Figure 2.

Use-dependent activation is observed in Kv1.2 but not other Kv1 channel subtypes. A, LM cells expressing WT Kv1.2 or Kv1.2[T252R] channels (as indicated) were subjected to 20 Hz trains of repetitive depolarizations (60 mV for 10 ms, −80 mV for 40 ms). Exemplar currents generated from 50 pulses illustrate the slow and fast Kv1.2 phenotypes, along with exclusively fast currents generated by Kv1.2[T252R] channels. B, Similar protocols were performed with numerous Kv1 family channels. Percentage use-dependent activation was calculated (inset) as the difference in peak current between the first pulse to 60 mV and currents elicited at the end of the depolarizing train (n = 176 for WT Kv1.2, >20 for Kv1.2[T252R] and other Kv1 subtypes). Sample sweeps show pulses 1 (colored) and 50 (black) from the pulse train. Scatter/box plots illustrate the variability in percentage use-dependent activation for each channel type. * Note that Kv1.1 and Kv1.4 did not express well, and were expressed as chimeras with the distal N-terminus of Kv1.5 (see Methods) - this manipulation leaves the S2–S3 linker, previously identified as critical for use-dependent activation, unchanged. Overall, significant use-dependent activation is only observed for Kv1.2 channels. C, Structural localization of Kv1.2 residue T252 in the intracellular S2–S3 linker is highlighted on the Kv1.2 paddle chimera structure. D, Sequence alignment of the S2–S3 linker for numerous Kv1 channel subtypes, illustrating that a Thr at this position is only present in Kv1.2.