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The aim of the present study was to assess differences in transient outward potassium current (Ito) between the right ventricular free wall and the interventricular septum of the adult rat ventricle and to evaluate the relative contributions of Kv4.2, Kv4.3, and Kv1.4 to Ito in these regions. The results show that Ito is composed of both rapidly and slowly recovering components in the right wall and septum. The fast component had a significantly higher density in the right free wall than in the septum, whereas the slow component did not differ between the two sites. Kv4.2 mRNA and protein levels were also highest in the right wall and correlated with Ito density, whereas Kv4.3 was expressed uniformly in these regions. The kinetics of the rapidly recovering component of Ito in myocytes was similar to that recorded in tsa-201 cells expressing Kv4.2 and Kv4.3 channels. Kv1.4 mRNA and protein expression correlated well with the density of the slowly recovering Ito, whereas the recovery kinetics of the slow component were identical to Kv1.4 expressed in tsa-201 cells. In conclusion, expression of Kv1.4, Kv4.2, and Kv4.3 differs between regions in rat hearts. Regionally specific differences in the genetic composition of Ito can account for the region-specific properties of this current.
Wickenden et al. (1999) studied this question.