 μm (+80 mV) and 289.5 ± 59.1 μm (-80 mV) (A3_T369S; N = 5).