Attenuation of the Slow Component of Delayed Rectification, Action Potential Prolongation, and Triggered Activity in Mice Expressing a Dominant-Negative Kv2 α Subunit

Abstract

Abstract —An in vivo experimental strategy, involving cardiac-specific expression of a mutant Kv 2.1 subunit that functions as a dominant negative, was exploited in studies focused on exploring the role of members of the Kv2 subfamily of pore-forming (α) subunits in the generation of functional voltage-gated K + channels in the mammalian heart. A mutant Kv2.1 α subunit (Kv2.1N216) was designed to produce a truncated protein containing the intracellular N terminus, the S1 membrane–spanning domain, and a portion of the S1/S2 loop. The truncated Kv2.1N216 was epitope tagged at the C terminus with the 8–amino acid FLAG peptide to generate Kv2.1N216FLAG. No ionic currents are detected on expression of Kv2.1N216FLAG in HEK-293 cells, although coexpression of this construct with wild-type Kv2.1 markedly reduced the amplitudes of Kv2.1-induced currents. Using the α-myosin heavy chain promoter to direct cardiac specific expression of the transgene, 2 lines of Kv2.1N216FLAG-expressing transgenic mice were generated. Electrophysiological recordings from ventricular myocytes isolated from these animals revealed that I K, slow is selectively reduced. The attenuation of I K, slow is accompanied by marked action potential prolongation, and, occasionally, spontaneous triggered activity (apparently induced by early afterdepolarizations) is observed. The time constant of inactivation of I K, slow in Kv2.1N216FLAG-expressing cells (mean±SEM=830±103 ms; n=17) is accelerated compared with the time constant of I K, slow inactivation (mean±SEM=1147±57 ms; n=25) in nontransgenic cells. In addition, unlike I K, slow in wild-type cells, the component of I K, slow remaining in the Kv2.1N216FLAG-expressing cells is insensitive to 25 mmol/L tetraethylammonium. Taken together, these observations suggest that there are 2 distinct components of I K, slow in mouse ventricular myocytes and that Kv2 α subunits underlie the more slowly inactivating, tetraethylammonium-sensitive component of I K, slow . In vivo telemetric recordings also reveal marked QT prolongation, consistent with a defect in ventricular repolarization, in Kv2.1N216FLAG-expressing transgenic mice.