Metabolic regulation of the pancreatic β-cell ATP-sensitive K ⁺ channel: A pas de deux

Closure of ATP-sensitive K⁺ channels (K_ATP channels) is a key step in glucose-stimulated insulin secretion. The precise mechanism(s) by which glucose metabolism regulates K_ATP channel activity, however, remains controversial. It is widely believed that the principal determinants are the intracellular concentrations of the metabolic ligands, ATP and ADP, which have opposing actions on K_ATP channels, with ATP closing and MgADP opening the channel. However, the sensitivity of the channel to these nucleotides in the intact cell, and their relative contribution to the regulation of channel activity, remains unclear. The precise role of phosphoinositides and long-chain acyl-CoA esters, which are capable of modulating the channel ATP sensitivity, is also uncertain. Furthermore, it is still a matter of debate whether it is changes in the concentration of ATP, of MgADP, or of other agents, which couples glucose metabolism to K_ATP channel activity. In this article, we review current knowledge of the metabolic regulation of the K_ATP channel and provide evidence that MgADP (or MgATP hydrolysis), acting at the regulatory subunit of the channel, shifts the ATP concentration-response curve into a range in which the channel pore can respond to dynamic changes in cytosolic ATP. This metabolic pas de deux orchestrates the pivotal role of ATP in metabolic regulation of the K _ATP channel.