Fig. 2.

CaMKIIα-CaM association during sLTP induction. a Representative fluorescence lifetime images of CaMKIIα-CaM association sensor during glutamate uncaging at 0.49 Hz. Warmer colors indicate lower fluorescence lifetime, corresponding to a higher binding fraction of mCherry-CaM to mEGFP-CaMKIIα. Scale bar, 1 µm. b Time course of CaMKIIα-CaM association in a stimulated spine (black) and nearby dendrite (blue). Analyzed from images in a. Black dots represent uncaging pulses. c Expanded view of the rising phase (left) and the decay phase (right) of b. d Averaged change in CaMKIIα-CaM association in stimulated spines (black) and nearby dendrite (blue) (n = 27 spines/9 neurons). The orange curve indicates the decay of binding fraction change obtained by curve fitting of a double-exponential function: B(t) = B₀ [P_fast·exp(–t/τ_fast) + P_slow·exp(–t/τ_slow)], where B₀ is the initial binding fraction change, τ_fast and τ_slow are the fast and slow decay time constants and P_fast and P_slow are the respective populations. The time constants are obtained as τ_fast = 3.2 ± 0.6 s (P_fast = 71%) and τ_slow = 572 ± 843 s (P_slow = 29%). e Expanded view of the rising phase (left) and the decay phase (right) of d. f Average time course of CaMKIIα-CaM association for a mutant mEGFP-CaMKIIα^T305D/T306D in which the Thr305 and Thr306 are mutated to aspartate. The mutation precludes Ca²⁺/CaM binding in the stimulated spine during glutamate uncaging at 0.49 Hz (purple; n = 34 spines/5 neurons). The data for CaMKIIα^WT (black) are from c for the comparison. All data are shown in mean ± sem, and sem of time constants is obtained by bootstrapping