Molecular basis of inward rectification: structural features of the blocker defined by extended polyamine analogs

Polyamines cause inward rectification of Kir K(+) channels by blocking deep within the channel pore. We investigated structural constraints of polyamine block of strongly rectifying mutant K(ATP) channels (Kir6.2[L164C,N160D,C166S] + SUR1). We studied three groups of polyamine analogs: 1) conformationally restricted linear tetra-amines with a cycloalkyl or alkene group between the second and third amines (CGC-11047, CGC-11093, CGC-11099, and CGC-11098), 2) conformationally restricted linear deca-amines with a cycloalkyl or alkene group between the fifth and sixth amines (CGC-11150, CGC-11179, and CGC-11241), and 3) cyclic tetra-amines (CGC-11174, CGC-11197, CGC-11199, and CGC-11254). All linear analogs cause a voltage-dependent block similar to that of spermine, but slightly weaker (at 1 microM, V(1/2) for spermine block = -10 +/- 1 mV, Z = 2.9 +/- 0.1, n = 19; V(1/2) for analogs varies from polyamine -7 to +10 mV, Z = 2.6-3.9). These data indicate tolerance for conformational restriction and an upper limit to the voltage dependence of the blocking process. There was no voltage-dependent block by the cyclic compounds; instead, they induce irreversible rundown of the current. Structural models of Kir channels suggest that a narrow entry at the top of the cytoplasmic pore may exclude cyclic analogs from the inner cavity, thereby explaining the structure-activity relationship that we observe.     

Effect of maitotoxin on calcium current and background inward current in isolated ventricular rat myocytes

Maitotoxin (MTX) irreversibly suppressed the voltage-dependent calcium current after a variable delay, an effect which was preceded, in 61% of the cells, by a transient increase in calcium current partly attributable to a shift (4-7 mV) of the activation curve towards negative potentials. MTX also induced the development of a voltage-independent background inward current which did not occur in the absence of external calcium and was reduced by removal of external sodium, by calcium channel blockers and by high concentrations of quinidine. MTX-induced single channel activity consisted of long lasting bursts of inward current. Channel activity was voltage-independent, with a unitary conductance of 14 pS and an extrapolated reversal potential of +16 mV. Single-channel current amplitude was not detectably reduced in the absence of external calcium but strongly reduced in the absence of external sodium, in the presence of 2 mM nickel or when external sodium was replaced by 96 mM calcium or 50 mM barium. The channel activity was also inhibited by quinidine. It is concluded that MTX alters, then suppresses the voltage-activated calcium current and induces the development of a voltage-independent inward current, part of which results from the opening of nickel-sensitive cation channels, mostly permeable to sodium ions.     

Caffeine-induced decreases in the inward rectifier potassium and the inward calcium currents in rat ventricular myocytes.

The effects of high (20 mM) concentrations of caffeine were studied on the transmembrane voltage and currents in rat single ventricular myocytes by the whole cell configuration of the patch clamp technique. Rapid application of caffeine released Ca2+ from the sarcoplasmic reticulum and induced a Ni(2+)-sensitive transient inward current with concomitant change of the transmembrane voltage from -72.6 +/- 0.4 to -68.0 +/- 0.6 mV (n = 4). Maintained application of caffeine lengthened the action potential duration (APD90) from 66.7 +/- 16.9 to 135.1 +/- 34.1 ms (n = 4) and depressed the amplitude of both the inward rectifier potassium and the inward calcium currents. It is concluded that these effects of caffeine should be recognized when it is used as a tool to study electromechanical coupling.     

Elecropharmacology of taurine on the hyperpolarization-activated inward current and the sustained inward current in spontaneously beating rat sino-atrial nodal cells

Modulation by taurine of the pacemaking activity and the underlying ionic currents, especially a hyperpolarization-activated inward current (I(f)) and a sustained inward current (I(ST)), in rat sino-atrial (SA) nodal cells was investigated at different pCa levels using a patch-clamp technique. Increasing pCa levels from 10 to 6 stimulated the spontaneous activity and simultaneously increased the I(f). Application of taurine depressed more strongly the spontaneous activity at higher pCa levels. At all pCa levels, however, taurine (20 mM) increased the I(f) by 60.1 +/- 1.7% (n = 8, P<0.001) at pCa 10 and by 48.0 +/- 1.4% (n = 8, P<0.01) at pCa 7. At pCa 7, taurine (10 and 20 mM) decreased the sustained inward current (I(ST)) by 13.3 +/- 1.1% (n = 5, P<0.05) and by 38.1 +/- 2.4% (n = 5, P<0.01), respectively. Taurine (20 mM) inhibited the L-type Ca(2+) current (I(CaL)) by 35.8 +/- 2.5% (n = 8, P<0.01), whereas taurine enhanced the T-type Ca(2+) current (I(CaT)) by 29.3 +/- 2.9% (n = 8, P<0.05). Also, taurine at pCa 7 decreased the delayed rectifier K(+) current; taurine at 20 mM inhibited the rapidly activated K(+) current (I(Kr)) by 55.6 +/- 3.3% (n = 6, P<0.001), but not the slowly activated K(+) current (I(Ks)). Taurine often elicited dysrhythmias, dependent on taurine's concentrations and pCa levels. These results indicate that taurine causes a negative chronotropic effect due to the inhibitions of the pacemaking ionic currents such as I(CaL), I(Kr) and I(ST), and suggest that the I(f) and I(CaT) currents make a minor contribution to pacemaking activity in rat SA nodal cells.     

基层医院临床药师在抗菌药物专项整治活动中的作用

目的探讨药师在基层医院专项整治活动中的作用。方法抽取了基层医院2012年2月至4月份的用药数据,以用药频度（DDDs）排序出前20位药品。结果用药频度均得到了明显的减少,对于I类切口手术预防用药出现了较大的变化,合格率由2.13%上升至54.12%。结论药师应充分发挥自身优势,为抗菌药物专项整治活动和合理应用抗生素提供重要药学服务     

丙基丁基多巴胺对心肌内向整流钾电流的抑制作用(英文)

研究丙基了基多巴胺（ＰＢＤＡ）对内向整流钾电流（Ｉｋ１）的影响．方法：应用缓慢斜坡去极化脉冲程序测定离体豚鼠心室肌细胞准稳态电流－电压关系曲线．结果： ＰＢＤＡ ５, ５０和１００μｍｏｌ· Ｌ－１浓度依赖性地降低了心肌内向整流钾电流,表明该药对Ｉｋ１具有抑制作用ＰＢＤＡ对于Ｉｋ１的这种抑制效应不被多巴胺Ｄ２受体选择性阻断剂多潘立酮所阻断．结论：ＰＢＤＡ直接抑制Ｉｋ１,与多巴胺Ｄ２受体无关。     

Direct block of inward rectifier potassium channels by nicotine

Nicotine has been shown to depolarize membrane potential and to lengthen action potential duration in isolated cardiac preparations. To investigate whether this is a consequence of direct interaction of nicotine with inward rectifier K(+) channels which are a key determinant of membrane potentials, we assessed the effects of nicotine on two cloned human inward rectifier K(+) channels, Kir2.1 and Kir2.2, expressed in Xenopus oocytes and the native inward rectifier K(+) current I(K1) in canine ventricular myocytes. Nicotine suppressed Kir2.1-expressed currents at varying potentials negative to -20 mV, with more pronounced effects on the outward current between -70 and -20 mV relative to the inward current at hyperpolarized potentials (below -70 mV). The inhibition was concentration dependent. For the outward currents recorded at -50 mV, the IC50 was 165 +/- 18 microM. Similar effects of nicotine were observed for Kir2.2. A more potent effect was seen with I(K1) in canine myocytes. Significant blockade ( approximately 60%) was found at a concentration as low as 0.5 microM and the IC50 was 4.0 +/- 0.4 microM. The effects in both oocytes and myocytes were partially reversible upon washout of nicotine. Antagonists of nicotinic receptors (mecamylamine, 100 microM), muscarinic receptors (atropine, 1 microM), and beta-adrenergic receptors (propranolol, 1 microM) all failed to restore the depressed currents, suggesting that nicotine acted directly on Kir channels, independent of catecholamine release. This property of nicotine may explain its membrane-depolarizing and action potential duration-prolonging effects in cardiac cells and may contribute in part to its ability to promote propensity for cardiac arrhythmias.     

NMDA enhances a depolarization-activated inward current in subthalamic neurons

Previous studies have shown that N-methyl-D-aspartate (NMDA) receptor stimulation evokes Ca2+- and Na+-dependent burst firing in subthalamic nucleus (STN) neurons. Using whole-cell patch pipettes to record currents under voltage-clamp, we identified a time-dependent depolarization-activated inward current (DIC) that may underlie NMDA-induced burst firing in STN neurons in rat brain slices. Continuous superfusion with NMDA (20 microM) elicited a marked TTX-insensitive inward current when the membrane was depolarized to the level of -70 or -50 mV, from a holding potential of -100 mV. This current had a long duration, and its peak amplitude occurred at a test potential of -60 mV. DIC could not be evoked using the non-NMDA receptor agonist D,L-alpha-amino-3-hydroxy-5-methylisoxalone-4-propionic acid (AMPA). DIC was blocked by either intracellular BAPTA or by removal of extracellular Ca2+, but selective blockers of T-type (mibefradil), L-type (nifedipine) and N-type (omega-conotoxin GVIA) Ca2+ channels did not. Perfusing slices with a low extracellular concentration of sodium abolished the NMDA-induced DIC, implying that both Ca2+ and Na+ are necessary for the expression of DIC. Transient receptor potential (TRP) channel blockers flufenamic acid and SKF96365 severely reduced DIC amplitude, whereas NMDA-gated currents were either increased or were unchanged. These results suggest that the activation of NMDA receptors enhances a Ca2+-activated non-selective cation current that may be mediated by a member of the TRP channel family in STN neurons.     

青蒿素对克隆的内向整流钾通道的抑制作用

采用双电极电压钳技术观测了青蒿素对表达于非洲蛙卵的克隆内向整流钾通道(K_ir2.1)的影响. 当蛙卵注射K_ir2.1 cRNA后灌注不同浓度青蒿素时, 青蒿素呈浓度依赖关系降低K_ir2.1钾通道在非洲蛙卵细胞膜的功能表达. 青蒿素阻断K_ir2.1钾通道亦呈电压依赖性. 当指令电压为-140, -130和-120 mV时, 5和50 μmol·L^-1的青蒿素可使K_ir2.1钾通道的内向电流分别下降14.2%, 34.5%; 12.0%, 24.6%; 4.3%, 19.1%. 当指令电压为-50, -40和-30 mV时, 5和50 μmol·L^-1的青蒿素则使K_ir2.1钾通道的外向电流分别增加22.2%, 72.2%; 28.0%, 80.0%; 24.1%, 69.0%. 青蒿素对K_ir2.1通道的阻断作用在用正常灌注液冲洗后可恢复. 青蒿素的抗心律失常作用与它阻断K_ir2.1通道电流有关.     

Glutamate-induced inward current in a clonal neuroblastoma cell line.

The presence of glutamate-induced electrophysiological responses was examined in eight clonal neuroblastoma cell lines with the whole-cell voltage clamp technique. Only N2A cells responded to glutamate superfusion with a concentration-dependent, reversible inward current. Superfusion with the analogues kainic acid, quisqualic acid and N-methyl-D-aspartic acid also evoked inward currents but they had a smaller amplitude. The results indicate that N2A neuroblastoma cells could serve as an in vitro model to study the functional properties of glutamate receptors and associated ion channels.     

专项整治活动前后我院抗菌药物使用情况比较分析

目的了解卫生部抗菌药物临床应用专项整治活动以来我院抗菌药物的使用情况,为抗菌药物的合理应用和科学管理提供依据。方法根据该院计算机管理系统提供的抗菌药物用药信息,采用限定日剂量(DDD)和金额排序等指标,对2011—2012年该院抗菌药物的使用情况进行归类、统计、分析。结果该院各类抗菌药物耗费金额所占的比例以头孢菌素类为主,两年分别占58.65%和55.63%;2011年抗菌药物消耗总额占全年药品总额的比例为28.79%,2012年抗菌药物消耗总额占全年药品总额的比例为25.50%,同比下降了3.29%。与2011年相比,2012年该院抗菌药物使用率、使用强度稳步下降。结论该院抗菌药物临床应用专项治理活动初见成效,使用基本合理,但尚须加以改进。     

丙基丁基多巴胺对心肌内向整流钾电流的抑制作用

研究丙基丁基多巴胺对内向整流钾电流的影响。方法：应用缓慢斜坡去极化脉冲程序测定离体豚鼠心室肌细胞准稳态电流－电压关系曲线。结果：ＰＢＤＡ５,５０和１００μｍｏｌ．Ｌ＾－１浓度依赖性地降低了心肌内向整流钾电流,表明该药对ＩＫ１具有抑制作用。     

专项整治前后会阴侧切术抗菌药物用药情况的调查分析

目的：评价开展抗菌药物专项整治活动对本院会阴侧切术患者抗菌药物合理应用的作用。方法回顾性分析本院开展抗菌药物专项整治前（2010年10~12月）、后（2013年10~12月）会阴侧切术患者的临床资料和抗菌药物应用情况。结果本院经过抗菌药物专项整治后,会阴侧切术患者的抗菌药物应用率由整治前的51.0%下降至整治后的25.2%;以预防用药为目的抗菌药物使用率由整治前的48.6%下降至整治后的22.6%;单药应用率由整治前的50.4%下降至整治后的25.0%;非限制使用类抗菌药物所占比例由50.6%降至24.2%（P＜0.05）;限制使用类抗菌药物所占比例由0.4%升至1.0%;二联用药率由整治前的0.6%下降至整治后的0.2%（P＞0.05）。结论抗菌药物专项整治对本院会阴侧切术患者合理应用抗菌药物有明显促进作用,会阴侧切术抗菌药物使用率呈明显下降趋势,促进了临床合理用药。     

Somatostatin decreases the calcium inward current in guinea-pig atria.

1. The effects of somatostatin on mechanical and electrophysiological responses were studied in guinea-pig atrial muscle preparations and single cells. 2. Somatostatin (greater than or equal to 10(-8) M) decreased the twitch contraction in a concentration-dependent manner in electrically driven left atria and spontaneously beating right atria. However, the beating rate was not affected. 3. The negative inotropic effect of somatostatin was transient. Desensitization to this agent developed slowly during continuous exposure to the peptide. 4. In single atrial cells, somatostatin significantly shortened the action potential duration, but the resting potential and action potential amplitude were not affected. 5. Under whole cell voltage-clamp conditions, somatostatin decreased the calcium inward current without affecting the sodium and potassium currents. 6. These results suggest that somatostatin selectively acts on the calcium channel of guinea-pig atrial cells to reduce the calcium inward current, which in turn gives rise to the negative inotropic effect.     

瞬态内向电流 ,迟后除极与钙调蛋白激酶(英文)

心律失常发生在各种细胞内钙增加的情况下 ,包括心肌缺血 ,强心甙中毒 ,充血性心衰以及各种原因所致动作电位时程过度延长 .多功能钙 /钙调蛋白依赖性蛋白激酶Ⅱ (钙调蛋白激酶 )是细胞内钙的重要生理靶位和参与调节细胞内钙稳态的关键控制因素 ,包括L型钙电流 ,肌浆网钙释放和摄取 .由于钙调蛋白激酶能影响各种钙敏感离子电流及导致心律失常 ,有可能是一种有效的抗心律失常药物作用靶位 .瞬态内向电流激发迟后除极 ,有可能是钙超负荷心律失常的原因 .有关瞬态内向电流的实质仍有争议 ,但似乎在不同的实验条件下 ,是由不同的离子电流所引起 .这些电流多由细胞内钙激活 ,因为瞬态内向电流总是随着细胞内钙增加而产生 .我们的研究表明在兔心室细胞有三种钙敏感电流有可能与瞬态内向电流产生有关 ,它们是钠 /钙交换电流 ,钙激活的氯电流以及钙激活的非选择性阳离子电流 .我们还发现在生理溶液条件下产生的瞬态内向电流可被钙调蛋白激酶抑制肽所抑制 .我们的实验结果支持这一假说 :钙调蛋白激酶能增强临床相关条件下的瞬态内向电流 ,即细胞内钙增加条件下的瞬态内向电流 ,因而发挥一个致心律失常信号分子的作用     

Involvement of inward rectifier and M-type currents in carbachol-induced epileptiform synchronization

Exposure to cholinergic agonists is a widely used paradigm to induce epileptogenesis in vivo and synchronous activity in brain slices maintained in vitro. However, the mechanisms underlying these effects remain unclear. Here, we used field potential recordings from the lateral entorhinal cortex in horizontal rat brain slices to explore whether two different K⁺ currents regulated by muscarinic receptor activation, the inward rectifier (K_IR) and the M-type (K_M) currents, have a role in carbachol (CCh)-induced field activity, a prototypical model of cholinergic-dependent epileptiform synchronization. To establish whether K_IR or K_M blockade could replicate CCh effects, we exposed slices to blockers of these currents in the absence of CCh. K_IR channel blockade with micromolar Ba²⁺ concentrations induced interictal-like events with duration and frequency that were lower than those observed with CCh; by contrast, the K_M blocker linopirdine was ineffective. Pre-treatment with Ba²⁺ or linopirdine increased the duration of epileptiform discharges induced by subsequent application of CCh. Baclofen, a GABA_B receptor agonist that activates K_IR, abolished CCh-induced field oscillations, an effect that was abrogated by the GABA_B receptor antagonist CGP 55845, and prevented by Ba²⁺. Finally, when applied after CCh, the K_M activators flupirtine and retigabine shifted leftward the cumulative distribution of CCh-induced event duration; this effect was opposite to what seen during linopirdine application under similar experimental conditions. Overall, our findings suggest that K_IR rather than K_M plays a major regulatory role in controlling CCh-induced epileptiform synchronization.