A, comparison of the effects of 0.25 mm TEA (middle panel) and 100 nmα-DTX (lower panel) on membrane currents of a HAC. Currents produced by potential steps to –40, –20, 0, +40, +60 and +80 mV are shown (selected voltages are indicated). B, mean step I–V (current density) relations for 16 HACs, in the presence of 0.25 mm TEA (filled circles) and in the presence of TEA and 125 nmα-DTX (open triangles). C, best-fit of a Boltzmann function (see text) to the α-DTX-sensitive current.