Figure 4. Construct designs and data summary from experiments that explore a proposed Cl⁻‐binding motif upstream of the cationic cluster.

A, designs of constructs. In addition to Δ9_40–48 (see Fig. 1A), we created 2 additional constructs, based on NBCe1‐B (B_WT). B, HCO₃ ⁻‐dependent conductances (G _HCO3) computed between −20 and +20 mV of I−V relationships. G _HCO3 values were normalized to the G _HCO3 from an oocyte – studied the same day – expressing ∆9_40–48. The n for each group (i.e. construct) is 6. The asterisk indicates significant difference, by one‐way ANOVA followed by post hoc Tukey's comparison. C, surface‐biotinylation of proteins 5 days after cRNA injection (i.e. 1 day after electrophysiological experiments), and analysis by western blotting. The 5 lanes (the H₂O is virtually blank) of the blot are aligned with the labels in B. This blot is representative of two trials, which confirm that GVAVP and AVHVA are present at relatively low abundance in the plasma membrane. Note that 3 lanes between ∆9_40–48 and GVAVP were deleted from the blot image in order to create the one‐to‐one correspondence between panels B and C. D, HCO₃ ⁻‐dependent conductances (G _HCO3) from oocytes expressing four different constructs, without or with super‐IRBIT (sIRBIT). G _HCO3 values were normalized to the G _HCO3 from an oocyte – studied the same day – expressing ∆9_40–48 without sIRBIT. The n for each group is 3–6. ^†Pairs are significantly different in a one‐tailed, unpaired t test. NS, not significant. E, surface‐biotinylation of proteins 4 days after cRNA injection, and analysis by western blotting. B_WT and GVAVP were expressed without and with sIRBIT.