Functional modulation of the ATP-sensitive potassium channel by extracellular signal-regulated kinase-mediated phosphorylation

Abstract

ATP-sensitive potassium (Katp) channels play an important role in controlling insulin secretion and vascular tone as well as protecting neurons under metabolic stress. We have previously demonstrated that stimulation of the Katp channel by nitric oxide (NO) requires activation of Ras- and extracellular signal-regulated kinase (ERK) of the mitogen-activated protein kinase (MAPK) family. However, the mechanistic link between ERK and the Katp channel remained unknown. To investigate how ERK modulates the function of Katp channels, we performed single-channel recordings in combination with site-directed mutagenesis. The Kir6.2/SUR1 channel, a neuronal Katp channel isoform, was expressed in human embryonic kidney (HEK) 293 cells by transient transfection. Direct application of the activated ERK2 to the cytoplasmic surface of excised, inside-out patches markedly enhanced the single-channel activity of Kir6.2/SUR1 channels. The normalized open probability (NPo) and opening frequency were significantly increased, whereas the mean closed duration was reduced. The single-channel conductance level was not affected. The ERK2-induced stimulation of Kir6.2/SUR1 channels was prevented by heat-inactivation of the enzyme. Furthermore, alanine substitutions of T341 and S385 to disrupt the potential ERK phosphorylation sites present in the Kir6.2 subunit significantly abrogated the stimulatory effects of ERK2, while aspartate substitutions of T341 and S385 to mimic the (negative) charge effect of phosphorylation rendered a small yet significant reduction in the ATP sensitivity of the channel. Taken together, here we report for the first time that ERK2/MAPK activates neuronal-type Katp channels, and this stimulation requires ERK phosphorylation of the Kir6.2 subunit at T341 and S385 residues. The ERK2-induced Katp channel stimulation can be accounted for by changes in channel gating that destabilize the closed states and by reduction in the ATP sensitivity. As Kir6.2 is the pore-forming subunit of Katp channels, ERK2-mediated phosphorylation may represent a common mechanism for Katp channel regulation in different tissues.