FIGURE 4.

The C-terminal domain mediates PIP₂ inhibition and the transmembrane domain mediates PIP₂-induced positive shift in voltage. A and B, representative currents recorded from SpIH_ΔC channels lacking the C-terminal region (deleted amino acids 471–767) in response to voltage steps between −40 and −130 mV in the absence and presence of 30 μm diC₈-PIP₂. The red trace indicates currents measured at the same voltage, −70 mV. C, G-V relationships for SpIH_ΔC measured from tail currents at −40 mV in the absence of PIP₂ (black circles), in the presence of 30 μm diC₈-PIP₂ (gray circles), and after PIP₂ was washed out (white circles). The curves represent fits of the Boltzmann equation to the data. D and E, representative currents recorded from C-terminal deleted SpIH_ΔNC channels (deleted amino acids 1–160 and 471–767) in response to voltage steps between −40 and −130 mV in the absence and presence of 30 μm diC₈-PIP₂. The red trace indicates currents measured at the same voltage, −90 mV. F, G-V relationships for SpIH_ΔNC measured from tail currents at −90 mV in the absence of PIP₂ (black circles), in the presence of 30 μm diC₈-PIP₂ (gray circles), and after PIP₂ was washed out (white circles). G, change in voltage dependence as determined for the difference in V_1/2 before and after modulation by PIP₂ (ΔV_1/2). H, normalized conductance in diC₈-PIP₂ for SpIH_ΔC and SpIH_ΔNC.