Attenuation of the slow component of delayed rectification, action potential prolongation, and triggered activity in mice expressing a dominant-negative Kv2 α subunit

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 (alpha) subunits in the generation of functional voltage-gated K+ channels in the mammalian heart. A mutant Kv2.1 alpha 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 alpha-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,I-slow is selectively reduced. The attenuation of I-K,I-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,I-slow in Kv2.1N216FLAG-expressing cells (mean +/- SEM = 830 +/- 103 ms; n = 17) is accelerated compared with the time constant of I-K,I-slow inactivation (mean +/- SEM = 1147 +/- 57 ms; n = 25) in nontransgenic cells. In addition, unlike I-K,I-slow in wild-type cells, the component of I-K,I-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,I-slow in mouse ventricular myocytes and that Kv2 alpha subunits underlie the more slowly inactivating, tetraethylammonium-sensitive component of I-K,I-slow. In vivo telemetric recordings also reveal marked QT prolongation, consistent with a defect in ventricular repolarization, in Kv2.1N216FLAG-expressing transgenic mice.