Fig. 7.

Mean effect of α1B deletions and mutations on Gβγ modulation in COS-7 cells. A, The P2/P1 ratio was determined in COS-7 cells overexpressing Gβ1γ2, from current amplitudes during steps to −10 mV before and after a depolarizing prepulse (+120 mV, 100 msec), for the same N-terminal deletions and point mutations shown in Figure 5. Comparison is made with α1B in the absence of Gβγ, recorded with 1 mm GDPβS in the patch pipette (1). The value [(P2/P1) − 1] is plotted, which will be 0 if there is no facilitation. B, The activation V₅₀ was determined for the same constructs coexpressed with Gβ1γ2, and compared to the value for α1B in the absence of Gβγ, recorded with 1 mm GDPβS in the patch pipette (1). The dashed lines are 1 SEM more positive than the mean value for α1B (1), and 1 SEM more negative than the mean value for α1B/Gβγ (2). C,Correlation between Δ activation V₅₀ (the data given in B, after subtraction of theV₅₀ for α1B) on the y-axis, and the data from Figure 5C (percentage inhibition ofI_Ba by 100 nm quinpirole), on the x-axis. The numbers identifying the constructs refer to the bars in A and B. Regression analysis (dotted line) gives a coefficient,r of 0.92 (p < 0.001). The data divide into a group of modulated and a group of nonmodulated constructs, as identified, except for constructs 14 (I49A) and 9 (YKQ→AAA).