Functional Knockout of the Transient Outward Current, Long-QT Syndrome, and Cardiac Remodeling in Mice Expressing a Dominant-Negative Kv4 α Subunit

Abstract —A novel in vivo experimental strategy, involving cell type–specific expression of a dominant-negative K + channel pore-forming α subunit, was developed and exploited to probe the molecular identity of the cardiac transient outward K + current ( I to ). A point mutation (W to F) was introduced at position 362 in the pore region of Kv4.2 to produce a nonconducting mutant (Kv4.2W362F) subunit. Coexpression of Kv4.2W362F with Kv4.2 (or Kv4.3) attenuates the wild-type currents, and the effect is subfamily specific; ie, Kv4.2W362F does not affect heterologously expressed Kv1.4 currents. With the use of the α-myosin heavy chain promoter to direct cardiac-specific expression, several lines of Kv4.2W362F transgenic mice were generated. Electrophysiological recordings reveal that I to is selectively eliminated in ventricular myocytes isolated from transgenic mice expressing Kv4.2W362F, thereby demonstrating directly that the Kv 4 subfamily underlies I to in the mammalian heart. Functional knockout of I to leads to marked increases in action potential durations in ventricular myocytes and to prolongation of the QT interval in surface ECG recordings. In addition, a novel rapidly activating and inactivating K + current, which is not detectable in myocytes from nontransgenic littermates, is evident in Kv4.2W362F-expressing ventricular cells. Importantly, these results demonstrate that electrical remodeling occurs in the heart when the expression of endogenous K + channels is altered.