Molecular Determinants of Cardiac KATP Channel Activation by Epoxyeicosatrienoic Acids

Hon-Chi Lee,Tong Lu,Min-Pyo Hong

doi:10.1074/jbc.m414065200

Abstract

We have previously reported that epoxyeicosatrienoic acids (EETs), the cytochrome P450 epoxygenase metabolites of arachidonic acid, are potent stereospecific activators of the cardiac K(ATP) channel. The epoxide group in EET is critical for reducing channel sensitivity to ATP, thereby activating the channel. This study is to identify the molecular sites on the K(ATP) channels for EET-mediated activation. We investigated the effects of EETs on Kir6.2delta C26 with or without the coexpression of SUR2A and on Kir6.2 mutants of positively charged residues known to affect channel activity coexpressed with SUR2A in HEK293 cells. The ATP IC50 values were significantly increased in Kir6.2 R27A, R50A, K185A, and R201A but not in R16A, K47A, R54A, K67A, R192A, R195A, K207A, K222A, and R314A mutants. Similar to native cardiac K(ATP) channel, 5 microM 11,12-EET increased the ATP IC50 by 9.6-fold in Kir6.2/SUR2A wild type and 8.4-fold in Kir6.2delta C26. 8,9- and 14,15-EET regioisomers activated the Kir6.2 channel as potently as 11,12-EET. 8,9- and 11,12-EET failed to change the ATP sensitivity of Kir6.2 K185A, R195A, and R201A, whereas their effects were intact in the other mutants. 14,15-EET had a similar effect with K185A and R201A mutants, but instead of R195A, it failed to activate Kir6.2R192A. These results indicate that activation of Kir6.2 by EETs does not require the SUR2A subunit, and the region in the Kir6.2 C terminus from Lys-185 to Arg-201 plays a critical role in EET-mediated Kir6.2 channel activation. Based on computer modeling of the Kir6.2 structure, we infer that the EET-Kir6.2 interaction may allosterically change the ATP binding site on Kir6.2, reducing the channel sensitivity to ATP.

Highlights

Physiological conditions remains unclear, it is crucial in ischemic preconditioning, and activation of KATP channels occurs during cardiac ischemia and hypoxia, leading to reduced Ca2ϩ influx and intracellular Ca2ϩ overload [2]
Single channel recordings confirmed that the effects of ATP concentrations on channel Po were reduced in the presence of 5 ␮M 11,12-epoxyeicosatrienoic acids (EETs) (Fig. 2B). 5 ␮M 11,12-EET increased the ATP IC50 of the channel from a base line of 44.4 Ϯ 16.4 to 468.4 Ϯ 135.0 ␮M (n ϭ 6, p Ͻ 0.05 versus base line (Fig. 2C)
The Hill coefficient (H) remained unchanged (1.23 Ϯ 0.08 at base line versus 1.28 Ϯ 0.10 with EET; n ϭ 6, p ϭ not significant). These results suggest that the Kir6.2 wt channels expressed in HEK293 cells retain the sensitivity to activation by EET, similar to native KATP channels in cardiac ventricular myocytes

Summary

Introduction

Physiological conditions remains unclear, it is crucial in ischemic preconditioning, and activation of KATP channels occurs during cardiac ischemia and hypoxia, leading to reduced Ca2ϩ influx and intracellular Ca2ϩ overload [2]. We have previously reported that EETs are potent activators of the cardiac KATP channels, reducing the channel sensitivity to ATP, and had an EC50 of about 30 nM [17, 18].

Results

Conclusion