成年大鼠海马CA1区锥体细胞K_(ATP)通道的特性

为了解成年大鼠海马CA1区锥体细胞KATP 通道的特性 ,实验采用膜片钳技术的内面向外式记录法 ,在急性分离的CA1区锥体神经元上 ,研究了可被胞浆侧ATP所抑制的钾离子单通道的特性。当细胞膜内外两侧的K 浓度均为 14 0mmol/L时 ,通道的电导为 63pS ,翻转电位为 1 71mV ,通道呈弱内向整流性。在负钳制电位时 ,通道开放时常被短时程的关闭所打断 ,而在正钳制电位时 ,这种短时程的关闭状态明显少于负钳制电位时。但通道开放概率未见明显的电压依赖性。ATP对通道活动的抑制作用呈浓度依赖性 ,抑制通道活动 5 0 %的ATP浓度为 0 1mmol/L。KATP 通道的特异性阻断剂tolbutamide (甲糖宁 ,1mmol/L)可完全阻断通道的活动 ,而KATP 通道开放剂diazoxide (二氮嗪 ,1mmol/L)则不增强通道的活动。     

大鼠海马CA1区锥体细胞上一种 Ca2+依赖性KATP通道

KATP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KATP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KATP通道与以往报道的"经典"KATP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KATP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KATP通道,提示神经元可能通过不同性质的KATP通道感受细胞内的代谢状态,进而调节细胞膜的兴奋性.     

钾通道在大鼠支气管平滑肌张力调控中作用的研究

目的：探讨延迟整流钾通道（Kv),高电导钙激活钾通道（BKCa)和ATP敏感钾通道（KATP)在大鼠支气管平滑肌张力调控中的作用。方法：以特异性钾通道阻断剂为工具,采用体外等长张力测定观察钾通道对静息和收缩状态下支气管张力的影响。结果：（1）KV阻断剂4－aminopyridine(4-AP)诱发大鼠支气管平滑肌产生浓度依赖性收缩反应,而BKCa阻断剂tetraethylammonium(TEA)和KATP阻断剂glibenclamide(Glib)对其无影响。（2）去除上皮对4－AP诱发大鼠支气管平滑肌收缩反应无影响,而钙通道阻断剂nifedipine对其有显著抑制效应。（3）在0.1mmol/L组胺或50mmol/L KCl诱发支气管平滑肌收缩之前或之后,加入TEA（1,5mmol/L)或0.1mmol/L 4-AP均显著增强二者诱发的收缩反应;而Glib(10μmol/L）对其无明显影响。结论：Kv参与大鼠支气管平滑肌静息张力的调控,而BKCa和KATP对其无影响。Kv和BKCa的关闭增强组胺及高浓度钾离子诱发大鼠离体支气管产生的收缩张力。     

KATP通道对缺氧海马CA1区神经元损伤保护作用的机制

目的:探讨KATP通道在缺氧中对海马CA1区神经元的保护作用机制。方法:比较对照组、单纯缺氧组、KATP通道激动剂 缺氧组、KATP通道阻断剂 缺氧组中神经元p53 mRNA的表达、DNA断裂、以及神经元存活情况。结果:将神经元暴露在氧浓度为0%的缺氧环境中12h,KATP通道的激动剂二氮嗪(diazoxide,100μmol/L)显著降低p53 mRNA的表达量及细胞的凋亡数量。KATP通道的阻断剂甲糖宁(tolbutamide,100μmol/L)使p53mR-NA表达量显著增加,细胞的凋亡数量也随之显著增加。p53的特异性阻断剂曲古抑菌素(trichostatin,TSA)可以逆转甲糖宁(tolbutamide,100μmol/L)的作用。结论:KATP通道可以通过下调p53 mRNA的表达水平,对缺氧中的海马CA1区神经元起到保护作用。     

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.     

中华大蟾蜍卵母细胞质膜的外向整流型钾离子通道

我们用电压箝方法研究了中华大蟾蜍卵母细胞的膜生理特性。发现卵母细胞膜去极化至-30mV及更偏正时,有一持续的外向电流出现,该电流与去极化程度约呈正比增加,当膜电位箝在20mV时其峰值达3.7±1.4μA。该电流被钾离子通道拮抗剂TEA和4-AP抑制,TEA半抑制浓度为2.6mmol/L。氯通道拮抗剂9-AC(2.5mmol/L)无抑制作用。无钙的或钙离子浓度增加三倍的胞外灌流液均对该电流无影响、该外向电流的逆转电位随胞外钾离子浓度的改变而变化。胞外钾离子浓度增加十倍,逆转电位约增加47.3mV,而胞外钠、钙或氯离子浓度的改变对逆转电位基本上无影响,因此该电流可被认为主要是电压依赖性钾离子流。取自冬眠蟾蜍的卵母细胞经孕酮诱发成熟后,电压依赖性钾离子流减小,仅为原来的1/20-1/30,而取自全年在高温饲养的蟾蜍的卵母细胞经孕酮处理后未见成熟,其电压依赖性钾离子流仅减小至原来的三分之一。     

新生大鼠下丘脑神经元L-Ca~(2 )通道电流活动特征

目的 :研究新生大鼠下丘脑神经元L Ca2 通道单通道特性 ;Ca2 通道激动剂BayK 86 44对Ca2 通道单通道特性的影响。方法 :采用神经元急性分离技术 ;用膜片钳细胞贴附式记录方式进行研究。结果 :大鼠下丘脑神经元L Ca2 通道是一种电导相对较大的Ca2 通道 ,其电导为 (2 9.5± 3.1)pS ,平均开放时间 (τ0 )为 0 .2 8ms,平均关闭时间的短关闭时间常数 (τc1)为 2 .91ms,长关闭时间常数 (τc2 )为 5 3.2 2ms。此通道几乎不存在时间依赖性失活。BayK86 44显著增加通道的开放概率 ,通道平均开放时间增加为 1.6 1ms。结论 :下丘脑神经元存在L Ca2 通道 ,该通道具有明显电压依赖性 ,而无显著的时间依赖性。通道特征与文献报道的其它神经元上L Ca2 通道相似 ,也有明显不同 ,显示下丘脑神经元L Ca2 钙通道的独特性     

氯通道在葛根素注射液致溶血反应中的作用

目的：观察阻断和激活氯通道对葛根素注射液致家兔溶血反应的影响,探讨氯通道在葛根素注射液溶血反应中的作用。方法：将不同浓度的葛根素注射液（0.75、1.5、3、6、12 mg/ml）与家兔红细胞悬液共孵育6 h,使用细胞图像记录系统观测葛根素注射液是否诱导红细胞溶血,酶标仪、流式细胞仪检测红细胞溶血率,并观测激活和阻断氯通道对葛根素注射液溶血作用的影响。结果：葛根素注射液可引起家兔红细胞体外溶血,在所观察的1.5 mg/ml~12 mg/ml范围内,溶血效应呈浓度依赖性增强（n=3,P<0.01）。氯通道阻断剂Tamoxifen （20 μmol/L）、ATP （10 mmol/L）可有效抑制葛根素注射液的溶血作用（n=3~5,P<0.01）;而使用低浓度ATP （50 μmol/L）激活氯通道,则显著增强葛根素注射液的溶血作用（n=4,P<0.01）。结论：葛根素注射液的体外溶血效应呈浓度依赖性,氯通道激活与葛根素注射液诱导的溶血反应密切相关。     

过氧化氢对蚕豆气孔运动和质膜K+通道的影响

不同浓度H2 O2 可使蚕豆 (ViciafabaL .)叶片气孔关闭 ,抑制气孔张开 ,10mmol/L的H2 O2 最有效 ,10 μmol/L的H2 O2 仍明显使气孔关闭。且 10 μmol/L的H2 O2 抑制气孔张开作用能被EGTA所消除 ,表明Ca2 参与低浓度H2 O2 使气孔关闭的过程。 2mmol/L的H2 O2 可使质膜内向K 通道电流明显减小 ,而外向K 通道电流显著增加。因此 ,H2 O2 促进蚕豆气孔关闭主要是通过抑制K 通过保卫细胞质膜内向流入 ,或加强K 外向流出实现的     

细胞外Ba~(2 )对内向整流钾通道的阻断作用

实验采用双微电极电压箝 (TEV)法研究Ba2 对非洲爪蟾卵母细胞表达的内向整流钾通道 (IRK1)的阻断作用。细胞外Ba2 浓度分别为 0 ,1,3 ,10和 10 0 μmol/L ,K 浓度分别为 10和 90mmol/L ,可见快速开通道阻断剂Ba2 对IRK1的瞬间电流 (施加电压后 1ms)的阻断作用依赖Ba2 、K 、时间和电压 ;但对IRK1的开关特性几乎无影响 ,IRK1对之不通透。三级指数拟合的结果表明 :细胞外Ba2 低浓度 ( 1和 3 μmol/L)时 ,Ba2 与K 相互竞争同一结合位点 ,随着Ba2 浓度的增加 ,时间常数不增加但拟合的权数却呈浓度依赖性增加 ,所以失活过程随Ba2 浓度的增加越来越快 ;细胞外Ba2 高浓度 ( 10和 10 0 μmol/L)时 ,时间常数随Ba2 浓度的增加而减少 ,拟合的权数却呈浓度依赖性减少 ,失活过程也越来越快 ,说明Ba2 作用位点由通道的表面进入了通道更深的部位。上述结果提示 ,Ba2 对IRK1的阻断存在两种不同的机制。细胞外K 浓度为 90mmol/L和Ba2 浓度为 3 0 μmol/L时 ,Mg2 或Mn2 可与Ba2 争夺结合位点 ,随着Mg2 或Mn2 浓度增加 ,失活过程逐渐减缓 ,Ba2 在通道中的结合点也逐渐离开通道 ,Mg2 能而Mn2 不能进入通道较深处阻断通道 ,说明IRK1中有多离子阻断形式     

Syntaxin-1A inhibits cardiac KATP channels by its actions on nucleotide binding folds 1 and 2 of sulfonylurea receptor 2A

ATP-sensitive potassium (KATP) channels couple the metabolic status of the cell to its membrane potential to regulate a number of cell actions, including secretion (neurons and neuroendocrine cells) and muscle contractility (skeletal, cardiac, and vascular smooth muscle). KATP channels consist of regulatory sulfonylurea receptors (SUR) and pore-forming (Kir6.X) subunits. We recently reported (Pasyk, E. A., Kang, Y., Huang, X., Cui, N., Sheu, L., and Gaisano, H. Y. (2004) J. Biol. Chem. 279, 4234-4240) that syntaxin-1A (Syn-1A), known to mediate exocytotic fusion, was capable of binding the nucleotide binding folds (NBF1 and C-terminal NBF2) of SUR1 to inhibit the KATP channels in insulin-secreting pancreatic islet beta cells. This prompted us to examine whether Syn-1A might modulate cardiac SUR2A/KATP channels. Here, we show that Syn-1A is present in the plasma membrane of rat cardiac myocytes and binds the SUR2A protein (of rat brain, heart, and human embryonic kidney 293 cells expressing SUR2A/Kir6. 2) at its NBF1 and NBF2 domains to decrease KATP channel activation. Unlike islet beta cells, in which Syn-1A inhibition of the channel activity was apparently mediated only via NBF1 and not NBF2 of SUR1, both exogenous recombinant NBF1 and NBF2 of SUR2A were found to abolish the inhibitory actions of Syn-1A on K(ATP) channels in rat cardiac myocytes and HEK293 cells expressing SUR2A/Kir6.2. Together with our recent report, this study suggests that Syn-1A binds both NBFs of SUR1 and SUR2A but appears to exhibit distinct interactions with NBF2 of these SUR proteins in modulating the KATP channels in islet beta cells and cardiac myocytes.     

ATPase activity of the sulfonylurea receptor: a catalytic function for the KATP channel complex.

ATP-sensitive K+ (KATP) channels are unique metabolic sensors formed by association of Kir6.2, an inwardly rectifying K+ channel, and the sulfonylurea receptor SUR, an ATP binding cassette protein. We identified an ATPase activity in immunoprecipitates of cardiac KATP channels and in purified fusion proteins containing nucleotide binding domains NBD1 and NBD2 of the cardiac SUR2A isoform. NBD2 hydrolyzed ATP with a twofold higher rate compared to NBD1. The ATPase required Mg2+ and was insensitive to ouabain, oligomycin, thapsigargin, or levamisole. K1348A and D1469N mutations in NBD2 reduced ATPase activity and produced channels with increased sensitivity to ATP. KATP channel openers, which bind to SUR, promoted ATPase activity in purified sarcolemma. At higher concentrations, openers reduced ATPase activity, possibly through stabilization of MgADP at the channel site. K1348A and D1469N mutations attenuated the effect of openers on KATP channel activity. Opener-induced channel activation was also inhibited by the creatine kinase/creatine phosphate system that removes ADP from the channel complex. Thus, the KATP channel complex functions not only as a K+ conductance, but also as an enzyme regulating nucleotide-dependent channel gating through an intrinsic ATPase activity of the SUR subunit. Modulation of the channel ATPase activity and/or scavenging the product of the ATPase reaction provide novel means to regulate cellular functions associated with KATP channel opening.     

A K ATP channel-dependent pathway within alpha cells regulates glucagon release from both rodent and human islets of Langerhans

Glucagon, secreted from pancreatic islet alpha cells, stimulates gluconeogenesis and liver glycogen breakdown. The mechanism regulating glucagon release is debated, and variously attributed to neuronal control, paracrine control by neighbouring beta cells, or to an intrinsic glucose sensing by the alpha cells themselves. We examined hormone secretion and Ca(2+) responses of alpha and beta cells within intact rodent and human islets. Glucose-dependent suppression of glucagon release persisted when paracrine GABA or Zn(2+) signalling was blocked, but was reversed by low concentrations (1-20 muM) of the ATP-sensitive K(+) (KATP) channel opener diazoxide, which had no effect on insulin release or beta cell responses. This effect was prevented by the KATP channel blocker tolbutamide (100 muM). Higher diazoxide concentrations (>/=30 muM) decreased glucagon and insulin secretion, and alpha- and beta-cell Ca(2+) responses, in parallel. In the absence of glucose, tolbutamide at low concentrations (<1 muM) stimulated glucagon secretion, whereas high concentrations (>10 muM) were inhibitory. In the presence of a maximally inhibitory concentration of tolbutamide (0.5 mM), glucose had no additional suppressive effect. Downstream of the KATP channel, inhibition of voltage-gated Na(+) (TTX) and N-type Ca(2+) channels (omega-conotoxin), but not L-type Ca(2+) channels (nifedipine), prevented glucagon secretion. Both the N-type Ca(2+) channels and alpha-cell exocytosis were inactivated at depolarised membrane potentials. Rodent and human glucagon secretion is regulated by an alpha-cell KATP channel-dependent mechanism. We propose that elevated glucose reduces electrical activity and exocytosis via depolarisation-induced inactivation of ion channels involved in action potential firing and secretion.     

KATP channels gated by intracellular nucleotides and phospholipids.

The KATP channel is a heterooctamer composed of two different subunits, four inwardly rectifying K+ channel subunits, either Kir6. 1 or Kir6.2, and four sulfonylurea receptors (SUR), which belong to the family of ABC transporters. This unusual molecular architecture is related to the complex gating behaviour of these channels. Intracellular ATP inhibits KATP channels by binding to the Kir6.x subunits, whereas Mg-ADP increases channel activity by a hydrolysis reaction at the SUR. This ATP/ADP dependence allows KATP channels to link metabolism to excitability, which is important for many physiological functions, such as insulin secretion and cell protection during periods of ischemic stress. Recent work has uncovered a new class of regulatory molecules for KATP channel gating. Membrane phospholipids such as phosphoinositol 4, 5-bisphosphate and phosphatidylinositiol 4-monophosphate were found to interact with KATP channels resulting in increased open probability and markedly reduced ATP sensitivity. The membrane concentration of these phospholipids is regulated by a set of enzymes comprising phospholipases, phospholipid phosphatases and phospholipid kinases providing a possible mechanism for control of cell excitability through signal transduction pathways that modulate activity of these enzymes. This review discusses the mechanisms and molecular determinants that underlie gating of KATP channel by nucleotides and phospholipids and their physiological implications.     

腺苷易化大鼠颈动脉窦压力感受器的活动

在36只麻醉大鼠,以隔离灌流颈动脉窦区记录窦神经传入放电的方法观察了腺苷（adenosine,Ado）对颈动脉窦压力感受器传入放电的影响。所得结果如下：（1）以75μmol／LAdo隔离灌流大鼠左侧颈动脉窦区时,窦内压-窦神经传入放电积分（ISP－ISNA）关系曲线向左上方移位,曲线最大斜率（PS）由（18．75±0．12）％／kPa增至（22．21±0．11）％／kPa（P＜0．001）,最大积分值（PIV）由（209．83±2．57）％增至（239．17±1．75）％;阈压（TP）和饱和压（SP）则分别从（8．57±0．24）和（22．99±0．34）下降至（7．15±0．23）kPa（P＜0．001）和（21．21±0,43）kPa（P＜0．01）。再分别以125和175μmol／LAdo灌流,机能曲线进一步向左上方移位,PS、TP和SP的变化均呈明显的剂量依赖性。（2）用腺苷选择性A1受体拮抗剂8－cyclopentyl－1,3－dipropylxanthine（0．134mmol／L）预处理后,Ado的上述效应即被阻断。（3）先给予KATP通道阻断剂格列苯脲（10μmol／L）亦可取消腔苷对窦神经传入放电的影响。结果表明,在体隔离灌流大鼠颈动脉窦区条件下,Ado对颈动脉窦压力感受器活动有易化作用,此作用似与腺苷A1受体介导的KATP通道开放有关。     

内皮素对麻醉大鼠颈动脉窦压力感受器活动的影响

在麻醉大鼠隔离灌流颈动脉窦区条件下记录窦神经传入放电,观察内皮素（ＥＴ－１）对动脉压力感受器活动的影响。结果如下：（１）在颈动脉窦区灌流１ｎｍｏｌ／Ｌ ＥＴ－１时,压力感受器机能曲线向左上方移位,曲线的最大斜率（ＰＳ）增加,窦神经传入放电最大积分值（ＰＩＶ）增大。由此提示,这一剂量的ＥＴ－１对压力感受器活动有易化作用。（２）用１０ｎｍｏｌ／Ｌ ＥＴ－１灌流时,压力感受器机能曲线则向右下方移位,ＰＳ     

Surface charge and properties of cardiac ATP-sensitive K+ channels

ATP-sensitive K+ (KATP) channels are present in a wide variety of tissues. The sensitivity of these channels to closure by cytosolic ATP (ATPi) varies significantly among different tissues and even within the same tissue. The purpose of this study was to test the hypothesis that negative surface charges modulate the sensitivity of the KATP channels to ATPi by influencing surface potential in the vicinity of the ATP- binding site(s) of the channel. Unitary currents through KATP channels were measured in inside-out membrane patches excised from rabbit ventricular myocytes using the patch-clamp technique. Agents known to be effective at screening negative surface charges were applied to the cytosolic surface of the patches, and their effects on ATP sensitivity were examined. These agents included Mg2+ (2-15 mM), Ba2+ (2-10 mM), and the polycations protamine (0.01-10 microM), poly-L-lysine (500 microM), and poly-L-arginine (0.5 microM). The divalent cations and the various polycations all dramatically reduced the concentration of ATPi required to half-maximally suppress current through KATP channels (Kd), from approximately 100 microM in the absence of these agents to 1.6-8 microM in their presence. The effects were dose dependent. Protamine also reduced the sensitivity of KATP channels to block by cytosolic ADP. The sensitivity of KATP channels to block by ATP was independent of membrane potential, suggesting that the ATP-binding site is not located within the transmembrane voltage field. The effects of the polycation poly-L-lysine on ATP sensitivity were also independent of membrane potential or the direction (inward or outward) of current through KATP channels. In addition to increasing ATP sensitivity, Mg2+, Ba2+, and the polycations all caused dose-dependent block of inward and outward currents through KATP channels over similar concentration ranges as their effects on ATP sensitivity. The block of inward current by polycations was not associated with reduction of single-channel conductance or evidence of fast open channel block. However, the polycations did cause a modest reduction in single-channel conductance of outward current. These results are consistent with the presence of negative surface charges that reduce the local ATP concentration at the ATP-binding site(s) on the channel, relative to the bulk cytosolic ATP concentration. Screening these negative surface charges with divalent cations or polycations decreases the local ATP gradient, resulting in a decrease in the apparent Kd for ATP.(ABSTRACT TRUNCATED AT 400 WORDS)     

组胺拮抗剂对小鼠ATP-敏感性钾离子通道的影响

目的观察比较3种组胺拮抗剂对缺血性心肌细胞的ATP-敏感性钾离子通道中的影响。方法利用急性酶解法分离小鼠心室肌细胞。结果组胺拮抗剂pyrilamine、chlorpheniramine及diphenhydramine均可抑制ATP-敏感性钾离子通道的活性,抑制程度为pyrilamine〉chlorpheniramine〉diphenhydramine。组胺对KATP通道活性无影响。结论第一代的组胺拮抗剂（pyrilamine、chlorpheniramine及diphenhydramine）对KATP通道活性有抑制作用,其抑制作用与膜上H1受体无关。     

Ankyrin regulates KATP channel membrane trafficking and gating in excitable cells

KATP channels play critical roles in many cellular functions by coupling cell metabolic status to electrical activity. First discovered in cardiomyocytes 1, KATP channels (comprised of Kir6.x and SUR subunits) have since been found in many other tissues, including pancreatic beta cells, skeletal muscle, smooth muscle, brain, pituitary, and kidney. By linking cellular metabolic state with membrane potential, KATP channels are able to regulate a number of cellular functions such as hormone secretion, vascular tone, and excitability. Specifically, a reduction in metabolism causes a decrease in the ATP:ADP ratio, opening of KATP channels and allowing K+ efflux, membrane hyperpolarization, and suppression of electrical activity. Conversely, increased cellular metabolism causes a decrease in the ATP:ADP ratio that leads to closure of the KATP channel, membrane depolarization, and stimulation of cell electrical activity.     

A novel KCNJ11 mutation associated with congenital hyperinsulinism reduces the intrinsic open probability of beta-cell ATP-sensitive potassium channels

The beta-cell ATP-sensitive potassium (KATP) channel controls insulin secretion by linking glucose metabolism to membrane excitability. Loss of KATP channel function due to mutations in ABCC8 or KCNJ11, genes that encode the sulfonylurea receptor 1 or the inward rectifier Kir6.2 subunit of the channel, is a major cause of congenital hyperinsulinism. Here, we report identification of a novel KCNJ11 mutation associated with the disease that renders a missense mutation, F55L, in the Kir6.2 protein. Mutant channels reconstituted in COS cells exhibited a wild-type-like surface expression level and normal sensitivity to ATP, MgADP, and diazoxide. However, the intrinsic open probability of the mutant channel was greatly reduced, by approximately 10-fold. This low open probability defect could be reversed by application of phosphatidylinositol 4,5-bisphosphates or oleoyl-CoA to the cytoplasmic face of the channel, indicating that reduced channel response to membrane phospholipids and/or long chain acyl-CoAs underlies the low intrinsic open probability in the mutant. Our findings reveal a novel molecular mechanism for loss of KATP channel function and congenital hyperinsulinism and support the importance of phospholipids and/or long chain acyl-CoAs in setting the physiological activity of beta-cell KATP channels. The F55L mutation is located in the slide helix of Kir6.2. Several permanent neonatal diabetes-associated mutations found in the same structure have the opposite effect of increasing intrinsic channel open probability. Our results also highlight the critical role of the Kir6.2 slide helix in determining the intrinsic open probability of KATP channels.