Long-Chain CoA esters activate human pancreatic beta-cell K ATP channels: potential role in Type 2 diabetes

Abstract

Aims/hypothesis. The ATP-regulated potassium (K ATP ) channel in the pancreatic beta cell couples the metabolic state to electrical activity. The primary regulator of the K ATP channel is generally accepted to be changes in ATP/ADP ratio, where ATP inhibits and ADP activates channel activity. Recently, we showed that long-chain CoA (LC-CoA) esters form a new class of potent K ATP channel activators in rodents, as studied in inside-out patches. Methods. In this study we have investigated the effects of LC-CoA esters in human pancreatic beta cells using the inside-out and whole-cell configurations of the patch clamp technique. Results. Human K ATP channels were potently activated by acyl-CoA esters with a chain length exceeding 12 carbons. Activation by LC-CoA esters did not require the presence of Mg 2+ or adenine nucleotides. A detailed characterization of the concentration-dependent relationship showed an EC 50 of 0.7±0.1 µmol/l. Furthermore, in the presence of an ATP/ADP ratio of 10 (1.1 mmol/l total adenine nucleotides), whole-cell K ATP channel currents increased approximately sixfold following addition of 1 µmol/l LC-CoA ester. The presence of 1 µmol/l LC-CoA in the recording pipette solution increased beta-cell input conductance, from 0.5±0.2 nS to 2.5±1.3 nS. Conclusion/interpretation. Taken together, these results show that LC-CoA esters are potent activators of the K ATP channel in human pancreatic beta cells. The fact that LC-CoA esters also stimulate K ATP channel activity recorded in the whole-cell configuration, points to the ability of these compounds to have an important modulatory role of human beta-cell electrical activity under both physiological and pathophysiological conditions. [Diabetologia (2004) essential function has been included in the model of glucose-induced insulin secretion. In this model, increases in blood glucose levels lead to metabolism of glucose which generates an increase in the ATP/ADP ratio. The consensus view is that increases in the ATP/ADP ratio promote closure of the beta-cell K ATP channel, thereby depolarizing the cell membrane resulting in opening of voltage-dependent Ca 2+ channels. The subsequent rise in cytoplasmic free Ca 2+ concentration triggers a series of events leading to exocytosis of insulin. Hence, the K ATP channel provides a critical link between glucose metabolism, electrical activity and insulin secretion in the pancreatic beta cell.The most important molecular regulators of K ATP channel activity are believed to be adenine nucleo-ATP-sensitive potassium (K ATP ) channels play a key role in the coupling between cellular metabolism and electrical activity in a wide range of tissues. Since the discovery of these channels in the beta cell [1], their

Saturated and cis/trans Unsaturated Acyl CoA Esters Differentially Regulate Wild-Type and Polymorphic β-Cell ATP-Sensitive K+ Channels

“…We also found that longer-chain acyl CoAs activated the K ATP channel to a greater extent than shorter-chain acyl CoAs. These data are consistent with other reports (12,22,25), indicating that increased acyl CoA side-chain length and saturation leads to increased K ATP channel activity. However, based on results indicating that palmitoyl CoA and oleoyl CoA elicited similar K ATP channel activation, previous studies have shown that this stimulatory effect is maximal at 16 carbons in sidechain length (22).…”

“…5 are results obtained from two previous studies (21,22). Data from the Branstrom et al (22) study includes octanoyl CoA (C8:0), lauroyl CoA (C12:0), and myristoyl CoA (C14:0), while data from the Fox et al (21) study add decanoyl CoA (C10:0) to the dataset. It has been previous shown that acyl CoAs with chain lengths Ͻ14 do not significantly activate K ATP channels (12).…”

“…This is the case not only with the acyl CoAs used in this study but also for acyl CoAs of shorter-chain length used in previous studies (21,22). Using the partition coefficient between water and octanol as an indication of hydrophobicity, we fit a single exponential curve to our K ATP channel activation data that allows us to predict the effect of a given acyl CoA on the channel based on acyl chain hydrophobicity.…”

Analysis of the mouse and human acyl‐CoA thioesterase (ACOT) gene clusters shows that convergent, functional evolution results in a reduced number of human peroxisomal ACOTs1

“…The central role of free fatty acids and acyl-CoAs (the activated form of fatty acids) is evident by the numerous intracellular processes in which these molecules are key components. These processes (reviewed in (1)) include oxidation of fatty acids (α  β and ω-oxidation), biosynthesis of lipids, and allosteric regulation of a number of enzymes (2)(3)(4) and opening of K ATP -channels in human pancreatic beta-cells (5). There are, however, many processes that are activated by acyl-CoAs and inhibited by the free fatty acids or vice versa, showing the importance of maintaining the balance of these compounds in-vivo.…”

Single residue (K332A) substitution in Kir6.2 abolishes the stimulatory effect of long-chain acyl-CoA esters: indications for a long-chain acyl-CoA ester binding motif

“…LC-CoA esters activate the pancreatic beta cell K ATP channels in all reported species and cell lines, including humans [8]. The esters do not require the presence of Mg 2+ or ATP, and the site of action is separate from ADP [9].…”