Muscle cells experience a nuclear buildup

In response to stimulation, muscle fibers can switch between two types: fast-twitch, used for quick movement; and slow-twitch, which are more resistant to fatigue. On page 27, Liu et al. find that the nuclear localization of a transcription factor may be the key to this switch.

Liu et al. applied electrical pulses to isolated adult murine muscle fibers, thus simulating fast-twitch and slow-twitch muscle stimulation in vitro. They then looked at the localization of the transcription factor NFATc, which has been implicated in muscle- and T-cell transcriptional regulation.

NFATc is cytoplasmic in unstimulated fast-twitch muscle fibers, but translocates to distinct nuclear foci when the fibers are exposed to kinase inhibitors or trains of electrical pulses at 10 Hz, simulating slow-twitch stimulation. Two conditions do not cause NFATc nuclear-translocation: simulated fast-twitch stimulation, and continuous 1 Hz stimulation, which...