FIGURE 3.

Effects of PIP₂ on cyclic nucleotide-modulated SpIH channels. A, representative currents measured in response to a hyperpolarizing voltage step to −120 mV, followed by a voltage step to −40 mV from a holding voltage of 0 mV. Currents were measured in the absence of cyclic nucleotide (dashed black trace) and in the presence of 1 mm cGMP (dashed green trace), 1 mm cAMP (dashed red trace), cAMP + 10 μm diC₈-PIP₂ (solid red trace), and cGMP + 10 μm diC₈-PIP₂ (solid green trace). B, normalized G-V relationships for each condition in A. Tail currents at −40 mV were measured and normalized to the tail currents measured in the presence of 1 mm cAMP (dashed red trace in A). Solid and dotted curves represent fits to the data of the Boltzmann equation (see “Experimental Procedures”). Leak currents were subtracted as described under “Experimental Procedures.” C, bar graph showing the mean ± S.E. of the PIP₂-induced shift in the midpoint of the voltage dependence (ΔV_1/2 = V_1/2,PIP2 − V_1/2) for both cAMP- and cGMP-modulated channels (n = 5). D, bar graph showing the mean ± S.E. of the relative normalized conductance (G/G_max,cAMP) for cyclic nucleotide-modulated channels in the absence and presence of PIP₂ (n = 5). cA, cAMP; cG, cGMP.