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Rescue of ion channel function in deafness-causing KCNQ4 mutants by synthetic channel openers.
M G Leitner, A Feuer, O Ebers, D N Schreiber, C R Halaszovich, D Oliver, Michael G Leitner, Anja Feuer, Olga Ebers, Daniela N Schreiber, Christian R Halaszovich, Dominik Oliver
Background and Purpose: DFNA2 is a frequent hereditary hearing disorder caused by loss-of-function mutations in the voltage-gated potassium channel KCNQ4 (Kv7.4). KCNQ4 mediates the predominant K(+) conductance, I(K,n) , of auditory outer hair cells (OHCs), and loss of KCNQ4 function leads to degeneration of OHCs resulting in progressive hearing loss. Here we explore the possibility to recover channel activity of mutant KCNQ4 by synthetic KCNQ channel openers. Experimental Approach: Whole cell patch clamp recordings were performed on Chinese hamster ovary (CHO) cells transiently expressing KCNQ4 wild-type (wt) and DFNA2-relevant mutants, and from acutely isolated OHCs. Key Results: Various known KCNQ channel openers robustly enhanced KCNQ4 currents. The strongest potentiation was observed with a combination of zinc pyrithione plus retigabine (ZnP/Ret). A similar albeit less pronounced current enhancement was observed with native I(K,n) currents in rat OHCs. DFNA2 mutations located in the channel's pore region abolished channel function and these mutant channels were completely irresponsive to channel openers. However, function of a DFNA2 mutation located in the proximal C-terminus was rescued by combined application of both openers. Co-expression of wt and KCNQ4 pore mutants suppressed currents to barely detectable levels. In this dominant-negative situation, channel openers essentially restored currents back to wt levels. This rescue most likely occurred through strong activation of the small fraction of homomeric wild-type channels only. Conclusions and Implications: Our data suggest that by stabilizing the KCNQ4-mediated conductance in OHCs, chemical channel openers may protect from OHC degeneration and progression of hearing loss in DFNA2.