Fig 8. Inverse relation between Ibasal and Ra arises from the decrease in Gα available for GIRK activation at higher Ibasal.
(A) Gα molecules/channel as a function of channel density. Data for Gα:GIRK and channel density were adopted from Tables 1 and 3 (oocytes) and Table 4 (neurons). To generate a continuous curve, the channel density-Gα relationship was arbitrary fitted with a hyperbolic decay function of the form Gα = Yo + a/x, where x is channel density and a is a constant. (B) Simulated relation between Ibasal and channel density. We utilized eqs 5–15 and solved them numerically in the 1–30 channels/μm2 range, using constant values of Gβγ:GIRK ratio (3.5 for oocytes and 3.4 for neurons) and the calculated values of Gα:GIRK from the fitted curves shown in A. (C) Simulated relationship of Ibasal and Ra, with variable Gα:GIRK (from A) and constant Gβγ:GIRK ratios. Simulations with 4 Gβγ and 2 Gα (red line) or 4 Gβγ and 4 Gα (green line) available for one GIRK1/2 channel at all densities did not adequately describe the data.