A, in muscle fibres expressing wt HDAC4-GFP, Epac activator 8-CPT caused a net nuclear efflux of HDAC4-GFP or HDAC4 (S265/266A)-GFP. B, in the presence of the CaMKII inhibitor KN-93, 8-CPT did not affect the nuclear localization of wt HDAC4-GFP or HDAC4 (S265/266A)-GFP. C, if muscle fibres were incubated with the calcium chelator BAPTA-AM, addition of 8-CPT did not affect the nuclear localization of wt HDAC4-GFP or HDAC4 (S265/266A)-GFP. Data are from 16 nuclei of 10 fibres of 2 mice for HDAC4-GFP, and 14 nuclei of 11 fibres of 2 mice for HDAC4 (S265/266A)-GFP in A; 9 nuclei of 5 fibres of 1 mouse for HDAC4-GFP, and 12 nuclei of 12 fibres for HDAC4 (S265/266A)-GFP of 2 mice in B; and 13 nuclei of 9 fibres of 2 mice for HDAC4-GFP, and 17 nuclei of 10 fibres of 2 mice for HDAC4 (S265/266A)-GFP in C. D, summary of net flux rate using data of linear fit from A, B and C. *P < 0.01, compared with the group of fibres with 8-CPT alone.