Sensitivity of KATP channels to cellular metabolic disorders and the underlying structural basis

Aim: ATP-sensitive potassium (K-ATP) channels formed by a combination of SUR/Kir6.x subunits play a crucial role in protection against hypoxic or ischemic injuries resulting from cell metabolic disorders. In this study we investigated the effects of Na-azide, a metabolic inhibitor, on K-ATP channels expressed in Xenopus oocytes, and explored the structure basis for their sensitivity to cell metabolic disorders. Methods: Six subtypes of K-ATP channels (wild SUR1/Kir6.2, SUR2B/Kir6.2, SUR1/Kir6.1, SUR2B/Kir6.1, SUR2A/Kir6.2 and SUR2A/Kir6.1), as well as eleven subtypes of K-ATP channels with mutant subunits were expressed in Xenopus oocytes. K-ATP currents were recorded using a two-electrode voltage clamp recording technique. The drugs were applied through bath. Results: Except SUR2A/Kir6.1, five subtypes of K-ATP channels were activated by Na-azide (3 mmol/L) with an order of the responses: SUR1/Kir6.2>SUR2B/Kir6.2>SUR1/Kir6.1>SUR2B/Kir6.1>SUR2A/Kir6.2, and the opening rate (t(1/2)) was SUR1/Kir6.x>SUR2B/Kir6.x> SUR2A/Kir6.2. Furthermore, Kir6.2, rather than Kir6.1, had intrinsic sensitivity to Na-azide, and the residues involved in ATP-binding (R50 and K185) or pH-sensing (H175) were associated with the sensitivity of the Kir6.2 subunit to Na-azide. Moreover, the residues (K707 and K1348) within the Walker A (WA) motifs of two nucleotide-binding domains (NBDs) were essential for SUR2B/Kir6.x (especially SUR2B/ Kir6.1) channel activation by Na-azide, suggesting a key role for Mg-adenine nucleotide binding and/or hydrolysis in the SUR2B subunit. Conclusion: Among the six subtypes of K-ATP channels, SUR1/Kir6.2 is the most sensitive, whereas SUR2A/Kir6.1 is insensitive, to cell metabolic disorders. The Kir6.2 subunit, rather than the Kir6.1 subunit, has intrinsic sensitivity to cell metabolic disorders. The residues (K707 and K1348) within the WA motifs of SUR2B are important for the sensitivity of SUR2B/Kir6.x channels to cell metabolic disorders.