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Novel mechanism of HERG current suppression in LQT2: shift in voltage dependence of HERG inactivation.

T Nakajima, T Furukawa, T Tanaka, Y Katayama, R Nagai, Y Nakamura, M Hiraoka

Circ. Res., 1998 Aug 24 , 83, 415-22

In a Xenopus oocyte heterologous expression system, we characterized the electrophysiology of 3 novel missense mutations of HERG identified in Japanese LQT2 families: T474I (within the S2-S3 linker), A614V, and V630L (in the outer mouth of pore-forming region). For each of the 3 mutations, injection of mutant cRNA alone did not express detectable currents. Coinjection of wild-type (WT) along with each mutant cRNA (T474I/WT, A614V/WT, and V630L/WT) suppressed HERG current in a dominant-negative manner, and the order of magnitude of current suppression was V630L/WT>A614V/WT>T474I/WT. In addition to decreases in slope conductance for all 3 mutants, the voltage dependence of steady-state inactivation was shifted to negative potentials for V630L/WT and A614V/WT. Consequently, channel availability at positive potentials was diminished, and inward rectification was enhanced for these 2 mutants. Thus, missense mutations of HERG caused dominant-negative suppression through multiple mechanisms. The shift in voltage dependence of HERG inactivation and the resulting enhanced inward rectification in A614V/WT and V630L/WT provide a novel mechanism for suppression of the HERG current carrying outward current during the repolarization phase of the action potential.