Supplementary Figures

Supplementary Fig. S1: Normalized excitation and emission spectra of Alexa488N, TAC-Rh and Alexa647N. Supplementary Fig. S2: UV-Vis absorption spectrum of ssDNA-TAC-Rh. Supplementary Fig. S8: 2-IM profiles of HEK 293T cells clamped at pH 6.0. Supplementary Fig. S9: Comparison of <em>in vitro</em> and <em>in cellulo</em> clamping. A-B,<em> In vitro </em>and <em>in cellulo </em>response of <em>pHlicKer </em>given by fold change (FC) of (A) D/A from pH 6.0 - 6.6 at 0.1 mM [K⁺] and (B) O/R ratios from 0.1 - 140 mM [K⁺] at the indicated pH.<em> C</em>, <em>In vitro </em>and <em>in cellulo K</em>d values of <em>pHlicKer </em>determined at the indicated pH. D, O/R values of <em>pHlicKer</em> at pH 6.6 as a function of [K⁺] obtained <em>in vitro </em>and <em>in cellulo</em>. Supplementary Fig. S10: A) Normalized ratio of fluorescence intensity of donor to that of acceptor (D/A) of <em>pHlicKer</em>^{<em>Biotin</em>} on beads as a function of pH. B) <em>pHlicKer</em>^{<em>Biotin</em>}<em> K</em>d as a function of pH. Supplementary Fig. S11B: Pearson’s correlation coefficient (PCC) of colocalization (CL) and pixel shift (PS) of HEK 293T cells expressing Kv11.1 immunostained for anti-Kv_11.1 and anti-58K that marks the trans Golgi network. . Supplementary Fig. S12B: Pearson’s correlation coefficient (PCC) of colocalization (CL) and pixel shift (PS) of HEK 293T cells expressing Kv_11.1 immunostained for anti-Kv_11.1 and anti-Transferrin receptor that marks recycling endosomes. Supplementary Fig. S13: A-B, [K⁺]_RE and C-D, [K⁺]_TGN values in UT cells in the absence and presence of cisapride. Supplementary Fig. S14: [K⁺]_TGN values in UT and WT cells. Supplementary Table 1: Propagation of error assessed by a blind test.