An ER-retention/retrieval sequence at the C-terminus of β4 inhibits the surface expression of BKα and β4.

(A) Schematic of the mutant β4 constructs showing the C-terminal amino acids. (B) Fluorescence from binding of cell-impermeable dye to cell-surface BKα channels in cells transfected with FAP-BKα (red) and GFP (green). (C) Same as (B) but in cells transfected with FAP-BKα and wild-type β4. (D) Same as (B) but in cells transfected with FAP-BKα and β4-Ala. (E) Same as (B) but in cells transfected with FAP-BKα and β4-polySer. Scale bar = 20 µm (B–E). (F) Mean intensity of surface fluorescence for β4 constructs normalized to fluorescence from cells transfected with FAP-BKα alone. (G) Histogram showing distribution of fluorescence intensity in cells transfected with FAP-BKα alone (red), FAP-BKα+β4-Ala (green) and FAP-BKα+β4-polySer (blue). Scale bar: 20 µm (B–E).