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.     

Morphine induces terminal micro-opioid receptor desensitization by sustained phosphorylation of serine-375

Morphine is a poor inducer of micro-opioid receptor (MOR) internalization, but a potent inducer of cellular tolerance. Here we show that, in contrast to full agonists such as [D-Ala(2)-MePhe(4)-Gly-ol]enkephalin (DAMGO), morphine stimulated a selective phosphorylation of the carboxy-terminal residue 375 (Ser(375)). Ser(375) phosphorylation was sufficient and required for morphine-induced desensitization of MOR. In the presence of full agonists, morphine revealed partial agonistic properties and potently inhibited MOR phosphorylation and internalization. Upon removal of the drug, DAMGO-desensitized receptors were rapidly dephosphorylated. In contrast, morphine-desensitized receptors remained at the plasma membrane in a Ser(375)-phosphorylated state for prolonged periods. Thus, morphine promotes terminal MOR desensitization by inducing a persistent modification of Ser(375).     

Modulation of AMP Deaminase in Rat Hearts Subjected to Ischemia and Reperfusion by Purine Riboside

Changes in AMP deaminase (AMPD) activity influence heart function and progression of heart disease, but the underlying mechanism is unknown. We evaluated the effect of purine riboside (Purr) on the activity of AMPD in perfused rat hearts and in isolated rat cardiomyocytes. Brief perfusion of the pre-ischemic heart with 200 μ M Purr resulted in activation of AMPD, more pronounced degradation of the adenine nucleotides, and reduced recovery of the adenine nucleotide pool during reperfusion. Brief incubation of rat cardiomyocytes with 200 μ M Purr also activated AMPD, while prolonged exposure resulted in enzyme inhibition. We conclude that Purr activates AMPD, whereas metabolites of this compound may inhibit the enzyme.     

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.     

Running out of time: the decline of channel activity and nucleotide activation in adenosine triphosphate-sensitive K-channels

K_ATP channels act as key regulators of electrical excitability by coupling metabolic cues—mainly intracellular adenine nucleotide concentrations—to cellular potassium ion efflux. However, their study has been hindered by their rapid loss of activity in excised membrane patches (rundown), and by a second phenomenon, the decline of activation by Mg-nucleotides (DAMN). Degradation of PI(4,5)P₂ and other phosphoinositides is the strongest candidate for the molecular cause of rundown. Broad evidence indicates that most other determinants of rundown (e.g. phosphorylation, intracellular calcium, channel mutations that affect rundown) also act by influencing K_ATP channel regulation by phosphoinositides. Unfortunately, experimental conditions that reproducibly prevent rundown have remained elusive, necessitating post hoc data compensation. Rundown is clearly distinct from DAMN. While the former is associated with pore-forming Kir6.2 subunits, DAMN is generally a slower process involving the regulatory sulfonylurea receptor (SUR) subunits. We speculate that it arises when SUR subunits enter non-physiological conformational states associated with the loss of SUR nucleotide-binding domain dimerization following prolonged exposure to nucleotide-free conditions. This review presents new information on both rundown and DAMN, summarizes our current understanding of these processes and considers their physiological roles.This article is part of the themed issue ‘Evolution brings Ca²⁺ and ATP together to control life and death’.     

Engineered Kir6.2 mutations that correct the trafficking defect of KATP channels caused by specific SUR1 mutations

K_ATP channels consisting of Kir6.2 and SUR1 couple cell metabolism to membrane excitability and regulate insulin secretion. The molecular interactions between SUR1 and Kir6.2 that govern channel gating and biogenesis are incompletely understood. In a recent study, we showed that a SUR1 and Kir6.2 mutation pair, E203K-SUR1 and Q52E-Kir6.2, at the SUR1/Kir6.2 interface near the plasma membrane increases the ATP-sensitivity of the channel by nearly 100-fold. Here, we report the finding that the same mutation pair also suppresses channel folding/trafficking defects caused by select SUR1 mutations in the first transmembrane domain of SUR1. Analysis of the contributions from individual mutations, however, revealed that the correction effect is attributed largely to Q52E-Kir6.2 alone. Moreover, the correction is dependent on the negative charge of the substituting amino acid at the Q52 position in Kir6.2. Our study demonstrates for the first time that engineered mutations in Kir6.2 can correct the biogenesis defect caused by specific mutations in the SUR1 subunit.     

Toll样受体4在吗啡应用和耐受中的作用

Toll样受体4(Toll-like receptor 4) 是主要表达于小胶质细胞表面开启哺乳动物先天免疫反应的重要受体.近年研究表明,TLR4参与疼痛及炎症的形成.TLR4 能够被吗啡激活,其结果导致小胶质细胞活化,细胞因子合成和释放增加,从而提高疼痛感受细胞的兴奋性,减小或抵消吗啡的镇痛作用,即形成吗啡耐受.抑制TLR4可以增加吗啡的镇痛作用,减缓吗啡耐受的形成.TLR4与经典阿片受体之间存在立体选择特异性差异,(-)和(+)吗啡均能使之激活.吗啡-TLR4-胶质细胞作用链的研究为治疗吗啡耐受产生提供新的路径.     

5-Hydroxydecanoate and coenzyme A are inhibitors of native sarcolemmal KATP channels in inside-out patches

Background

5-Hydroxydecanoate (5-HD) inhibits preconditioning, and it is assumed to be a selective inhibitor of mitochondrial ATP-sensitive K⁺ (mitoK_ATP) channels. However, 5-HD is a substrate for mitochondrial outer membrane acyl-CoA synthetase, which catalyzes the reaction: 5?HD + CoA + ATP → 5-HD-CoA (5-hydroxydecanoyl-CoA) + AMP + pyrophosphate. We aimed to determine whether the reactants or principal product of this reaction modulate sarcolemmal K_ATP (sarcK_ATP) channel activity.

Methods

Single sarcK_ATP channel currents were measured in inside-out patches excised from rat ventricular myocytes. In addition, sarcK_ATP channel activity was recorded in whole-cell configuration or in giant inside-out patches excised from oocytes expressing Kir6.2/SUR2A.

Results

5-HD inhibited (IC₅₀ ∼ 30 μM) K_ATP channel activity, albeit only in the presence of (non-inhibitory) concentrations of ATP. Similarly, when the inhibitory effect of 0.2 mM ATP was reversed by 1 μM oleoyl-CoA, subsequent application of 5-HD blocked channel activity, but no effect was seen in the absence of ATP. Furthermore, we found that 1 μM coenzyme A (CoA) inhibited sarcK_ATP channels. Using giant inside-out patches, which are weakly sensitive to “contaminating” CoA, we found that Kir6.2/SUR2A channels were insensitive to 5-HD-CoA. In intact myocytes, 5-HD failed to reverse sarcK_ATP channel activation by either metabolic inhibition or rilmakalim.

General significance

SarcK_ATP channels are inhibited by 5-HD (provided that ATP is present) and CoA but insensitive to 5-HD-CoA. 5-HD is equally potent at “directly” inhibiting sarcK_ATP and mitoK_ATP channels. However, in intact cells, 5-HD fails to inhibit sarcK_ATP channels, suggesting that mitochondria are the preconditioning-relevant targets of 5-HD.     

KATP channels in mesenchymal stromal stem cells: strong up-regulation of Kir6.2 subunits upon osteogenic differentiation

The promising use of mesenchymal stromal cells (MSC) in regenerative technologies accounts for necessity of detailed study of their physiology. Proliferation and differentiation of multipotent cells often involve changes in their metabolic state. In the present study, we analyzed the expression of ATP-sensitive potassium (K_ATP) channels in MSC and upon in vitro differentiation. K_ATP channels are present in many cells and regulate a variety of cellular functions by coupling cell metabolism with membrane potential. Kir6.1, Kir6.2 and SUR2A were expressed in undifferentiated MSC, whereas SUR2B and SUR1 were not detected on cDNA and protein level. Upon adipogenic differentiation Kir6.1 and SUR2A showed a significant reduction of the amount of mRNA by 84% and 95%, respectively, whereas Kir6.2 expression was unchanged. Osteogenic differentiation strongly up-regulated Kir6.2 mRNA (28-fold) whereas Kir6.1 and SUR2A showed no significant change in expression. Quantitative Western blot analysis and immunofluorescence staining confirmed the elevated expression of Kir6.2 upon osteogenic differentiation. Taken together, expression changes of K_ATP channels may contribute to in vitro differentiation of MSC and represent changes in the metabolic state of the developing tissue.     

Functional analysis of a structural model of the ATP-binding site of the KATP channel Kir6.2 subunit

ATP-sensitive potassium (KATP) channels couple cell metabolism to electrical activity by regulating K+ flux across the plasma membrane. Channel closure is mediated by ATP, which binds to the pore-forming subunit (Kir6.2). Here we use homology modelling and ligand docking to construct a model of the Kir6.2 tetramer and identify the ATP-binding site. The model is consistent with a large amount of functional data and was further tested by mutagenesis. Ligand binding occurs at the interface between two subunits. The phosphate tail of ATP interacts with R201 and K185 in the C-terminus of one subunit, and with R50 in the N-terminus of another; the N6 atom of the adenine ring interacts with E179 and R301 in the same subunit. Mutation of residues lining the binding pocket reduced ATP-dependent channel inhibition. The model also suggests that interactions between the C-terminus of one subunit and the 'slide helix' of the adjacent subunit may be involved in ATP-dependent gating. Consistent with a role in gating, mutations in the slide helix bias the intrinsic channel conformation towards the open state.     

Role of aryl hydrocarbon receptor nuclear translocator in KATP channel-mediated insulin secretion in INS-1 insulinoma cells

Aryl hydrocarbon receptor nuclear translocator (ARNT) has been known to participate in cellular responses to xenobiotic and hypoxic stresses, as a common partner of aryl hydrocarbon receptor and hypoxia inducible factor-1/2α. Recently, it was reported that ARNT is essential for adequate insulin secretion in response to glucose input and that its expression is downregulated in the pancreatic islets of diabetic patients. In the present study, the authors addressed the mechanism by which ARNT regulates insulin secretion in the INS-1 insulinoma cell line. In ARNT knock-down cells, basal insulin release was elevated, but insulin secretion was not further stimulated by a high-glucose challenge. Electrophysiological analyses revealed that glucose-dependent membrane depolarization was impaired in these cells. Furthermore, K_ATP channel activity and expression were reduced. Of two K_ATP channel subunits, Kir6.2 was found to be positively regulated by ARNT at the mRNA and protein levels. Based on these results, the authors suggest that ARNT expresses K_ATP channel and by so doing regulates glucose-dependent insulin secretion.     

Gating of the ATP-sensitive K channel by a pore-lining phenylalanine residue

ATP-sensitive K⁺ (K_ATP) channels are gated by intracellular ATP, proton and phospholipids. The pore-forming Kir6.2 subunit has all essential machineries for channel gating by these ligands. It is known that channel gating involves the inner helix bundle of crossing in which a phenylalanine residue (Phe168) is found in the TM2 at the narrowest region of the ion-conduction pathway in the Kir6.2. Here we present evidence that Phe168-Kir6.2 functions as an ATP- and proton-activated gate via steric hindrance and hydrophobic interactions. Site-specific mutations of Phe168 to a small amino acid resulted in losses of the ATP- and proton-dependent gating, whereas the channel gating was well maintained after mutation to a bulky tryptophan, supporting the steric hindrance effect. The steric hindrance effect, though necessary, was insufficient for the gating, as mutating Phe168 to a bulky hydrophilic residue severely compromised the channel gating. Single-channel kinetics of the F168W mutant resembled the wild-type channel. Small residues increased P_open, and displayed long-lasting closures and long-lasting openings. Kinetic modeling showed that these resulted from stabilization of the channel to open and long-lived closed states, suggesting that a bulky and hydrophobic residue may lower the energy barrier for the switch between channel openings and closures. Thus, it is likely that the Phe168 acts as not only a steric hindrance gate but also potentially a facilitator of gating transitions in the Kir6.2 channel.     

Molecular determinants of ATP-sensitive potassium channel MgATPase activity: diabetes risk variants and diazoxide sensitivity

ATP-sensitive K⁺ (K_ATP) channels play an important role in insulin secretion. K_ATP channels possess intrinsic MgATPase activity that is important in regulating channel activity in response to metabolic changes, although the precise structural determinants are not clearly understood. Furthermore, the sulfonylurea receptor 1 (SUR1) S1369A diabetes risk variant increases MgATPase activity, but the molecular mechanisms remain to be determined. Therefore, we hypothesized that residue–residue interactions between 1369 and 1372, predicted from in silico modelling, influence MgATPase activity, as well as sensitivity to the clinically used drug diazoxide that is known to increase MgATPase activity. We employed a point mutagenic approach with patch-clamp and direct biochemical assays to determine interaction between residues 1369 and 1372. Mutations in residues 1369 and 1372 predicted to decrease the residue interaction elicited a significant increase in MgATPase activity, whereas mutations predicted to possess similar residue interactions to wild-type (WT) channels elicited no alterations in MgATPase activity. In contrast, mutations that were predicted to increase residue interactions resulted in significant decreases in MgATPase activity. We also determined that a single S1369K substitution in SUR1 caused MgATPase activity and diazoxide pharmacological profiles to resemble those of channels containing the SUR2A subunit isoform. Our results provide evidence, at the single residue level, for a molecular mechanism that may underlie the association of the S1369A variant with type 2 diabetes. We also show a single amino acid difference can account for the markedly different diazoxide sensitivities between channels containing either the SUR1 or SUR2A subunit isoforms.     

Mutations within the P-loop of Kir6.2 modulate the intraburst kinetics of the ATP-sensitive potassium channel

The ATP-sensitive potassium (K(ATP)) channel exhibits spontaneous bursts of rapid openings, which are separated by long closed intervals. Previous studies have shown that mutations at the internal mouth of the pore-forming (Kir6.2) subunit of this channel affect the burst duration and the long interburst closings, but do not alter the fast intraburst kinetics. In this study, we have investigated the nature of the intraburst kinetics by using recombinant Kir6.2/SUR1 K(ATP) channels heterologously expressed in Xenopus oocytes. Single-channel currents were studied in inside-out membrane patches. Mutations within the pore loop of Kir6.2 (V127T, G135F, and M137C) dramatically affected the mean open time (tau(o)) and the short closed time (tauC1) within a burst, and the number of openings per burst, but did not alter the burst duration, the interburst closed time, or the channel open probability. Thus, the V127T and M137C mutations produced longer tau(o), shorter tauC1, and fewer openings per burst, whereas the G135F mutation had the opposite effect. All three mutations also reduced the single-channel conductance: from 70 pS for the wild-type channel to 62 pS (G135F), 50 pS (M137C), and 38 pS (V127T). These results are consistent with the idea that the K(ATP) channel possesses a gate that governs the intraburst kinetics, which lies close to the selectivity filter. This gate appears to be able to operate independently of that which regulates the long interburst closings.     

十六酰胺乙醇对大鼠脑缺血再灌注损伤的抗氧化及抗凋亡作用

目的:探讨十六酰胺乙醇(Palmitoylethanolamide PEA)对大鼠脑缺血再灌注损伤的保护作用及机制。方法:将雄性SD大鼠随机分为:假手术组、药物组、模型组。采用线栓法制造大脑中动脉缺血再灌注模型,药物组于缺血后30分钟及再灌注后2小时给予PEA(10mg/Kg)腹腔注射。于再灌注24h后,对各组大鼠进行神经功能评分,TTC染色法测脑梗死体积,硫代巴比妥法测丙二醛(MDA)含量,黄嘌呤氧化酶法测超氧化物歧化酶(SOD)活性,WesternBlot法测Bcl-2和Bax蛋白含量。结果:药物组神经功能评分均值为1.33±0.49分,而模型组为2.20±0.41分,药物组神经功能评分显著低于模型组(P0.05);药物组的脑梗死体积为114.00±8.63mm3,而模型组脑梗死体积为243.40±14.19mm3,药物组脑梗死体积显著低于模型组(P0.05);药物组MDA含量为3.85±0.29nmol/mgprot,SOD活性为13.95±0.71U/mgprot,而模型组MDA含量为4.85±0.30nmol/mgprot,SOD活性为12.44±0.40U/mgprot,与模型组相比,药物组的MDA含量显著降低,而SOD活性显著增高(P0.05);药物组Bcl-2蛋白与β-action蛋白的IOD值比值为0.53±0.013%,Bax蛋白与β-action蛋白的IOD值比值为0.54±0.012%,模型组Bcl-2蛋白与β-action蛋白的IOD值比值为0.40±0.012%,Bax蛋白与β-action蛋白的IOD值比值为0.80±0.012%。药物组Bax蛋白含量显著低于模型组(P0.05),而Bcl-2蛋白含量显著高于模型组(P0.05)。结论:PEA对大鼠脑缺血再灌注损伤具有保护作用,可能是通过抗凋亡、抗氧化应激等作用实现。     

Modulation of the Permeability Transition Pore by Inhibition of the Mitochondrial KATP Channel in Liver vs. Brain Mitochondria

Inhibition of the mitochondrial K_ATP (mitoK_ATP) channel abrogates the beneficial effects of preconditioning induced by a brief episode of sublethal ischemia. We studied the effect of 5-hydroxydecanoate, a well-known inhibitor of the mitoK_ATP channel, on swelling of isolated liver and brain mitochondria. Volume changes were determined by measurement of light absorbance at 540 nm. Mitochondrial swelling induced by adding Ca²⁺ ions correlated with opening of the permeability transition pore as shown by modulation by 1 μM cyclosporin A. In brain mitochondria, 5-hydroxydecanoate did not significantly affect Ca²⁺-induced swelling. In contrast, 50 or 500 μM 5-hydroxydecanoate increased swelling of liver mitochondria by 9.7 ± 5.1% (n = 6, P = 0.057) and 29.4 ± 1.4% (n = 5, P < 0.0001), respectively. The effect of 5-hydroxydecanoate was blocked by cyclosporin A and was dependent on the presence of potassium in the medium. In medium containing 200 μM ATP to inhibit the mitoK_ATP channel, 5–hydroxydecanoate did not further increase Ca²⁺-induced swelling. We conclude that inhibition of the mitoK_ATP channel exerts its detrimental effect by facilitation of permeability transition pore opening.     

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.     

Stilbene disulfonates block ATP-sensitive K+ channels in guinea pig ventricular myocytes

Effects of stilbene disulfonates on single K_ATP channel currents were investigated in inside-out and outside-out membrane patches from guinea pig ventricular myocytes. All drugs tested, 4,4′-diisothiocyanatostilbene, 2,2′-disulfonic acid (DIDS), 4-acetamido0-4′-isothiocyanatostilbene-2,2′-disulfonic acid (SITS), 4,4′-dinitrostilbene-2,2′-disulfonic acid (DNDS), and 4,4′-diaminostilbene-2,2′-disulfonic acid (DADS), inhibited the K_ATP channel when they were applied to the intracellular, but not extracellular side of the membrane patch. Inhibitory actions of DIDS and SITS were irreversible, whereas those induced by DNDS and DADS were reversible. K_ATP channel inhibition was concentration dependent with an order of potency of DIDS>SITS ≈ DNDS > DADS; the Hill coefficient was close to unity for each drug. No change in channel conductance was observed during exposure to DIDS or DNDS; however, channel kinetics was altered. Distribution of the open time within bursts and that between bursts could be described by a single exponential relation in the absence and presence of DIDS or DNDS. The time constant of the open time within bursts was not altered, but that between bursts was decreased by DIDS (from 40.0±8.1 to 29.8±6.7 msec, P< 0.05) and by DNDS (from 43.1±9.3 to 31.9±7.1 msec, P<0.05). Distributions of closed time within bursts were also fitted to a single exponential function both in the absence and presence of drugs, while those of the closed time between bursts were fitted to a single exponential function in the absence of drugs, but a double exponential function was required in the presence of drugs. The rates of onset and development of channel inhibition by DIDS and DNDS appeared to be concentration dependent; a longer time was required to reach a new steady-state of channel activity as drug concentration was decreased. Inhibition by DIDS or DNDS was regulated by intracellular pH; inhibition was greater during acidic conditions. For DIDS (0.1 mm), the open probability (P _o) expressed as a fraction of the value before drug application was 42.9±8.3% at pH 7.4 and 8.2±6.6% at pH 6.5 (P<0.01); corresponding values for DNDS (1 mm) were 39.6±17.6 and 8.9 ±5.8%, respectively (P<0.01). From these data, we conclude that stilbene disulfonates block the K_ATP channel by binding to their target site with one-to-one stoichiometry. Similar to glibenclamide, the binding of stilbene disulfonates may reflect interpolation in an “intermediate lipid compartment” between the cytosolic drug and the site of drug action.     

大鼠海马CA1区锥体细胞上一种Ca2+依赖性KATP通道

K_ATP通道在细胞的新陈代谢与膜兴奋性的耦联中起重要作用.采用膜片钳的内面向外式记录方法,在成年大鼠海马CA1区锥体细胞上记录到一种被胞浆侧ATP和甲糖宁（tolbutamide,一种K_ATP通道阻断剂）抑制的Ca²⁺依赖性钾离子通道.在细胞膜内外的K⁺浓度均为140 mmol/L时,通道的电导为(204±21) pS,翻转电位为(3.57±1.13) mV,通道无整流性.通道开放概率及ATP对通道的抑制作用均呈现电压依赖性.该K_ATP通道与以往报道的“经典”K_ATP通道有显著不同,其活动受膜电位、胞内Ca²⁺和ATP三重调节,表明这是一种新型的K_ATP通道.上述结果表明在海马神经元上至少有两种性质不同的K_ATP通道,提示神经元可能通过不同性质的K_ATP通道感受细胞内的代谢状态,进而调节细胞膜的兴奋性.     

Reduction in number of sarcolemmal KATP channels slows cardiac action potential duration shortening under hypoxia

The cardiovascular system operates under demands ranging from conditions of rest to extreme stress. One mechanism of cardiac stress tolerance is action potential duration shortening driven by ATP-sensitive potassium (K_ATP) channels. K_ATP channel expression has a significant physiologic impact on action potential duration shortening and myocardial energy consumption in response to physiologic heart rate acceleration. However, the effect of reduced channel expression on action potential duration shortening in response to severe metabolic stress is yet to be established. Here, transgenic mice with myocardium-specific expression of a dominant negative K_ATP channel subunit were compared with littermate controls. Evaluation of K_ATP channel whole cell current and channel number/patch was assessed by patch clamp in isolated ventricular cardiomyocytes. Monophasic action potentials were monitored in retrogradely perfused, isolated hearts during the transition to hypoxic perfusate. An 80–85% reduction in cardiac K_ATP channel current density results in a similar magnitude, but significantly slower rate, of shortening of the ventricular action potential duration in response to severe hypoxia, despite no significant difference in coronary flow. Therefore, the number of functional cardiac sarcolemmal K_ATP channels is a critical determinant of the rate of adaptation of myocardial membrane excitability, with implications for optimization of cardiac energy consumption and consequent cardioprotection under conditions of severe metabolic stress.