Mutations in the KCNT1 (Slack, KNa1.1) sodium-activated potassium channel produce severe epileptic encephalopathies. Expression in heterologous systems has shown that the disease-causing mutations give rise to channels that have increased current amplitude. It is not known, however, whether such gain of function occurs in human neurons, nor whether such increased KNa current is expected to suppress or increase the excitability of cortical neurons. Using genetically engineered human induced pluripotent stem cell (iPSC)-derived neurons, we have now found that sodium-dependent potassium currents are increased several-fold in neurons bearing a homozygous P924L mutation. In current-clamp recordings, the increased KNa current in neurons with the P924L mutation acts to shorten the duration of action potentials and to increase the amplitude of the afterhyperpolarization that follows each action potential. Strikingly, the number of action potentials that were evoked by depolarizing currents as well as maximal firing rates were increased in neurons expressing the mutant channel. In networks of spontaneously active neurons, the mean firing rate, the occurrence of rapid bursts of action potentials, and the intensity of firing during the burst were all increased in neurons with the P924L Slack mutation. The feasibility of an increased KNa current to increase firing rates independent of any compensatory changes was validated by numerical simulations. Our findings indicate that gain-of-function in Slack KNa channels causes hyperexcitability in both isolated neurons and in neural networks and occurs by a cell-autonomous mechanism that does not require network interactions.
Bibliographical noteFunding Information:
This work was supported by National Institutes of Health NS102239 to L.K.K. and a Swebilius Foundation Grant to I.H.Q. K.P.M., M.J.M., and E.M.J. are employed by FUJIFILM Cellular Dynamics, Inc. The remaining authors declare no competing financial interests.
Received June 28, 2018; revised July 8, 2019; accepted July 17, 2019. Authorcontributions:I.H.Q.,K.P.M.,F.H.G.,andL.K.K.designedresearch;I.H.Q.,S.S.,K.P.M.,Y.Z.,S.R.A.,M.R.M., M.C.M., and L.K.K. performed research; I.H.Q., S.S., K.P.M., Y.Z., S.R.A., M.R.M., M.C.M., and L.K.K. analyzed data; I.H.Q. wrote the first draft of the paper; I.H.Q., S.S., K.P.M., Y.Z., S.R.A., M.J.M., and L.K.K. edited the paper; K.P.M., M.J.M., and E.M.J. contributed unpublished reagents/analytic tools. Acknowledgements: This work was supported by National Institutes of Health NS102239 to L.K.K. and a Swebi-lius Foundation Grant to I.H.Q. K.P.M., M.J.M., and E.M.J. are employed by FUJIFILM Cellular Dynamics, Inc. The remaining authors declare no competing financial interests. *I.H.Q., S.S., and K.P.M. contributed equally to the work Correspondence should be addressed to Leonard K. Kaczmarek at firstname.lastname@example.org.
Copyright © 2019 the authors
- Action potential
- Epileptic encephalopathy
- Potassium channels
ASJC Scopus subject areas
- Neuroscience (all)