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

An in vivo experimental strategy, involving cardiac-specific expression of a mutant Kv 2.1 subunit that functions as a dominant negative, was exploite d in studies focused on exploring the role of members of the Kv2 subfamily of pore-forming (alpha) subunits in the generation of functional voltage-ga ted K+ channels in the mammalian heart. A mutant Kv2.1 alpha subunit (Kv2.1 N216) was designed to produce a truncated protein containing the intracellu lar 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 th e 8-amino acid FLAG peptide to generate Kv2.1N216FLAG. No ionic currents ar e detected on expression of Kv2.1N216FLAG in HEK-293 cells, although coexpr ession of this construct with wild-type Kv2.1 markedly reduced the amplitud es of Kv2.1-induced currents. Using the alpha-myosin heavy chain promoter t o direct cardiac specific expression of the transgene, 2 lines of Kv2.1N216 FLAG-expressing transgenic mice were generated. Electrophysiological record ings from ventricular myocytes isolated from these animals revealed that I- K,I-slow is selectively reduced. The attenuation of I-K,I-slow is accompani ed by marked action potential prolongation, and, occasionally, spontaneous triggered activity (apparently induced by early afterdepolarizations) is ob served. The time constant of inactivation of I-K,I-slow in Kv2.1N216FLAG-ex pressing cells (mean +/- SEM = 830 +/- 103 ms; n = 17) is accelerated compa red 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 i n wild-type cells, the component of I-K,I-slow remaining in the Kv2.1N216FL AG-expressing cells is insensitive to 25 mmol/L tetraethylammonium. Taken t ogether, these observations suggest that there are 2 distinct components of I-K,I-slow in mouse ventricular myocytes and that Kv2 alpha subunits under lie the more slowly inactivating, tetraethylammonium-sensitive component of I-K,I-slow. In vivo telemetric recordings also reveal marked QT prolongati on, consistent with a defect in ventricular repolarization, in Kv2.1N216FLA G-expressing transgenic mice.