Functional characterization of RK5, a voltage-gated K+ channel cloned from the rat cardiovascular system

A voltage-sensitive K+ channel previously cloned from rat heart designated RK5 (rat Kv4.2) (Roberds and Tamkun, 1991, Proc. Natl. Acad. Sci. USA 88, 1798-1802) was functionally characterized in the Xenopus oocyte expression system. RK5 is a homolog of the Drosophila Shal K+ channel, activates with a rise time of 2.8 ms, has a midpoint for activation of -1 mV and rapidly inactivates with time constants of 15 and 60 ms. RK5 is sensitive to 4-AP, IC50 = 5 mM, and is insensitive to TEA and dendrotoxins. The voltage dependence and kinetics of the RK5 induced currents suggest this channel contributes to the Ito current in heart.