Fast delayed rectifier potassium current is required for circadian neural activity

In mammals, the precise circadian timing of many biological processes depends on the generation of oscillations in neural activity of pacemaker cells in the suprachiasmatic nucleus (SCN). The ionic mechanisms that underlie these rhythms are largely unknown. Using the mouse brain slice preparation, we show that the magnitude of fast delayed rectifier (FDR) potassium currents has a diurnal rhythm that peaks during the day. Notably, this rhythm continues in constant darkness, providing the first demonstration of the circadian regulation of an intrinsic voltage-gated current in mammalian cells. Blocking this current prevented the daily rhythm in firing rate in SCN neurons. Kv3.1b and Kv3.2 potassium channels were widely distributed within the SCN, with higher expression during the day. We conclude that the FDR is necessary for the circadian modulation of electrical activity in SCN neurons and represents an important part of the ionic basis for the generation of rhythmic output.     

Angiotensin II modulates the delayed rectifier potassium current of guinea pig ventricular myocytes

Amplitude of the delayed rectifier (I_K) tail current measured following long (5000msec) depolarizing pulses (–10 to +50mV) was decreased 19±3% (P<0.05) in a voltage-independent manner by angiotensin II (AII) 100nM. In contrast, amplitude of tail current measured following short (250msec) depolarizing pulses to potentials > + 10mV was increased 13±3 % (P< 0.05) by AII 30nM. Deactivation kinetics of I_K measured at –30mV were altered by AII 30nM and 100nM; time constant of the faster deactivating phase ( ₁) was decreased 1.4-fold. In summary, data obtained demonstrated that physiological concentrations of AII modulates major outward potassium currents involved in cardiac repolarization. Results suggest that AII increases amplitude of the rapid component of I_k (I_Kr) but decreases its slow component I_Ks. Thus, we postulate that modulators of AII effects may exhibit direct cardiac electrophysiological properties.     

胡椒碱减轻H2O2 引起的兔心房肌细胞内向整流钾电流及超速激活延迟整流钾电流的异常改变

目的: 研究胡椒碱对H₂O₂引起的兔单个心房肌细胞内向整流钾电流(I_K1)及超速激活的延迟整流钾电流(I_KUr)异常的影响。方法: 采用全细胞膜片钳技术分析50 μmol/L H₂O₂对兔单个心房肌细胞I_K1和I_KUr的影响,并研究预先应用7 μmol/L胡椒碱对其的保护作用。结果: 7 μmol/L胡椒碱对正常兔心房肌细胞I_K1和I_KUr及其通道动力学无显著影响。在50 μmol/L H₂O₂作用下,兔心房肌细胞I_K1峰值由(-148.2±16.7)pA/pF降低至(-64.2±9.8)pA/pF (P<0.05),电流-电压曲线上移;而I_KUr峰值由(16.0±2.1)pA/pF降低至(6.1±1.4)pA/pF (P<0.05),电流-电压曲线下移,通道稳态激活曲线右移,通道稳态失活曲线左移及恢复时间减慢,而且存在频率依赖性特征。预先给予7 μmol/L胡椒碱,明显减轻H₂O₂对I_K1和I_KUr的抑制作用(P<0.01),并可减少H₂O₂对超速激活延迟整流钾通道动力学的异常影响。结论: 胡椒碱可减轻氧化应激对心房肌细胞I_K1和I_KUr的影响。     

Cardiac hypertrophy diminished the effects of isoproterenol on delayed rectifier potassium current in rat heart

We investigated the association between sympathetic nerve activity and delayed rectifier potassium current (I(K)) in hypertrophic rat hearts. Left ventricular hypertrophy was induced by a 50% constriction of suprarenal abdominal aorta for 6 weeks. The effects of isoproterenol on action potential duration (APD), I(K), and L-type calcium current (I(Ca)) were investigated using the whole-cell patch clamp technique. In hypertrophic rats, I(K) was decreased by 28.2%, resulting in significant APD(90) (90% repolarization) prolongation (sham: 55 +/- 3.9, hypertrophy: 98 +/- 11 ms, P = 0.01). Isoproterenol (100 nM)-stimulated I(K) was increased by 54.9% +/- 0.10% in sham-operated rats, but not in hypertrophic rats. On the other hand, isoproterenol increased I(Ca) in both sham-operated (77.7% +/- 7.6%) and hypertrophic rats (69.6% +/- 9.7%). Consequently, isoproterenol prolonged further APD in hypertrophic rats (98 +/- 11 vs. 145 +/- 8.6 ms, P < 0.01), but not in sham-operated rats (55 +/- 3.9 vs. 61 +/- 5.6 ms, n.s.). Forskolin (1 microM, an adenylyl cyclase stimulator) did not enhance I(K) in hypertrophic rats, but IBMX (100 microM, a nonselective phosphodiesterase inhibitor) enhanced the current (30.2 +/- 0.05%), as much as in sham-operated rats. We concluded that in hypertrophic hearts, I(K) was not increased by isoproterenol because of the enhanced activity of phosphodiesterase, which leads to excessive APD prolongation.     

Modulation of delayed rectifier potassium current, iK, by isoprenaline in rabbit isolated pacemaker cells

Permeabilized patch whole-cell voltage clamp methods were used to investigate the effects of isoprenaline (ISO) on total delayed rectifier potassium current, iK, in rabbit sino-atrial (SA) node pacemaker cells; total iK is composed of the rapidly activating iKr and the slowly activating iKs, but predominantly iKr in this species. ISO (20 nM) increased the amplitude of total iK and caused a negative shift of approximately 10 mV in the activation curve for iK, both in the absence and in the presence of 300 nM nisoldipine to block the L-type Ca2+ current, iCa,L. The same concentration (20 nM) of ISO increased the spontaneous pacemaker rate of SA node pacemaker cells by 16%. In addition to increasing the amplitude of iK, ISO (20-50 nM) also increased the rate of deactivation of this current. The stimulation of iK by ISO was reversed by 10 microM H-89, a selective protein kinase A inhibitor, but not by 200 nM bisindolymaleimide I, a selective protein kinase C inhibitor. It therefore appears that the mechanisms by which -adrenoceptor agonists increase pacemaking rate in sinoatrial node pacemaker cells include an increase in the rate of deactivation of iK in addition to the well-documented augmentation of iCa,L and the positive shift of the activation curve for the hyperpolarization-activated inward current, if. The observations are also consistent with a role for protein kinase A in the stimulation of iK by ISO in SA node cells.     

Galantamine blocks delayed rectifier,but not transient outward potassium current in rat dissociated hippocampal pyramidal neurons

Galantamine is an acetylcholinesterase inhibitor in Alzheimer's disease therapy. In the present study, we investigated the effects of galantamine on delayed rectifier potassium current (I(K(DR))) and transient outward potassium current (I(K(A))) in acutely dissociated rat hippocampal pyramidal neurons by using whole-cell patch clamp technique. I(K(DR)) was inhibited by galantamine in a concentration-dependent manner, while I(K(A)) remained unaffected. The IC(50) value for the blocking action of galantamine on I(K(DR)) was calculated as 2.0 microM. At the concentration of 10 microM, galantamine inhibited I(K(DR)) by 40.2% at +40 mV when depolarized from -50 mV, and shifted the activation curve and inactivation curve of I(K(DR)) to negative potential by -3.8 mV and -11.0 mV, respectively. In conclusion, galantamine potently inhibits I(K(DR)) but not I(K(A)) in rat hippocampal pyramidal neurons.     

Sex differences in repolarization and slow delayed rectifier potassium current and their regulation by sympathetic stimulation in rabbits

Slow delayed rectifier potassium current (I_Ks) is important in action potential (AP) repolarization and repolarization reserve. We tested the hypothesis that there are sex-specific differences in I_Ks, AP, and their regulation by β-adrenergic receptors (β-AR’s) using whole-cell patch-clamp. AP duration (APD₉₀) was significantly longer in control female (F) than in control male (M) myocytes. Isoproterenol (ISO, 500 nM) shortened APD₉₀ comparably in M and F, and was largely reversed by β₁-AR blocker CGP 20712A (CGP, 300 nM). Inhibition of I_Ks with chromanol 293B (10 μM) resulted in less APD prolongation in F at baseline (3.0 vs 8.9 %, p?<?0.05 vs M) and even in the presence of ISO (5.4 vs 20.9 %, p?<?0.05). This suggests that much of the ISO-induced APD abbreviation in F is independent of I_Ks. In F, baseline I_Ks was 42 % less and was more weakly activated by ISO (19 vs 68 % in M, p?<?0.01). ISO enhancement of I_Ks was comparably attenuated by CGP in M and F. After ovariectomy, I_Ks in F had greater enhancement by ISO (72 %), now comparable to control M. After orchiectomy, I_Ks in M was only slightly enhanced by ISO (23 %), comparable to control F. Pretreatment with thapsigargin (to block SR Ca release) had bigger impact on ISO-induced APD shortening in F than that in M (p?<?0.01). In conclusion, we found that there are sex differences in I_Ks, AP, and their regulation by β-AR’s that are modulated by sex hormones, suggesting the potential for sex-specific antiarrhythmic therapy.     

Mutations on the second chromosome affecting the Drosophila eye.

In the developing eye of Drosophila, cell interactions appear to be responsible for organising undifferentiated cells into unit eyes, or ommatidia. Extensive mutagenesis has been used to search for mutations affecting the development and differentiation of ommatidia. These mutations have been characterized using sections of adults and immunocytochemistry of imaginal discs. Fourteen loci on the second chromosome are described that affect the spacing of the preclusters, the differentiation of ommatidial cells, orientation of the ommatidia, or architecture of the adult retina, that cause retinal degeneration in larval or pupal eye discs, or that cause homeotic transformation of part of the head.     

慢性阻塞性肺疾病大鼠肺泡巨噬细胞延迟整流钾通道的活性研究

目的：探讨慢性阻塞性肺疾病（COPD）模型大鼠肺泡巨噬细胞延迟整流钾通道（KV）活性变化。 方法： 随机将大鼠分为COPD模型组和对照组,采用香烟烟雾吸入法复制大鼠COPD模型。应用全细胞电压或电流膜片钳的方法，观察和比较正常对照大鼠与COPD模型大鼠肺泡巨噬细胞（AM）KV电流活性、膜电位和电容的差异。 结果： （1）COPD组支气管肺泡灌洗液（BALF）中单个核细胞总数及AM细胞数均显著高于对照组(P<0.01)；（2）COPD大鼠BALF中AM细胞Kv电流幅度［（520.5±38.7） pA，+50 mV,n=30］显著低于对照组［（713.6±44.4） pA，+50 mV,n=30，P<0.01］；（3）COPD组AM细胞电容［（101.6±7.6）pF, n=42］与对照组［（97.4±1.6）pF,n=67］无显著差异(P>0.05)。但模型组AM膜电位［（-24.6±4.5） mV，n=18］负值显著低于对照组［（-37.9±6.1） mV,n=34，P<0.01］。 结论： COPD大鼠肺泡AM细胞KV功能下调，细胞膜电位负值降低，兴奋性升高。该机制可能与AM细胞促进COPD发病的形成机制有关。     

M_1受体参与孤啡肽抑制大鼠顶叶皮质神经元延迟整流钾电流

目的研究M受体不同亚型对孤啡肽(N/OFQ)抑制大鼠顶叶皮质神经元延迟整流钾电流(IK)作用的影响。方法采用全细胞膜片钳技术,应用M受体不同亚型阻断剂,观察M受体亚型在孤啡肽抑制大鼠顶叶皮质神经元IK中的作用。结果 (1)N/OFQ对大鼠顶叶皮质神经元IK有抑制作用,抑制率为30.8%±5.6%(P<0.01)。(2)M1受体拮抗剂哌伦西平(PIR)可减弱N/OFQ对IK的抑制作用,在指令电压为+60 mV时,PIR+N/OFQ组的IK幅度下降了15.5%±2.5%,与单独给予N/OFQ所引起的IK抑制效应相比有显著差异(P<0.05)。(3)M3受体拮抗剂4DAMP拮抗N/OFQ对IK的抑制作用不明显。结论 M1受体参与N/OFQ对大鼠顶叶皮质神经元IK的抑制作用。     

Dopamine modulation of two delayed rectifier potassium currents in a small neural network

Delayed rectifier potassium currents [I(K(V))] generate sustained, noninactivating outward currents with characteristic fast rates of activation and deactivation and play important roles in shaping spike frequency. The pyloric motor network in the stomatogastric ganglion of the spiny lobster, Panulirus interruptus, is made up of one interneuron and 13 motor neurons of five different classes. Dopamine (DA) increases the firing frequencies of the anterior burster (AB), pyloric (PY), lateral pyloric (LP), and inferior cardiac (IC) neurons and decreases the firing frequencies of the pyloric dilator (PD) and ventricular dilator (VD) neurons. In all six types of pyloric neurons, I(K(V)) is small with respect to other K(+) currents. It is made up of at least two TEA-sensitive components that show differential sensitivity to 4-aminopyridine and quinidine, and have differing thresholds of activation. One saturable component is activated at potentials above -25 mV, whereas the second component appears at more depolarized voltages and does not saturate at voltage steps up to +45 mV. The magnitude of the components varies among cell types but also shows considerable variation within a single type. A subset of PY neurons shows a marked enhancement in spike frequency with DA; DA evokes a pronounced reversible increase in I(K(V)) conductance of < or = 30% in the PY neurons studied, and on average significantly increases both components of I(K(V)). The AB neuron also shows a reversible 20% increase in the steady state I(K(V)). DA had no effect on I(K(V)) in PD, LP, VD, and IC neurons. The physiological roles of these currents and their modulation by DA are discussed.     

Macrophage migration inhibitory factor increases neuronal delayed rectifier K+ current

Macrophage migration inhibitory factor (MIF) has widespread actions in the immune, endocrine, and nervous systems. Previously, we reported that increases in the intracellular levels of MIF depress the firing of hypothalamus/brain stem neurons in culture, including the chronotropic actions of angiotensin II. The objective of this study was to investigate the effects of MIF on delayed rectifier K+ current (I(Kv)), one of the component currents whose activity contributes to neuronal firing. Intracellular perfusion of MIF (80 nM) into Sprague-Dawley rat neuronal cultures caused a significant increase in I(Kv), as measured by patch-clamp recordings. This effect was apparent by 3 min, and was maximal after 20-30 min. I(Kv) current density (pA/pF) increased from 31.58 +/- 2.36 in controls to 41.88 +/- 3.76 in MIF-treated neurons (mean +/- SE; n = 9; P < 0.01). MIF that had been inactivated by boiling did not alter I(Kv), and MIF-neutralizing antibodies abolished the action of recombinant MIF (rMIF). The stimulatory effect of MIF on I(Kv) current density was mimicked by intracellular application of either P1S-MIF (80 nM) or the peptide MIF-(50-65) (0.8-8 microM), both of which harbor the thiol-protein oxidoreductase (TPOR) activity of the MIF molecule. Conversely, neither C60S-MIF (80 nM) nor the MIF homologue D-dopachrome tautomerase (80 nM), both of which lack TPOR activity, altered I(Kv). Finally, the increase in I(Kv) produced by rMIF was abolished by the superoxide scavenger Tiron (1 mM). These studies indicate that the neuronal action of MIF includes a stimulatory action on I(Kv) that may be mediated by a TPOR/superoxide-scavenging mechanism.     

Developmental changes of the ultrarapid delayed rectifier K+ current in rat ventricular myocytes

 Recent studies have shown the presence of a 4-aminopyridine (4-AP) sensitive, ultrarapid delayed rectifier K⁺ current (I _K,ur) in adult human atria, but an apparent absence of this current in adult human ventricles. The present experiment was designed to investigate the postnatal changes of I _K,ur in rat ventricular myocytes. The presence of I _K,ur was evaluated with the use of a low concentration of 4-AP (50 μM). In 3-day-old newborns, the channel activity of rapidly activating outward current was predominantly the transient outward current (I _to). I _K,ur could be recorded in a small number of 3-day-old cells lacking I _to (16%). In 10-day-old and adult rat ventricular myocytes, almost all cells expressed I _to and its current density increased significantly with age. The fraction of cells expressing I _K,ur dramatically decreased with age and no I _K,ur-like component could be detected in the adult cells. These findings first demonstrate that the expression of I _K,ur is regulated developmentally in mammalian ventricular myocytes. Received: 21 August 1996 / Received after revision: 11 September 1996 / Accepted: 1 October 1996     

延迟整流钾通道阻断药物与维拉帕米联合应用对豚鼠心室乳头肌动作电位的影响

目的:研究IKs特异性阻断剂Chromanol 293B、IKr特异性阻断剂多非利特与L-型钙通道阻断剂维拉帕米联合应用对豚鼠心室乳头肌动作电位的作用,探讨Ⅲ类和Ⅳ类抗心律失常药物相互作用的机制。方法:用标准玻璃微电极技术记录豚鼠乳头肌的动作电位,观察不同刺激频率(0.2,0.5,1,1.25,2 Hz)对动作电位各参数的影响。结果:(1)Chromanol 293B(1,5,10μmol.L-1)能剂量依赖性的延长APD,在不同刺激频率下,Chromanol 293B 10μmol.L-1延长APD不具有频率依赖性;(2)Chromanol293B 10μmol.L-1能延长APD90,当加入多非利特0.1μmol.L-1后,显著延长APD90,增强了在低频率时的作用,表现为负性频率依赖性。(3)在结果(2)的基础上加入维拉帕米(0.1、1、2.5μmol.L-1),使APD90有一定程度的缩短,减弱了慢心率时APD90的延长作用。结论:Chromanol 293B是选择性作用于IKs的Ⅲ类抗心律失常药物,非频率依赖性的延长APD:Chromanol 293B与多非利特联合应用明显增强了延长APD的作用,表现为明显的负性频率依赖性。钙通道阻断剂维拉帕米改善了Ⅲ类抗心律失常药物的作用特性,钾和钙通道阻断剂的联合应用减弱了纯Ⅲ类抗心律失常药物导致的负性作用。     

The kinetics and rectifier properties of the slow potassium current in cardiac Purkinje fibres

1. The reversal potential of the slow outward current in Purkinje fibres varies with [K](o) in accordance with the expected potassium equilibrium potential. It is concluded that virtually all of this current is carried by potassium ions.2. The magnitude of the current is determined by two separable factors. The first factor is directly proportional to a variable obeying first-order voltage-dependent kinetics of the Hodgkin-Huxley type but with extremely long time constants. The time constants of this variable are extremely sensitive to temperature and the Q(10) over the range 26-38 degrees C is 6.3. The second factor shows inward-going rectification with a marked negative slope in the current-voltage relation beyond about 25 mV positive to the K equilibrium potential. The current-voltage relations measured at different values of [K](o) cross each other on the outward current side of the equilibrium potential.4. The changes in slow potassium current during pace-maker activity have been calculated. It is shown that the mechanism of the pace-maker potential differs in several important respects from that described by Noble's (1962) model. The negative slope in the current-voltage relation appears to be an important factor in generating the last phase of pace-maker depolarization.5. The role of the slow potassium current during the action potential and the consequences of the high temperature dependence of the kinetics are discussed.