Human Slack Potassium Channel Mutations Increase Positive Cooperativity between Individual Channels

• Slack KCNT1 mutations are found in three different epilepsy syndromes
• Abnormal interactions between individual mutants greatly increase K+ current
• Cooperativity enhances K+ current even in a mutant with reduced channel conductance
• The same mutation can produce different forms of epilepsy in different individuals

SummaryDisease-causing mutations in ion channels generally alter intrinsic gating properties such as activation, inactivation, and voltage dependence. We examined nine different mutations of the KCNT1 (Slack) Na+-activated K+ channel that give rise to three distinct forms of epilepsy. All produced many-fold increases in current amplitude compared to the wild-type channel. This could not be accounted for by increases in the intrinsic open probability of individual channels. Rather, greatly increased opening was a consequence of cooperative interactions between multiple channels in a patch. The degree of cooperative gating was much greater for all of the mutant channels than for the wild-type channel, and could explain increases in current even in a mutant with reduced unitary conductance. We also found that the same mutation gave rise to different forms of epilepsy in different individuals. Our findings indicate that a major consequence of these mutations is to alter channel-channel interactions.

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