FIGURE 6.

Effects of 10 μm PIP₂ on cyclic nucleotide modulation of mutant SpIH channels (R475C, R478C, and K482C). A, C, and E, 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, D, and F, normalized G-V relationships for each mutant. All currents were measured from tail currents at −40 mV and normalized (see “Experimental Procedures”). Data in the absence of PIP₂ are shown as open circles, and those in the presence of PIP₂ are shown as closed circles (see legend in B). Solid and dotted curves represent fits to the data of the Boltzmann equation (see “Experimental Procedures”). nn, no nucleotide; cA, cAMP; cG, cGMP.