Figure 5. Physical continuity of the EC loop between TM1 and TM2 is essential to confer the characteristic phenotype of β1-containing BK channel complexes.

(A) Cartoons depicting two hβ1/hβ4 chimeric constructs termed “N-half” and “C-half”, obtained by cleaving the EC loop between TM1 and TM2 in the β4TMs₁ chimera. Regions of β1 and β4 are given in black and grey, respectively. When expressed together (panels C-G and main text), “N-half” and “C-half” chimera have been labeled as construct 8. (B) Western blots reflecting the surface presence of N-half and C-half, when co-expressed with cbv1, obtained by surface biotinylation of Xenopus oocytes expressing cbv1+N-half+C-half complexes. Blot image where left and right lanes contain samples from uninjected and N-half+C-half chimera-injected oocytes, respectively. (C) Representative traces of macroscopic current recordings obtained from I/O oocyte membrane patches expressing construct 8; Ca²⁺ _i = 10 µM. (D) Averaged G/G_max-V plots from cbv1, cbv1+β1, cbv1+β4, and cbv1+construct 8; Ca²⁺ _i = 10 µM. Averaged V_half (E), activation (F) and deactivation (G) time constants (τ_act, τ_deact, respectively) obtained cbv1, cbv1+β1, cbv1+β4, and cbv1+construct 8. *Different from cbv1 (P<0.05); ^#Different from cbv1+β1 (P<0.05). Error bars show SEM; each point represents the average of ≥4 patches.