Loss of ATP-Sensitive Potassium Channel Surface Expression in Heart Failure Underlies Dysregulation of Action Potential Duration and Myocardial Vulnerability to Injury

The search for new approaches to treatment and prevention of heart failure is a major challenge in medicine. The adenosine triphosphate-sensitive potassium (K_ATP) channel has been long associated with the ability to preserve myocardial function and viability under stress. High surface expression of membrane K_ATP channels ensures a rapid energy-sparing reduction in action potential duration (APD) in response to metabolic challenges, while cellular signaling that reduces surface K_ATP channel expression blunts APD shortening, thus sacrificing energetic efficiency in exchange for greater cellular calcium entry and increased contractile force. In healthy hearts, calcium/calmodulin-dependent protein kinase II (CaMKII) phosphorylates the Kir6.2 K_ATP channel subunit initiating a cascade responsible for K_ATP channel endocytosis. Here, activation of CaMKII in a transaortic banding (TAB) model of heart failure is coupled with a 35–40% reduction in surface expression of K_ATP channels compared to hearts from sham-operated mice. Linkage between K_ATP channel expression and CaMKII is verified in isolated cardiomyocytes in which activation of CaMKII results in downregulation of K_ATP channel current. Accordingly, shortening of monophasic APD is slowed in response to hypoxia or heart rate acceleration in failing compared to non-failing hearts, a phenomenon previously shown to result in significant increases in oxygen consumption. Even in the absence of coronary artery disease, failing myocardium can be further injured by ischemia due to a mismatch between metabolic supply and demand. Ischemia-reperfusion injury, following ischemic preconditioning, is diminished in hearts with CaMKII inhibition compared to wild-type hearts and this advantage is largely eliminated when myocardial K_ATP channel expression is absent, supporting that the myocardial protective benefit of CaMKII inhibition in heart failure may be substantially mediated by K_ATP channels. Recognition of CaMKII-dependent downregulation of K_ATP channel expression as a mechanism for vulnerability to injury in failing hearts points to strategies targeting this interaction for potential preventives or treatments.     

ATP-sensitive potassium channels are altered in ventricular myocytes from diabetic rats

Hypoxia-induced shortening of the action potential duration, attributed to activation of the ATP-sensitive potassium (K_ATP) channels, occurs to a much greater extent in ventricular cells from diabetic rats. This study examined whether the K_ATP channels are altered in streptozotocin-diabetic myocardium. In inside-out patches from ventricular myocytes (with symmetrical 140 mM [K+]), inward K_ATP currents (at potentials negative to the K+ reversal potential) were similar in amplitude in control and diabetic patches (slope conductances: 69 and 74 pS, respectively). However, outward single-channel currents were larger for channels from diabetic heart cells than from control cells (e.g., at +75 mV the diabetic channel currents were 3.7 ± 0.3 pA vs. 2.7 ± 0.1 pA for control currents, p < 0.05), due to reduced inward rectification of diabetic channel currents. There was no difference in open and closed times between control and diabetic channels. The IC₅₀ for ATP inhibition of the K_ATP channel single-channel currents was 11.4 M for control currents and 4.7 M for diabetic channel currents. Thus, the major difference found between K_ATP channels from control and diabetic hearts was the greater outward diabetic single-channel current, which may contribute to the enhanced sensitivity to hypoxia (or ischemia) in diabetic hearts.     

Modeling Cardiac Action Potential Shortening Driven by Oxidative Stress-Induced Mitochondrial Oscillations in Guinea Pig Cardiomyocytes

Ischemia-induced shortening of the cardiac action potential and its heterogeneous recovery upon reperfusion are thought to set the stage for reentrant arrhythmias and sudden cardiac death. We have recently reported that the collapse of mitochondrial membrane potential (ΔΨ_m) through a mechanism triggered by reactive oxygen species (ROS), coupled to the opening of sarcolemmal ATP-sensitive potassium (K_ATP) channels, contributes to electrical dysfunction during ischemia-reperfusion. Here we present a computational model of excitation-contraction coupling linked to mitochondrial bioenergetics that incorporates mitochondrial ROS-induced ROS release with coupling between the mitochondrial energy state and electrical excitability mediated by the sarcolemmal K_ATP current (I_K,ATP). Whole-cell model simulations demonstrate that increasing the fraction of oxygen diverted from the respiratory chain to ROS production triggers limit-cycle oscillations of ΔΨ_m, redox potential, and mitochondrial respiration through the activation of a ROS-sensitive inner membrane anion channel. The periods of transient mitochondrial uncoupling decrease the cytosolic ATP/ADP ratio and activate I_K,ATP, consequently shortening the cellular action potential duration and ultimately suppressing electrical excitability. The model simulates emergent behavior observed in cardiomyocytes subjected to metabolic stress and provides a new tool for examining how alterations in mitochondrial oxidative phosphorylation will impact the electrophysiological, contractile, and Ca²⁺ handling properties of the cardiac cell. Moreover, the model is an important step toward building multiscale models that will permit investigation of the role of spatiotemporal heterogeneity of mitochondrial metabolism in the mechanisms of arrhythmogenesis and contractile dysfunction in cardiac muscle.     

K<Subscript>ATP</Subscript> channel polymorphism is associated with left ventricular size in hypertensive individuals: a large-scale community-based study

ATP-sensitive K⁺ (K_ATP) channel mutations have been identified in individuals with dilated cardiomyopathy and overt heart failure. Here, a common E23K functional polymorphism in the Kir6.2 channel pore versus cardiac phenotype was studied in a cross-sectional community-based cohort (n = 2,031). The KK genotype was associated with greater left ventricular size among subjects with increased stress load due to hypertension. These findings implicate Kir6.2 K23 as a risk factor for adverse subclinical myocardial remodeling, and underscore the significance of cardiac K_ATP channels within the population.     

Ligand-insensitive State of Cardiac ATP-sensitive K+ Channels : Basis for Channel Opening

The mechanism by which ATP-sensitive K⁺ (K_ATP) channels open in the presence of inhibitory concentrations of ATP remains unknown. Herein, using a four-state kinetic model, we found that the nucleotide diphosphate UDP directed cardiac K_ATP channels to operate within intraburst transitions. These transitions are not targeted by ATP, nor the structurally unrelated sulfonylurea glyburide, which inhibit channel opening by acting on interburst transitions. Therefore, the channel remained insensitive to ATP and glyburide in the presence of UDP. “Rundown” of channel activity decreased the efficacy with which UDP could direct and maintain the channel to operate within intraburst transitions. Under this condition, the channel was sensitive to inhibition by ATP and glyburide despite the presence of UDP. This behavior of the K_ATP channel could be accounted for by an allosteric model of ligand-channel interaction. Thus, the response of cardiac K_ATP channels towards inhibitory ligands is determined by the relative lifetime the channel spends in a ligand-sensitive versus -insensitive state. Interconversion between these two conformational states represents a novel basis for K_ATP channel opening in the presence of inhibitory concentrations of ATP in a cardiac cell.     

Heterogeneity of ATP-sensitive K+ Channels in Cardiac Myocytes: ENRICHMENT AT THE INTERCALATED DISK*

Ventricular ATP-sensitive potassium (K_ATP) channels link intracellular energy metabolism to membrane excitability and contractility. Our recent proteomics experiments identified plakoglobin and plakophilin-2 (PKP2) as putative K_ATP channel-associated proteins. We investigated whether the association of K_ATP channel subunits with junctional proteins translates to heterogeneous subcellular distribution within a cardiac myocyte. Co-immunoprecipitation experiments confirmed physical interaction between K_ATP channels and PKP2 and plakoglobin in rat heart. Immunolocalization experiments demonstrated that K_ATP channel subunits (Kir6.2 and SUR2A) are expressed at a higher density at the intercalated disk in mouse and rat hearts, where they co-localized with PKP2 and plakoglobin. Super-resolution microscopy demonstrate that K_ATP channels are clustered within nanometer distances from junctional proteins. The local K_ATP channel density, recorded in excised inside-out patches, was larger at the cell end when compared with local currents recorded from the cell center. The K_ATP channel unitary conductance, block by MgATP and activation by MgADP, did not differ between these two locations. Whole cell K_ATP channel current density (activated by metabolic inhibition) was ∼40% smaller in myocytes from mice haploinsufficient for PKP2. Experiments with excised patches demonstrated that the regional heterogeneity of K_ATP channels was absent in the PKP2 deficient mice, but the K_ATP channel unitary conductance and nucleotide sensitivities remained unaltered. Our data demonstrate heterogeneity of K_ATP channel distribution within a cardiac myocyte. The higher K_ATP channel density at the intercalated disk implies a possible role at the intercellular junctions during cardiac ischemia.     

Exercise responsive genes measured in peripheral blood of women with Chronic Fatigue Syndrome and matched control subjects

Background

Electrophysiological data suggest that cardiac K_ATP channels consist of Kir6.2 and SUR2A subunits, but the distribution of these (and other K_ATP channel subunits) is poorly defined. We examined the localization of each of the K_ATP channel subunits in the mouse and rat heart.

Results

Immunohistochemistry of cardiac cryosections demonstrate Kir6.1 protein to be expressed in ventricular myocytes, as well as in the smooth muscle and endothelial cells of coronary resistance vessels. Endothelial capillaries also stained positive for Kir6.1 protein. Kir6.2 protein expression was found predominantly in ventricular myocytes and also in endothelial cells, but not in smooth muscle cells. SUR1 subunits are strongly expressed at the sarcolemmal surface of ventricular myocytes (but not in the coronary vasculature), whereas SUR2 protein was found to be localized predominantly in cardiac myocytes and coronary vessels (mostly in smaller vessels). Immunocytochemistry of isolated ventricular myocytes shows co-localization of Kir6.2 and SUR2 proteins in a striated sarcomeric pattern, suggesting t-tubular expression of these proteins. Both Kir6.1 and SUR1 subunits were found to express strongly at the sarcolemma. The role(s) of these subunits in cardiomyocytes remain to be defined and may require a reassessment of the molecular nature of ventricular K_ATP channels.

Conclusions

Collectively, our data demonstrate unique cellular and subcellular K_ATP channel subunit expression patterns in the heart. These results suggest distinct roles for K_ATP channel subunits in diverse cardiac structures.     

Ankyrin-B Regulates Kir6.2 Membrane Expression and Function in Heart

Ankyrin polypeptides are critical for normal membrane protein expression in diverse cell types, including neurons, myocytes, epithelia, and erythrocytes. Ankyrin dysfunction results in defects in membrane expression of ankyrin-binding partners (including ion channels, transporters, and cell adhesion molecules), resulting in aberrant cellular function and disease. Here, we identify a new role for ankyrin-B in cardiac cell biology. We demonstrate that cardiac sarcolemmal K_ATP channels directly associate with ankyrin-B in heart via the K_ATP channel α-subunit Kir6.2. We demonstrate that primary myocytes lacking ankyrin-B display defects in Kir6.2 protein expression, membrane expression, and function. Moreover, we demonstrate a secondary role for ankyrin-B in regulating K_ATP channel gating. Finally, we demonstrate that ankyrin-B forms a membrane complex with K_ATP channels and the cardiac Na/K-ATPase, a second key membrane transporter involved in the cardiac ischemia response. Collectively, our new findings define a new role for cardiac ankyrin polypeptides in regulation of ion channel membrane expression in heart.     

Diadenosine tetraphosphate-gating of recombinant pancreatic ATP-sensitive K(+) channels

Diadenosine tetraphosphate (Ap4A) has been recently discovered in the pancreatic cells where targets ATP-sensitive K⁺ (K_ATP) channels, depolarizes the cell membrane and induces insulin secretion. However, whether Ap4A inhibit pancreatic K_ATP channels by targeting protein channel complex itself was unknown. Therefore, we coexpressed pancreatic KATP channel subunits, Kir6.2 and SUR1, in COS-7 cells and examined the effect of Ap4A on the single channel behavior using the inside-out configuration of the patch-clamp technique. Ap4A inhibited channel opening in a concentration-dependent manner. Analysis of single channels demonstrated that Ap4A did not change intraburst kinetic behavior of K_ATP channels, but rather decreased burst duration and increased between-burst duration. It is concluded that Ap4A antagonizes K_ATP channel opening by targeting channel subunits themselves and by keeping channels longer in closed interburst states.     

Activation of cGMP-dependent protein kinase stimulates cardiac ATP-sensitive potassium channels via a ROS/calmodulin/CaMKII signaling cascade

Background

Cyclic GMP (cGMP)-dependent protein kinase (PKG) is recognized as an important signaling component in diverse cell types. PKG may influence the function of cardiac ATP-sensitive potassium (K_ATP) channels, an ion channel critical for stress adaptation in the heart; however, the underlying mechanism remains largely unknown. The present study was designed to address this issue.

Methods and Findings

Single-channel recordings of cardiac K_ATP channels were performed in both cell-attached and inside-out patch configurations using transfected human embryonic kidney (HEK)293 cells and rabbit ventricular cardiomyocytes. We found that Kir6.2/SUR2A (the cardiac-type K_ATP) channels were activated by cGMP-selective phosphodiesterase inhibitor zaprinast in a concentration-dependent manner in cell-attached patches obtained from HEK293 cells, an effect mimicked by the membrane-permeable cGMP analog 8-bromo-cGMP whereas abolished by selective PKG inhibitors. Intriguingly, direct application of PKG moderately reduced rather than augmented Kir6.2/SUR2A single-channel currents in excised, inside-out patches. Moreover, PKG stimulation of Kir6.2/SUR2A channels in intact cells was abrogated by ROS/H₂O₂ scavenging, antagonism of calmodulin, and blockade of calcium/calmodulin-dependent protein kinase II (CaMKII), respectively. Exogenous H₂O₂ also concentration-dependently stimulated Kir6.2/SUR2A channels in intact cells, and its effect was prevented by inhibition of calmodulin or CaMKII. PKG stimulation of K_ATP channels was confirmed in intact ventricular cardiomyocytes, which was ROS- and CaMKII-dependent. Kinetically, PKG appeared to stimulate these channels by destabilizing the longest closed state while stabilizing the long open state and facilitating opening transitions.

Conclusion

The present study provides novel evidence that PKG exerts dual regulation of cardiac K_ATP channels, including marked stimulation resulting from intracellular signaling mediated by ROS (H₂O₂ in particular), calmodulin and CaMKII, alongside of moderate channel suppression likely mediated by direct PKG phosphorylation of the channel or some closely associated proteins. The novel cGMP/PKG/ROS/calmodulin/CaMKII signaling pathway may regulate cardiomyocyte excitability by opening K_ATP channels and contribute to cardiac protection against ischemia-reperfusion injury.     

KATP channels process nucleotide signals in muscle thermogenic response

Uniquely gated by intracellular adenine nucleotides, sarcolemmal ATP-sensitive K⁺ (K_ATP) channels have been typically assigned to protective cellular responses under severe energy insults. More recently, K_ATP channels have been instituted in the continuous control of muscle energy expenditure under non-stressed, physiological states. These advances raised the question of how K_ATP channels can process trends in cellular energetics within a milieu where each metabolic system is set to buffer nucleotide pools. Unveiling the mechanistic basis of the K_ATP channel-driven thermogenic response in muscles thus invites the concepts of intracellular compartmentalization of energy and proteins, along with nucleotide signaling over diffusion barriers. Furthermore, it requires gaining insight into the properties of reversibility of intrinsic ATPase activity associated with K_ATP channel complexes. Notwithstanding the operational paradigm, the homeostatic role of sarcolemmal K_ATP channels can be now broadened to a wider range of environmental cues affecting metabolic well-being. In this way, under conditions of energy deficit such as ischemic insult or adrenergic stress, the operation of K_ATP channel complexes would result in protective energy saving, safeguarding muscle performance and integrity. Under energy surplus, downregulation of K_ATP channel function may find potential implications in conditions of energy imbalance linked to obesity, cold intolerance and associated metabolic disorders.     

Sarcolemmal ATP-sensitive potassium channels modulate skeletal muscle function under low-intensity workloads

ATP-sensitive potassium (K_ATP) channels have the unique ability to adjust membrane excitability and functions in accordance with the metabolic status of the cell. Skeletal muscles are primary sites of activity-related energy consumption and have K_ATP channels expressed in very high density. Previously, we demonstrated that transgenic mice with skeletal muscle–specific disruption of K_ATP channel function consume more energy than wild-type littermates. However, how K_ATP channel activation modulates skeletal muscle resting and action potentials under physiological conditions, particularly low-intensity workloads, and how this can be translated to muscle energy expenditure are yet to be determined. Here, we developed a technique that allows evaluation of skeletal muscle excitability in situ, with minimal disruption of the physiological environment. Isometric twitching of the tibialis anterior muscle at 1 Hz was used as a model of low-intensity physical activity in mice with normal and genetically disrupted K_ATP channel function. This workload was sufficient to induce K_ATP channel opening, resulting in membrane hyperpolarization as well as reduction in action potential overshoot and duration. Loss of K_ATP channel function resulted in increased calcium release and aggravated activity-induced heat production. Thus, this study identifies low-intensity workload as a trigger for opening skeletal muscle K_ATP channels and establishes that this coupling is important for regulation of myocyte function and thermogenesis. These mechanisms may provide a foundation for novel strategies to combat metabolic derangements when energy conservation or dissipation is required.     

Regulation of Cardiac ATP-sensitive Potassium Channel Surface Expression by Calcium/Calmodulin-dependent Protein Kinase II

Cardiac ATP-sensitive potassium (K_ATP) channels are key sensors and effectors of the metabolic status of cardiomyocytes. Alteration in their expression impacts their effectiveness in maintaining cellular energy homeostasis and resistance to injury. We sought to determine how activation of calcium/calmodulin-dependent protein kinase II (CaMKII), a central regulator of calcium signaling, translates into reduced membrane expression and current capacity of cardiac K_ATP channels. We used real-time monitoring of K_ATP channel current density, immunohistochemistry, and biotinylation studies in isolated hearts and cardiomyocytes from wild-type and transgenic mice as well as HEK cells expressing wild-type and mutant K_ATP channel subunits to track the dynamics of K_ATP channel surface expression. Results showed that activation of CaMKII triggered dynamin-dependent internalization of K_ATP channels. This process required phosphorylation of threonine at 180 and 224 and an intact ³³⁰YSKF³³³ endocytosis motif of the K_ATP channel Kir6.2 pore-forming subunit. A molecular model of the μ2 subunit of the endocytosis adaptor protein, AP2, complexed with Kir6.2 predicted that μ2 docks by interaction with ³³⁰YSKF³³³ and Thr-180 on one and Thr-224 on the adjacent Kir6.2 subunit. Phosphorylation of Thr-180 and Thr-224 would favor interactions with the corresponding arginine- and lysine-rich loops on μ2. We concluded that calcium-dependent activation of CaMKII results in phosphorylation of Kir6.2, which promotes endocytosis of cardiac K_ATP channel subunits. This mechanism couples the surface expression of cardiac K_ATP channels with calcium signaling and reveals new targets to improve cardiac energy efficiency and stress resistance.     

Carbamazepine inhibits ATP-sensitive potassium channel activity by disrupting channel response to MgADP

In pancreatic β-cells, K_ATP channels consisting of Kir6.2 and SUR1 couple cell metabolism to membrane excitability and regulate insulin secretion. Sulfonylureas, insulin secretagogues used to treat type II diabetes, inhibit K_ATP channel activity primarily by abolishing the stimulatory effect of MgADP endowed by SUR1. In addition, sulfonylureas have been shown to function as pharmacological chaperones to correct channel biogenesis and trafficking defects. Recently, we reported that carbamazepine, an anticonvulsant known to inhibit voltage-gated sodium channels, has profound effects on K_ATP channels. Like sulfonylureas, carbamazepine corrects trafficking defects in channels bearing mutations in the first transmembrane domain of SUR1. Moreover, carbamazepine inhibits the activity of K_ATP channels such that rescued mutant channels are unable to open when the intracellular ATP/ADP ratio is lowered by metabolic inhibition. Here, we investigated the mechanism by which carbamazepine inhibits K_ATP channel activity. We show that carbamazepine specifically blocks channel response to MgADP. This gating effect resembles that of sulfonylureas. Our results reveal striking similarities between carbamazepine and sulfonylureas in their effects on K_ATP channel biogenesis and gating and suggest that the 2 classes of drugs may act via a converging mechanism.     

Carbamazepine inhibits ATP-sensitive potassium channel activity by disrupting channel response to MgADP

In pancreatic β-cells, K_ATP channels consisting of Kir6.2 and SUR1 couple cell metabolism to membrane excitability and regulate insulin secretion. Sulfonylureas, insulin secretagogues used to treat type II diabetes, inhibit K_ATP channel activity primarily by abolishing the stimulatory effect of MgADP endowed by SUR1. In addition, sulfonylureas have been shown to function as pharmacological chaperones to correct channel biogenesis and trafficking defects. Recently, we reported that carbamazepine, an anticonvulsant known to inhibit voltage-gated sodium channels, has profound effects on K_ATP channels. Like sulfonylureas, carbamazepine corrects trafficking defects in channels bearing mutations in the first transmembrane domain of SUR1. Moreover, carbamazepine inhibits the activity of K_ATP channels such that rescued mutant channels are unable to open when the intracellular ATP/ADP ratio is lowered by metabolic inhibition. Here, we investigated the mechanism by which carbamazepine inhibits K_ATP channel activity. We show that carbamazepine specifically blocks channel response to MgADP. This gating effect resembles that of sulfonylureas. Our results reveal striking similarities between carbamazepine and sulfonylureas in their effects on K_ATP channel biogenesis and gating and suggest that the 2 classes of drugs may act via a converging mechanism.     

KATP channels depress force by reducing action potential amplitude in mouse EDL and soleus muscle

Although ATP-sensitive K⁺ (K_ATP) channel openers depress force, channel blockers have no effect. Furthermore, the effects of channel openers on single action potentials are quite small. These facts raise questions as to whether 1) channel openers reduce force via an activation of K_ATP channels or via some nonspecific effects and 2) the reduction in force by K_ATP channels operates by changes in amplitude and duration of the action potential. To answer the first question we tested the hypothesis that pinacidil, a channel opener, does not affect force during fatigue in muscles of Kir6.2^-/- mice that have no cell membrane K_ATP channel activity. When wild-type extensor digitorum longus (EDL) and soleus muscles were stimulated to fatigue with one tetanus per second, pinacidil increased the rate at which force decreased, prevented a rise in resting tension, and improved force recovery. Pinacidil had none of these effects in Kir6.2^-/- muscles. To answer the second question, we tested the hypothesis that the effects of K_ATP channels on membrane excitability are greater during action potential trains than on single action potentials, especially during metabolic stress such as fatigue. During fatigue, M wave areas of control soleus remained constant for 90 s, suggesting no change in action potential amplitude for half of the fatigue period. In the presence of pinacidil, the decrease in M wave areas became significant within 30 s, during which time the rate of fatigue also became significantly faster compared with control muscles. It is therefore concluded that, once activated, K_ATP channels depress force and that this depression involves a reduction in action potential amplitude. Kir6.2^-/- mice; pinacidil; action potential train; M wave     

Leptin Regulates KATP Channel Trafficking in Pancreatic β-Cells by a Signaling Mechanism Involving AMP-activated Protein Kinase (AMPK) and cAMP-dependent Protein Kinase (PKA)

Pancreatic β-cells secrete insulin in response to metabolic and hormonal signals to maintain glucose homeostasis. Insulin secretion is under the control of ATP-sensitive potassium (K_ATP) channels that play key roles in setting β-cell membrane potential. Leptin, a hormone secreted by adipocytes, inhibits insulin secretion by increasing K_ATP channel conductance in β-cells. We investigated the mechanism by which leptin increases K_ATP channel conductance. We show that leptin causes a transient increase in surface expression of K_ATP channels without affecting channel gating properties. This increase results primarily from increased channel trafficking to the plasma membrane rather than reduced endocytosis of surface channels. The effect of leptin on K_ATP channels is dependent on the protein kinases AMP-activated protein kinase (AMPK) and PKA. Activation of AMPK or PKA mimics and inhibition of AMPK or PKA abrogates the effect of leptin. Leptin activates AMPK directly by increasing AMPK phosphorylation at threonine 172. Activation of PKA leads to increased channel surface expression even in the presence of AMPK inhibitors, suggesting AMPK lies upstream of PKA in the leptin signaling pathway. Leptin signaling also leads to F-actin depolymerization. Stabilization of F-actin pharmacologically occludes, whereas destabilization of F-actin simulates, the effect of leptin on K_ATP channel trafficking, indicating that leptin-induced actin reorganization underlies enhanced channel trafficking to the plasma membrane. Our study uncovers the signaling and cellular mechanism by which leptin regulates K_ATP channel trafficking to modulate β-cell function and insulin secretion.     

Modeling K(ATP) channel gating and its regulation

ATP-sensitive potassium (K_ATP) channels couple cell metabolism to plasmalemmal potassium fluxes in a variety of cell types. The activity of these channels is primarily determined by intracellular adenosine nucleotides, which have both inhibitory and stimulatory effects. The role of K_ATP channels has been studied most extensively in pancreatic beta-cells, where they link glucose metabolism to insulin secretion. Many mutations in K_ATP channel subunits (Kir6.2, SUR1) have been identified that cause either neonatal diabetes or congenital hyperinsulinism. Thus, a mechanistic understanding of K_ATP channel behavior is necessary for modeling beta-cell electrical activity and insulin release in both health and disease. Here, we review recent advances in the K_ATP channel structure and function. We focus on the molecular mechanisms of K_ATP channel gating by adenosine nucleotides, phospholipids and sulphonylureas and consider the advantages and limitations of various mathematical models of macroscopic and single-channel K_ATP currents. Finally, we outline future directions for the development of more realistic models of K_ATP channel gating.