KCNE1 slows KCNQ1 activation several-fold, and there are ongoing discussions about the precise mechanisms underlying this. In a study in which KCNQ1 voltage sensor movement was monitored by site-directed fluorimetry and also by measuring the charge displacement associated with movement of charges within the S4 segment of the voltage sensor (gating current),  KCNE1 was found to slow S4 movement so much that the gating current was no longer measurable. Fluorimetry measurements indicated that KCNQ1-KCNE1 channel S4 movement was 30-fold slower than that of the well-studied Drosophila Shaker Kv channel.
A study investigated how KCNE1 affects KCNQ1 activation, finding it slows down KCNQ1's activity significantly. This slowing is so profound that the charge flow associated with KCNQ1's movement (gating current) becomes undetectable.  The researchers used fluorimetry to track S4 movement in KCNQ1 and found that KCNE1 slowed this movement 30 times more than a similar study on the Shaker Kv channel from Drosophila.