Regulation of GIRK1/4 channel activity by Gα-FP constructs and their constitutively active mutants. The graphs show the effects of overexpression of FP-tagged Gαi1 constructs on GIRK1/4 channel current in HEK293 cells in the absence and presence of overexpressed Gβ1γ2 dimers. A, GAP43-CFP-Gαi1. B, Gαi1-L91-YFP. The graphs show current normalized by cell surface area (characterized by capacitance) (picoamperes/picofarad (pA/pF)) in non-transfected cells (white bars); cells transfected with GIRK1-C-CFP and GIRK4 constructs (light gray bars); GIRK1-C-CFP, GIRK4, and Gαi1-FP (medium gray bars); GIRK1-C-CFP, GIRK4, Gβ1 (or Gβ1-YFP), and Gγ2 (black bars); GIRK1-C-CFP, GIRK4, Gαi1-FP, Gβ1 (or Gβ1-YFP), and Gγ2 (horizontally hatched bars); GIRK1-C-CFP, GIRK4, Gαi1-FP, Gβ1 (or Gβ1-YFP), Gγ2, and α2aAR stimulated by 1 μm NE (diagonally hatched bars); GIRK1-C-CFP, GIRK4, a constitutively active Gαi1-FP mutant (GAP43-CFP-Gαi1(Q204L), or Gαi1(Q204L)-YFP) (vertically hatched bars); and GIRK1-C-CFP, GIRK4, a constitutively active Gαi1-FP mutant, Gβ1 (or Gβ1-YFP), and Gγ2 (crossed diagonally hatched bars) constructs. Error bars represent mean − S.E.