Key result
Expression of the RK5 (rat Kv4.2) channel in Xenopus oocytes revealed rapid activation and inactivation kinetics and sensitivity to 4-AP (IC50 = 5 mM), suggesting it contributes to the cardiac Ito current.
The functional characteristics of the RK5 voltage-gated K+ channel suggest it contributes to the transient outward current (Ito) in the heart.
Supports Kv4.2 as Ito candidate in rodents; leaves open human relevance and therapeutic implications.
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.
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Blair et al. (1991) studied Basic science (voltage-gated K+ channel). RK5 (rat Kv4.2) expression in Xenopus oocytes was evaluated on Electrophysiological and pharmacological properties. Expression of the RK5 (rat Kv4.2) channel in Xenopus oocytes revealed rapid activation and inactivation kinetics and sensitivity to 4-AP (IC50 = 5 mM), suggesting it contributes to the cardiac Ito current.
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