A sensitive regulator of cellular potassium: A class of potassium channels called K2P channels modulates resting membrane potential in most cells. The channels are regulated by multiple ligands, including the antidepressant drug Prozac, as well as factors such as mechanical stretch and voltage. Dong et al. determined the structure of the human K2P channel, TREK-2, in two conformations and bound to a metabolite of Prozac. The structures show how ligand binding or mechanical stretch might induce switching between the states. Although both states have open channels, one appears primed for gating. A Prozac metabolite binds to the primed state and prevents conformational switching. K2P channels are not a target of Prozac, but their inhibition may contribute to side effects. Science , this issue p. 1256

The ATP‐sensitive K‐channel (K‐ATP channel) plays a key role in insulin secretion from pancreatic β‐cells. It is closed by glucose metabolism, which stimulates insulin secretion, and opened by the drug diazoxide, which inhibits insulin release. Metabolic regulation is mediated by changes in ATP and Mg‐ADP, which inhibit and potentiate channel activity, respectively. The β‐cell K‐ATP channel consists of a pore‐forming subunit, Kir6.2, and a regulatory subunit, SUR1. We have mutated (independently or together) two lysine residues in the Walker A (WA) motifs of the first (K719A) and second (K1384M) nucleotide‐binding domains (NBDs) of SUR1. These mutations are expected to inhibit nucleotide hydrolysis. Our results indicate that the WA lysine of NBD1 (but not NBD2) is essential for activation of K‐ATP currents by diazoxide. The potentiatory effects of Mg‐ADP required the presence of the WA lysines in both NBDs. Mutant currents were slightly more sensitive to ATP than wild‐type currents. Metabolic inhibition led to activation of wild‐type and K1384M currents, but not K719A or K719A/K1384M currents, suggesting that there may be a factor in addition to ATP and ADP which regulates K‐ATP channel activity.

Biological ion channels are nanoscale transmembrane pores. When water and ions are enclosed within the narrow confines of a sub-nanometer hydrophobic pore, they exhibit behavior not evident from macroscopic descriptions. At this nanoscopic level, the unfavorable interaction between the lining of a hydrophobic pore and water may lead to stochastic liquid-vapor transitions. These transient vapor states are "dewetted", i.e. effectively devoid of water molecules within all or part of the pore, thus leading to an energetic barrier to ion conduction. This process, termed "hydrophobic gating", was first observed in molecular dynamics simulations of model nanopores, where the principles underlying hydrophobic gating (i.e., changes in diameter, polarity, or transmembrane voltage) have now been extensively validated. Computational, structural, and functional studies now indicate that biological ion channels may also exploit hydrophobic gating to regulate ion flow within their pores. Here we review the evidence for this process and propose that this unusual behavior of water represents an increasingly important element in understanding the relationship between ion channel structure and function.

There has been considerable debate as to whether adenosine triphosphate (ATP) is compartmentalized within cells and, in particular, whether the ATP concentration directly beneath the plasma membrane, experienced by membrane proteins, is the same as that of the bulk cytoplasm. This issue has been difficult to address because there is no indicator of cytosolic ATP, such as those available for Ca²⁺, capable of resolving the submembrane ATP concentration ([ATP]_sm) in real time within a single cell. We show here that mutant ATP-sensitive K⁺ channels can be used to measure [ATP]_sm by comparing the increase in current amplitude on patch excision with the ATP dose-response curve. In Xenopus oocytes, [ATP]_sm was 4.6 ± 0.3 mm (n = 29) under resting conditions, slightly higher than that measured for the bulk cytoplasm (2.3 mm). In mammalian (COSm6) cells, [ATP]_smwas slightly lower and averaged 1.4 ± 0.1 mm(n = 66). Metabolic poisoning (10 min of 3 mm azide) produced a significant fall in [ATP]_sm in both types of cells: to 1.2 ± 0.1 mm (n = 24) in oocytes and 0.8 ± 0.11 mm for COSm6 cells. We conclude that [ATP]_sm lies in the low millimolar range and that there is no gradient between bulk cytosolic and submembrane [ATP].