Role of heteromultimers in the generation of myocardial transient outward K+ currents

Previous studies have demonstrated a role for Kv4 alpha subunits in the generation of the fast transient outward K+ current, I-to,I-f, in the mammalian myocardium. The experiments here were undertaken to explore the role of homomeric/heteromeric assembly of Kv4.2 and Kv4.3 and of the Kv channel accessory subunit, KChIP(2), in the generation of mouse ventricular I-to,I-f. Western blots reveal that the expression of Kv4.2 parallels the regional heterogeneity in I-to,I-f density, whereas Kv4.3 and KChIP2 are uniformly expressed in adult mouse ventricles. Antisense oligodeoxynucleotides (AsODNs) targeted against Kv4.21 or Kv4.3 selectively attenuate I-to,I-f in mouse ventricular cells. Adenoviral-mediated coexpression of Kv4.2 and Kv4.3 in HEK-293 cells and in mouse ventricular myocytes produces transient outward K+ currents with properties distinct from those produced on expression of Kv4.2 or Kv4.3 alone, and the gating properties of the heteromeric Kv4.2/Kv4.3 channels in ventricular cells are more similar to native I-to,I-f than are the homomeric Kv4.2 or Kv4.3 channels. Biochemical studies reveal that Kv4.2, Kv4.3, and KChIP2 coimmuno-precipitate from adult mouse ventricles. In addition, most of the Kv4.21 and KChIP2 are associated with Kv4.3 in situ. Taken together, these results demonstrate that functional mouse ventricular I-to,I-f, channels are heteromeric, comprising Kv4.2/Kv4.3 a subunits and KChIP2. The results here also suggest that Kv4.2 is the primary determinant of the regional heterogeneity in I-to,I-f, expression in adult mouse ventricle.