Figure 2. Sequestering Gβγ opens the TRPM1 channel (under dark adaptation).

(A) The protocol of a dark adapted experiment (illustrated with a record from a cell dialyzed with myr-Gα_o): 0.5 sec after break-in, a 2 s voltage ramp was applied, and 10.5 sec after break-in, a 50 msec light (3.8 × 10⁴ photons μm⁻² s⁻¹) was flashed. This cycle was repeated every 35 s. The 1^st sweep is shown in black, the 5^th sweep in gray. (B) The dark inward current was measured by averaging the currents over 0.5 sec before the light flash (indicated by blue rectangular boxes in A). Black trace is from the 1^st sweep, gray is from the 5^th. The average holding current at the 1^st sweep is indicated by a red line, and that at the 5^th by a pink line. The difference is indicated by the delta symbol on the right. (C) Slope conductance was computed from the current responses to the voltage ramp (shown in red boxes in A) between −95 mV to −65 mV (the linear range). First ramp is in black, 5^th in gray. The slopes for these records are shown in red and pink, correspondingly. (D) Quantitative analysis of changes in the dark holding currents for five different conditions: control, 100 nM myrGα_o, 9 μM phosducin, 40 nM myrGα_ο−QL, and 150–300 nM His-Gα_o. When channels are opening, the inward current increases (has a more negative value) and the difference between the 5^th and the 1^st time points is negative. (E) Quantitative analysis of changes in slope conductance for each of the above conditions. *indicates a significant difference (p < 0.05) between the 1^st and 5^th time points, and **indicates a highly significant difference (p < 0.01).