Characterisation of Kv4.3 in HEK293 cells: comparison with the rat ventricular transient outward potassium current

Objective: The Shal (or Kv4) gene family has been proposed to be responsibl e for primary subunits of the transient outward potassium current (I-to). M ore precisely, Kv4.2 and Kv4.3 have been suggested to be the most likely mo lecular correlates for I-to in rat cells. The purpose of the present study was to compare the properties of the rat Kv4.3 gene product when expressed in a human cell line (HEK293 cells) with that of I-to recorded from rat ven tricular cells. Methods: The cDNA encoding the rat Kv4.3 potassium channel was cloned into the pHook2 mammalian expression vector and expressed into H EK293. Patch clamp experiments using the whole cell configuration were used to characterise the electrophysiological parameters of the current induced by Kv4.3 in comparison with the rat ventricular myocyte I-to current. Resu lts: The transfection of HEK293 cells with rat Kv4.3 resulted in the expres sion of a time- and voltage-dependent outward potassium current. The curren t activated for potentials positive to -40 mV and the steady-state inactiva tion curve had a midpoint of -47.4+/-0.3 mV and a slope of 5.9+/-0.2 mV. Ra t ventricular I-to current was activated at potentials positive to -20 mV a nd inactivated with a half-inactivation potential and a Boltzmann factor of -29.1+/-0.7 mV and 4.5+/-0.5 mV, respectively. The time course of recovery from inactivation of rat Kv4.3 expressed in HEK293 cells and of I-to recor ded from native rat ventricular cells were exponentials with time constants of 213.2+/-4.1 msec and 23.+/-1.5 msec, respectively. Pharmacologically, I -to of rat myocytes showed a greater sensitivity to 3-aminopyridine than Kv 4.3 since half-maximal effects were obtained with 1.54+/-0.13 mM and 0.14+/ -0.02 mM on Kv4.3 and I-to, respectively. In both Kv4.3 and I-to, 4-aminopy ridine appears to bind to the closed state of the channel. Finally, althoug h a higher level of expression was observed in the atria compared to the ve ntricle, the distribution of the Kv4.3 gene across the ventricles appeared to be homogenous. Conclusion: The results of the present study show that Kv 4.3 channel may play a major role in the molecular structure of the rat car diac I-to current. Furthermore, because the distribution of Kv4.3 across th e ventricle is homogenous, the blockade of this channel by specific drugs m ay not alter the normal heterogeneity of I-to current. (C) 1999 Elsevier Sc ience B.V. All rights reserved.