tmFRET between R18 and Co²⁺-C18-NTA in inside-out patches from a Xenopus oocyte. (A) Bright-field and epifluorescence images from a representative patch. Fluorescence images from patches with either 0 or 1 µM Co²⁺ before (left) or after (middle) application of C18-NTA and after 20 mM EDTA (right). Scale bar in top left image applies to all images and is 20 µm. (B) Patch fluorescence in Co²⁺ was normalized to patch fluorescence in EDTA before and after C18-NTA (n = 4). Mean (lines) and individual (points) patch values are shown. Asterisk indicates significance at P < 0.05.