ATP sensitivity of the ATP-sensitive K⁺ channel in intact and permeabilized pancreatic β-cells

ATP-sensitive K⁺ channels (K_ATP channels) couple cell metabolism to electrical activity and thereby to physiological processes such as hormone secretion, muscle contraction, and neuronal activity. However, the mechanism by which metabolism regulates K_ATP channel activity, and the channel sensitivity to inhibition by ATP in its native environment, remain controversial. Here, we used {alpha}-toxin to permeabilize single pancreatic β-cells and measure K_ATP channel ATP sensitivity. We show that the channel ATP sensitivity is approximately sevenfold lower in the permeabilized cell than in the inside-out patch and that this is caused by interaction of Mg-nucleotides with the nucleotide-binding domains of the SUR1 subunit of the channel. The ATP sensitivity observed in permeabilized cells accounts quantitatively for K_ATP channel activity in intact cells. Thus, our results show that the principal metabolic regulators of K _ATP channel activity are MgATP and MgADP.