Characterization of G-CaMPs <i>in vitro</i> and in HeLa cells.

<p> <b>A</b>, Schematic representation. Mutations are indicated with respect to G-CaMP2. RSET and M13 are tags that encode hexahistidine and a target peptide for Ca²⁺-bound CaM derived from MLCK, respectively. The amino-acid numbers of EGFP and CaM are indicated in parentheses. <b>B</b>, Dynamic range (<i>F</i>_max/<i>F</i>_min) and Ca²⁺ affinity (<i>K</i>_d). Error bars, s.d. (<i>n</i> = 3 each). <b>C</b>, Ca²⁺ titration curve. Curves were fit according to the Hill equation. <i>K</i>_d is shown in <b>B</b>. <b>D</b>, Normalized fluorescence and absorbance (inset) spectra of G-CaMP6 and G-CaMP8 in 1 µM Ca²⁺ or 1 mM EGTA. <b>E</b>, Fluorescence images of HeLa cells expressing G-CaMPs. Bars, 30 µm. <b>F</b>, Time course of the changes (Δ<i>F</i>/<i>F</i>) in G-CaMP fluorescence in response to 100 µM ATP. Error bars, s.d. <b>G</b>, Baseline fluorescence and peak responses (Δ<i>F</i>/<i>F</i>) to ATP application in HeLa cells.