Postnatal development of voltage-gated K currents on rat sympathetic neurons.

1. We have investigated the developmental expression of three voltage-gated K currents on neonatal rat superior cervical ganglion (SCG) neurons in vivo and in culture: a rapidly inactivating current (IAf), a slowly inactivating current (IAs), and a noninactivating current (IK). 2. On postnatal day 1 neurons (P1), mean peak IAs is 67 +/- 4 (SE) pA/pF, peak IAf is 27 +/- 3 pA/pF, and IK is 14 +/- 3 pA/pF. Over the next wk, there is a switch in the expression of these currents: IAs drops by 40%, whereas IAf increases by greater than 100%; there is no change in IK. On P14 neurons, IAs is 38 +/- 2 pA/pF, IAf is 64 +/- 5 pA/pF, and IK is 12 +/- 1 pA/pF. 3. The change in expression of K currents on SCG neurons over the first 2 postnatal wk is unaffected by preganglionic innervation or by innervation of the targets. 4. To learn more about the factors that affect K current expression on these neurons, we grew SCG neurons in culture without other cell types for various times, and we measured the expression of IAf, IAs, and IK. In culture, the currents remained at their P1 levels for the first 4-7 days. Thereafter, both IAs and IAf decreased to low levels over a period of 2-3 wk. These results suggest that an epigenetic factor(s) is necessary for the expression of IAf and IAf in vivo and that this factor is missing in culture. 5. When IAs and IAf decreased on neurons in culture, we observed a compensatory increase in IK. After 4 wk in culture, IK is fourfold greater than on neurons in vivo. This result suggests that these neurons have intrinsic mechanisms that coordinate the expression of different voltage-gated K currents.     

Delayed rectifier potassium currents and Kv2.1 mRNA increase in hippocampal neurons of scopolamine-induced memory-deficient rats

To explore the ionic mechanisms of memory deficits induced by cholinergic lesion, whole-cell patch clamp recording techniques in combination with single-cell RT-PCR were used to characterize delayed rectifier potassium currents (IK) in acutely isolated hippocampal pyramidal neurons of scopolamine-induced cognitive impairment rats. Scopolamine could induce deficits in spatial memory of rats. The peak amplitude and current density of IK measured in hippocampal pyramidal neurons were increased from 1.2+/-0.6 nA and 38+/-19 pA/pF of the control group (n=12) to 1.8+/-0.5 nA and 62+/-24 pA/pF (n=48, P<0.01) of the scopolamine-treated group. The steady-state activation curve of IK was shifted about 8 mV (P<0.01) in the direction of hyperpolarization in scopolamine-treated rats. The mRNA level of Kv2.1 was increased (P<0.01) in the scopolamine-treated group, but there was no significant change of Kv1.5 mRNA level. The present study demonstrated for the first time that IK was enhanced significantly in hippocampal pyramidal neurons of scopolamine-induced cognitive impairment rats. The increase of Kv2.1 mRNA expression in hippocampal pyramidal cells might be responsible for the enhancement of IK and could be the ionic basis of the memory deficits induced by scopolamine.     

正常大鼠心室肌细胞钠、钙和钾离子流记录和特点

目的研究正常Sprague—Dawley大鼠外膜、中膜和内膜心室肌细胞钠离子电流（INa）、L-型钙离子电流（ICa-L）、瞬时外向钾离子电流（I60）、延迟整流性钾离子电流（IK）、内向整流性钾离子电流（IK1）的特点。方法采用酶消化法获得大鼠外膜、中膜和内膜心室肌细胞,以全细胞膜片钳技术记录心室肌细胞INa、ICa-L、Ito、IK和IK1。结果外膜至内膜心室肌细胞Ito电流密度逐渐减小,而外膜至内膜心室肌细胞INa、ICa-L、IK和IK1的电流密度无差异（P〉0．05）。结论大鼠心室肌细胞Ito存在分层差别,INa、ICa-L、IK和IK1不存在分层差别。     

牵张刺激对乳大鼠心房肌细胞瞬时外向钾电流和内向整流钾电流的影响

 目的：探究牵张刺激对乳鼠心房肌细胞瞬时外向钾电流（Ito）、内向整流钾电流（IK1）和动作电位时程（APD）的影响。方法：取1日龄SD乳大鼠心脏,分离、消化获得心房肌细胞。于细胞牵引装置培养24 h分组：对照组不予牵张刺激;牵张组予增加12%硅胶膜面积牵张刺激24 h。膜片钳全细胞记录方法记录细胞膜Ito、IK1和APD的变化。结果：在+60 mV刺激电压水平,牵张组Ito密度与对照组相比明显降低［(16±04）pA/pF vs (121±29) pA/pF,P<001］。在-120 mV刺激电压下,牵张组IK1密度较对照组增大［（-108± 08） pA/pF vs (-88±09)pA/pF,P<001］。牵张组动作电位复极50%（APD50）和复极90％（APD90）均较对照组明显缩短［(105±14）ms vs (155±24) ms,(300± 28) ms vs (563±36) ms,P<001］。结论：牵张刺激可降低乳大鼠心房肌细胞Ito密度,增大IK1密度,缩短APD,这可能是压力负荷增大致心房电重构的基础之一。     

An investigation of the role played by the E-4031-sensitive (rapid delayed rectifier) potassium current in isolated rabbit atrioventricular nodal and ventricular myocytes

The aim of this study was to measure and compare the profile of rapid delayed rectifier potassium current (IKr) elicited by action potential (AP) waveforms applied to isolated rabbit atrioventricular nodal (AVN) and ventricular myocytes. All measurements were made using whole-cell patch-clamp recordings at 37 degrees C. In AVN myocytes, IKr during voltage steps and slow ramp depolarisations showed "inward rectification" (characteristic for this channel) at positive potentials. The E-4031-sensitive current showed half-maximal activation at -10.8 +/- 0.86 mV, with a slope factor for the activation relation of 6.5 +/- 0.77 mV (n = 7). During AVN APs, IKr rapidly reached a peak after the AP upstroke and remained at similar amplitude until late in AP repolarisation. At the maximum diastolic potential following the AVN AP, a component of IKr remained which decayed during the pacemaker depolarisation, consistent with a role for the current in generating AVN pacemaker activity. In ventricular myocytes IKr was small at the beginning of the AP, and increased slowly during the AP plateau. Measurement of Ba-sensitive-inward rectifier K current (IK1) in ventricular myocytes revealed that IK1 rapidly increased during the final AP repolarisation phase, whilst IKr declined. It is concluded that IKr may participate in both AP repolarisation and the pacemaker depolarisation in AVN cells, whilst in ventricular myocytes, IKr and IK1 participate in controlling early and final AP repolarisation respectively.     

心房颤动患者内向整流性钾电流及Kir2.1 mRNA表达水平的研究

目的：研究心房颤动(房颤，AF)患者心房肌细胞内向整流性钾电流(Ik1)密度及Kir2.1(编码Ik1)mRNA表达水平，初步探讨慢性AF患者心房肌电生理重构机制。方法： 胶原酶Ⅱ两步酶解法分离心房肌细胞，膜片钳全细胞记录法记录离子电流；半定量逆转录聚合酶链反应方法检测心房组织Kir2.1 mRNA表达水平。结果： (1)AF患者心房肌细胞Ik1在超极化状态显著高于窦性心律(SR)组，在膜电位-120 mV时AF组Ik1增加34.04%(P＜0.05)，在-30 mV-+10 mV时其外向电流成分显著增加；(2)以GAPDH为内参标基因，AF组和SR组心房肌Kir2.1 mRNA相对表达量无显著差异(P＜0.05)。结论： AF患者右心房肌细胞Ik1密度在超极化状态显著增加是其电生理重构的重要离子基础之一；AF患者心房肌Kir2.1 mRNA表达水平无显著改变，推测Ik1重构为转录后调节。     

Effects of caffeine on potassium currents in isolated rat ventricular myocytes

Rapid exposure of cardiac muscle to high concentrations of caffeine releases Ca(2+) from the sarcoplasmic reticulum (SR). This Ca(2+) is then extruded from the cell by the Na(+)/Ca(2+) exchanger. Measurement of the current carried by the exchanger (I(Na/Ca)) can therefore be used to estimate of the Ca(2+) content of the SR. Previous studies have shown that caffeine, however, can also inhibit K(+) currents. We therefore investigated whether the inhibitory effects of caffeine on these currents could contaminate measurements of I(Na/Ca). Caffeine caused partial inhibition of the inward rectifier K(+) current (I(K1)): the outward current at -40 mV was 1.15+/-0.24 pA/pF in control and decreased to 0.34+/-0.15 pA/pF in the presence of 10 mmol/l caffeine (P<0.05, n=15). This was similar to the effect of caffeine on the holding current observed at -40 mV in the absence of K(+) channel block and could therefore account for the contaminating effects of caffeine observed during measurements of I(Na/Ca). Moreover, caffeine also partially inhibited the transient outward ( I(to)) and the delayed rectifier (I(K)) K(+) currents.     

BQ123对慢性缺氧大鼠肺动脉平滑肌细胞电压门控钾通道活性的影响

目的：探讨内皮素-1受体（ETA）拮抗剂BQ123对慢性缺氧大鼠肺动脉平滑肌细胞(PASMCs) 电压门控钾通道（KV）活性的影响。方法： 将12只Wistar大鼠随机分为对照组和慢性缺氧组，每组6只。用急性酶分离法（胶原酶+木瓜酶）获得单个PASMCs，用全细胞膜片钳记录方法，观察BQ123对2组大鼠PASMCs电压门控钾电流（IKV）的影响。结果：(1)在2组大鼠，ET-1（10-8 mol·L-1）对PASMCs IKV都可产生抑制作用，+50 mV时的抑制率分别是（60.21±5.32）%和 (71.04±6.58)%。(2)对照组大鼠，单独使用BQ123对PASMCs IKV无影响（P>0.05，n=5），在此基础上使用ET-1， ET-1对IKV的抑制作用依然存在。(3)慢性缺氧组大鼠，单独使用BQ123可增加PASMCs IKV，+50mV从（98.36±12.04）pA/pF至（105.76±12.13）pA/pF，但差异无显著（P>0.05，n=6），同时使用ET-1后发现BQ123可部分抵消ET-1对IKV的抑制作用，+50 mV从（28.49±6.69） pA/pF升至（74.19±9.74）pA/pF（P<0.01，n=6）。结论：常氧时，ET-1对IKV的抑制作用不是通过ETA介导的。但在缺氧条件下，ETA拮抗剂BQ123可部分拮抗ET-1对IKV的抑制作用，说明缺氧时ETA受体介导了ET-1对IKV抑制作用。     

Characteristics of a transient outward current (sensitive to 4-aminopyridine) in Ca2+-tolerant myocytes isolated from the rabbit atrioventricular node

 A transient outward current (I _to) has been observed in the atrioventricular node (AVN), but its characteristics in Ca-tolerant AVN myocytes have not been investigated previously. In this study, I _to was measured from Ca-tolerant rabbit AVN myocytes at 37°C, using the whole-cell patch-clamp technique. With interfering currents inhibited, 500-ms voltage-clamp pulses applied from –80 mV elicited I _to at potentials positive to –30 mV, which increased in magnitude with test potential amplitude. This current was completely blocked by external application of 5 mM 4-aminopyridine (4-AP). During a command pulse, I _to activated rapidly then inactivated with a bi-exponential time-course. Fast and slow time constants of current inactivation (τ_f and τ_s, respectively) showed voltage dependence. At 0 mV, τ_f was 14.5±2.7 ms and τ_s was 112.8±21.2 ms, whilst at +60 mV τ_f was 6.7±1.1 ms and τ_s was 63.7±9.2 ms (n=25). The steady-state inactivation relationship showed half-maximal inactivation at –33.8 mV (n=8). Re-activation of I _to after an inactivating pre-pulse showed a bi-exponential time-course of recovery: τ₁ was 196±70 ms, and τ₂ was 2707±1010 ms (n=6, at –80 mV). Repetitive application of voltage-clamp test pulses showed that I _to inactivation accumulated on repetitive stimulation, but reached a steady state rapidly for a given pulse frequency (0.2–1.0 Hz). AVN I _to was sensitive to the class 1 anti-arrhythmic flecainide (EC₅₀ for peak current of 24 μM), which showed selectivity for the rapidly inactivating current component. Quinidine also inhibited I _to in a dose-dependent fashion, but did not affect the current time-course. Under voltage-clamp conditions, a simulated diastolic depolarisation from –70 to –45 mV did not significantly reduce I _to amplitude, and under current-clamp conditions 4-AP inhibited spontaneous action potentials. Although this is consistent with a significant role for I _to in shaping AVN activity, under the conditions of this study 4-AP also partially blocked the ”rapid” delayed rectifier current, I _Kr, and so the effects of 4-AP on action potentials could not be attributed exclusively to its effects on I _to. Received: 22 October 1998 / Received after revision: 19 January 1999 / Accepted: 20 January 1999     

Voltage-gated calcium currents in axotomized adult rat cutaneous afferent neurons

The effect of sciatic nerve injury on the somatic expression of voltage-gated calcium currents in adult rat cutaneous afferent dorsal root ganglion (DRG) neurons identified via retrograde Fluoro-gold labeling was studied using whole cell patch-clamp techniques. Two weeks after a unilateral ligation and transection of the sciatic nerve, the L(4)-L(5) DRG were dissociated and barium currents were recorded from cells 3-10 h later. Cutaneous afferents (35-50 microm diam) were classified as type 1 (possessing only high-voltage-activated currents; HVA) or type 2 (having both high- and low-voltage-activated currents). Axotomy did not change the percentage of neurons exhibiting a type 2 phenotype or the properties of low-threshold T-type current found in type 2 neurons. However, in type 1 neurons the peak density of HVA current available at a holding potential of -60 mV was reduced in axotomized neurons (83.9 +/- 5.6 pA/pF, n = 53) as compared with control cells (108.7 +/- 6.9 pA/pF, n = 58, P < 0.01, unpaired t-test). A similar reduction was observed at more negative holding potentials, suggesting differences in steady-state inactivation are not responsible for the effect. Separation of the type 1 cells into different size classes indicates that the reduction in voltage-gated barium current occurs selectively in the larger (capacitance >80 pF) cutaneous afferents (control: 112.4 +/- 10.6 pA/pF, n = 30; ligated: 72.6 +/- 5.0 pA/pF, n = 36; P < 0.001); no change was observed in cells with capacitances of 45-80 pF. Isolation of the N- and P?Q-type components of the HVA current in the large neurons using omega-conotoxin GVIA and omega-agatoxin TK suggests a selective reduction in N-type barium current after nerve injury, as the density of omega-CgTx GVIA-sensitive current decreased from 56.9 +/- 6.6 pA/pF in control cells (n = 13) to 31.3 +/- 4.6 pA/pF in the ligated group (n = 12; P < 0.005). The HVA barium current of large cutaneous afferents also demonstrates a depolarizing shift in the voltage dependence of inactivation after axotomy. Injured type 1 cells exhibited faster inactivation kinetics than control neurons, although the rate of recovery from inactivation was similar in the two groups. The present results indicate that nerve injury leads to a reorganization of the HVA calcium current properties in a subset of cutaneous afferent neurons.     

Functional interaction of auxiliary subunits and synaptic proteins with Ca(v)1.3 may impart hair cell Ca2+ current properties

We assessed the functional determinants of the properties of L-type Ca(2+) currents in hair cells by co-expressing the pore-forming Ca(V)1.3alpha(1) subunit with the auxiliary subunits beta(1A) and/or alpha(2delta). Because Ca(2+) channels in hair cells are poised to interact with synaptic proteins, we also co-expressed the Ca(V)1.3alpha(1) subunit with syntaxin, vesicle-associated membrane protein (VAMP), and synaptosome associated protein of 25 kDa (SNAP25). Expression of the Ca(V)1.3alpha(1) subunit in human embryonic kidney cells (HEK 293) produced a dihydropyridine (DHP)-sensitive Ca(2+) current (peak current density -2.0 +/- 0.2 pA/pF; n = 11). Co-expression with beta(1A) and alpha(2delta) subunits enhanced the magnitude of the current (peak current density: Ca(V)1.3alpha(1) + beta(1A) = -4.3 +/- 0.8 pA/pF, n = 10; Ca(V)1.3alpha(1) + beta(1A) + alpha(2delta) = -4.1 +/- 0.6 pA/pF, n = 9) and produced a leftward shift of approximately 9 mV in the voltage-dependent activation of the currents. Furthermore, co-expression of Ca(V)1.3alpha(1) with syntaxin/VAMP/SNAP resulted in at least a twofold increase in the peak current density (-4.7 +/- 0.2 pA/pF; n = 11) and reduced the extent of inactivation of the Ca(2+) currents. Botulinum toxin, an inhibitor of syntaxin, accelerated the inactivation profile of Ca(2+) currents in hair cells. Immunocytochemical data also indicated that the Ca(2+) channels and syntaxin are co-localized in hair cells, suggesting there is functional interaction of the Ca(V)1.3alpha(1) with auxiliary subunits and synaptic proteins, that may contribute to the distinct properties of the DHP-sensitive channels in hair cells.     

柯萨奇B3病毒对心肌细胞钙平衡的影响

目的 探讨柯萨奇Ｂ３病毒（Ｃｏｘｓａｃｋｉｅｖｉｒｕｓ Ｂ３,ＣＶＢ３）对膜离子通道及离子交换载体的影响,了解病毒感染导致细胞内钙超载的原因。方法 酶灌注法获得单个心肌细胞后用光聚焦显微镜和钙离子荧光探针（Ｆｌｕｏ ３／ＡＭ）检测ＣＶＢ３感染对心肌细胞内游离钙离子浓度的影响及利用模片钳全细胞电流记录技术观察ＣＶＢ３对Ｌ型钙通道电流,钠通道电流和钠钙交换电流的影响。结果 ＣＶＢ３感染使细胞内的游离钙     

高胆固醇血症对大鼠心室肌细胞离子电流的作用

目的：观察高胆固醇血症对大鼠心室肌细胞离子电流的作用。方法： 通过全细胞膜片钳技术记录用酶解法分离的正常和高胆固醇饮食的大鼠心室肌细胞离子电流。结果： 高胆固醇组（组Ⅱ）血清总胆固醇水平明显高于正常组（组Ⅰ）［（3.10±0.62)mmol·L-1 vs (1.18±0.37)mmol·L-1, P<0.01, n=20］。组Ⅱ血清甘油三酯也明显高于组Ⅰ［（1.51±0.30)mmol·L-1 vs (0.43±0.15)mmol·L-1, P<0.01, n=20］。组Ⅱ大鼠心室肌细胞动作电位时程（APD）与组I相比明显延长，APD50从(70.86±8.12)ms延长至(116.16±6.90)ms (n=10, P<0.01); APD90 从(95.10±7.27)ms延长至(144.04±7.39)ms (n=10, P<0.01)；在实验电压 -120 mV， Ik1从(-16.98±4.54) pA/pF（组I）增加到(-19.92±4.08) pA/pF（组Ⅱ）(n=12, P<0.05)；在实验电压 0 mV， ICa-L从(-8.56±1.29) pA/pF（组Ⅰ）减少到(-5.24±0.90) pA/pF（组Ⅱ）(n=10, P<0.01)；在实验电压 +60 mV，Ito从(13.20±1.97) pA/pF（组I）减少到(10.30±1.97) pA/pF（组Ⅱ）(n=8, P<0.05)。结论： 高胆固醇血症可显著改变心肌细胞离子电流密度的大小，对心脏具有毒性作用。     

Sodium currents in isolated rat CA1 pyramidal and dentate granule neurones in the post-status epilepticus model of epilepsy

Status epilepticus (SE) was induced in the rat by long-lasting electrical stimulation of the hippocampus. After a latent period of 1 week, spontaneous seizures occurred which increased in frequency and severity in the following weeks, finally culminating after 3 months in a chronic epileptic state. In these animals we determined the properties of voltage-dependent sodium currents in acutely isolated CA1 pyramidal neurones and dentate granule cells using the whole-cell voltage-clamp technique. The conductance of the fast transient sodium current was larger in SE rats (84+/-7 nS versus 56+/-6 nS) but related to a difference in cell size so that the neurones had a similar specific sodium conductance (control: 7.8+/-0.8 nS/pF, SE: 6.7+/-0.8 nS/pF). Current activation and inactivation were characterised by a Boltzmann function. After SE the voltage dependence of activation was shifted to more negative potentials (control: -45.1+/-1.4 mV, SE: -51.5+/-2.9 mV, P<0.05). In combination with a small shift in the voltage dependence of inactivation to more depolarised potentials (control: -68.8+/-2.3 mV, SE: -66.3+/-2.3 mV), it resulted in a window current that was much increased in the SE neurones (median: 64 pA in control, 217 pA in SE, P<0.05). The peak of this window current shifted to more hyperpolarised potentials (control: -44 mV, SE: -50 mV, P<0.05). No differences were found in the sodium currents analysed in dentate granule cells of control and SE animals. The changes observed in CA1 neurones after SE contribute to enhanced excitability in particular when membrane potential is near firing threshold. They can, at least partly, explain the lower threshold for epileptic activity in SE animals. The comparison of CA1 with DG neurones in the same rats demonstrates a differential response in the two cell types that participated in very similar seizure activity.     

Regional distribution of potassium currents in the rabbit pulmonary arterial circulation

The response of pulmonary arteries to hypoxia varies as a function of vessel diameter. Small intrapulmonary resistance arteries are thought to be the main site of hypoxic pulmonary vasoconstriction (HPV), with hypoxia causing minimal contraction or even dilatation in large, conduit vessels. This has been proposed to reflect a differential distribution of morphologically and electrophysiologically distinct pulmonary artery smooth muscle (PASM) cells. We investigated longitudinal heterogeneity in smooth muscle cells isolated from five regions of the rabbit pulmonary vasculature and could find no evidence of morphological heterogeneity at the level of the light microscope. PASM cells from main (8 mm outer diameter) and branch (5 mm) arteries and large ( 400 m) intrapulmonary arteries (IPA) were similar in shape and size, as indicated by cell capacitance (25 pF). PASM cells from medium (200-400 m) and small ( 200 m) IPA were significantly smaller (15 pF), but had the same classical spindle shape. Cells from all five regions also had similar resting membrane potentials and displayed voltage-activated K+ currents of similar amplitude when recorded in standard physiological solution. Longitudinal heterogeneity in K+ current became apparent when tetraethylammonium ions (TEA; 10 mM) and glibenclamide (10 M) were added. The remaining delayed rectifier current (IK(V)) doubled in amplitude upon moving down the pulmonary arterial tree from the main artery (9 pA pF-1 at 40 mV) to the large IPA (17 pA pF-1), but remained constant throughout the intrapulmonary vasculature. The O2-sensitive, non-inactivating K+ current (IK(N)) showed a similar trend, but was significantly reduced in the smallest IPA, where its amplitude was comparable with the main artery. Thus the IK(N)/IK(V) ratio was relatively constant, at around 0.14, from the main pulmonary artery to medium IPA, but fell by 50% in the smallest vessels. The amplitude of the TEA-sensitive K+ current was similar (16 pA pF-1 at 40 mV) at all levels of the pulmonary arterial tree, except in the medium sized vessels where it was 50% smaller. These variations in K+ current expression correlate with reported variations in sensitivity to hypoxia and may contribute to the regional heterogeneity of HPV in the rabbit lung.     

Zacopride增强心肌内向整流钾电流(I_(K1))发挥抗心律失常效应

目的:探讨zacopride对乌头碱、氯化钡药物性心律失常模型的影响和增强心肌内向整流钾电流(IK1)与其抗心律失常的关系。方法:应用全细胞膜片钳技术观测zacopride对大鼠心室肌细胞膜主要离子流及静息膜电位(RMP)、动作电位(AP)和乌头碱所致延迟后除极(DAD)及触发活动(TA)的影响。并观察zacopride对乌头碱(30μg/kg,iv)和氯化钡(4 mg/kg,iv)2种药物性心律失常的影响。结果:0.1-10.0μmol/L zacopride可浓度依赖性激活大鼠心室肌IK1(P0.01),而对INa、Ito、ICa-L等影响动作电位的主要离子流均无显著影响(P0.05);使心室肌细胞膜超极化,动作电位时程(APD)缩短。1.0μmol/L为其最大效应浓度,使IK1内向电流部分(-100mV)增大33.8%,外向电流部分(-60 mV)增大32.4%;RMP由(-81.3±0.9)mV增大至(-87.5±1.7)mV,APD90由(32.48±2.70)ms缩短至(25.61±3.97)ms(P0.01),并有效消除乌头碱所致延迟后除极(DAD)和触发活动(TA)。对于乌头碱、氯化钡所致心律失常,15μg/kg zacopride可使2种心律失常持续时间分别由(57.58±3.21)min、(49.31±2.46)min缩短至(38.25±2.59)min和(30.94±1.73)min(P0.01)。结论:Zacopride对乌头碱、氯化钡药物性心律失常的抑制作用是由其激活心肌细胞IK1进而增大静息膜电位介导的。增强心室肌IK1可能成为抗心律失常的新机制。     

病毒感染大鼠心室肌细胞钙通道基因表达及功能改变的研究

目的：研究大鼠心室肌细胞感染柯萨奇病毒B3（CVB3）后L型钙通道mRNA表达量及其电生理特性的变化。 方法: 用CVB3感染培养的SD大鼠心室肌细胞，采用半定量逆转录-聚合酶链式反应技术，检测病毒感染心室肌细胞L型钙通道各亚单位mRNA表达量的变化；用全细胞膜片钳技术，观察病毒感染前后心室肌细胞L型钙电流（ICa-L）的变化。结果: 病毒感染组心室肌细胞L型钙通道α1和β亚单位mRNA的表达量显著高于正常对照组（4.00±0.07 vs 2.21±0.41, P<0.01; 2.06±0.06 vs 1.22±0.30, P<0.05），而α2/δ亚单位mRNA表达量的改变不明显（4.12±0.19 vs 4.13±0.27, P>0.05）；感染组细胞ICa-L的平均电流密度明显大于正常组细胞［（-8.66±0.99) pA/pF vs (-6.97±1.75) pA/pF, P<0.01］，且前者的电流-电压曲线下移，峰电流密度增加25.74%（P<0.05）。结论: CVB3感染心室肌细胞后，使其L型钙通道α1和β亚单位mRNA的表达量增加，ICa-L增大，可能是病毒感染导致心肌出现异常电生理活动的细胞和分子机制之一。     

内源性一氧化氮对哮喘大鼠支气管平滑肌细胞钾通道的影响

目的：观察体内应用一氧化氮（NO）前体左旋精氨酸（L-Arg）对哮喘大鼠支气管平滑肌细胞（BSMC）钾通道电生理特性的影响，为哮喘治疗提供理论基础。 方法： 雄性SD大鼠，随机分为对照组、哮喘组和哮喘L-Arg(300 mg/kg)治疗组（L-Arg组）。急性酶消化法分离获得大鼠单个BSMC。用常规全细胞膜片钳技术记录3组BSMC的静息膜电位（Em）、钙激活钾通道(BKCa)电流和电压依赖性钾通道（Kv）电流的差异。 结果： （1）哮喘组的静息膜电位为(-29.4±5.6) mV，显著低于对照组(-34.8±6.2)mV, (P<0.05)；L-Arg治疗组的静息膜电位为(-36.1±6.8) mV, 与哮喘组差异显著(P<0.05)。（2）钙激活钾通道电流：+50 mV电压刺激时，方波刺激模式下哮喘组大鼠BSMC的BKCa峰值电流密度［(43.8±16.5) pA/pF, n=8］低于对照组［(72.5±19.9)pA/pF, n=8］,(P<0.01)；L-Arg组的BKCa电流密度［(58.7±12.4) pA/pF, n=8］则高于哮喘组(P<0.05)。（3）电压依赖性钾通道电流：+50 mV电压刺激时，方波刺激模式下哮喘组大鼠BSMC的Kv峰值电流密度为［(32.4±8.7)pA/pF, n=8］，显著低于对照组［(57.7±9.8)pA/pF, n=8］ (P<0.01)；L-Arg组的Kv峰值电流密度［(43.6±7.9)pA/pF, n=8］，显著高于哮喘组［(32.4±8.7)pA/pF, n=8］ (P<0.05)。结论： 体内应用L-Arg可增加钙激活钾通道和电压依赖性钾通道电流，明显改善哮喘大鼠BSMC的静息膜电位，从而降低气道平滑肌细胞的兴奋性，可能具有抑制气道高反应性的作用。     

Voltage-dependent ionic currents in solitary horizontal cells isolated from cat retina.

1. Horizontal cells of the cat retina were isolated by enzymatic dissociation. Two types of horizontal cells were identified: the axonless (A-type) horizontal cell having four to six thick, long (approximately 100 microns) dendrites, and the short-axon (B-type) horizontal cell having many (> 5) fine, short (approximately 30 microns) dendrites. 2. Membrane properties of isolated horizontal cells were analyzed under current-clamp and voltage-clamp conditions. In the A-type cell, the average resting potential was -55 mV and the mean membrane capacitance was 110 pF, whereas values in the B-type cell were -58 mV and 40 pF, respectively. The A-type cell showed long-lasting Ca spikes, but B-type cells had no Ca spikes. 3. Five types of voltage-dependent ionic currents were recorded: a sodium current (INa), a calcium current (ICa), and three types of potassium currents. Potassium currents consisted of potassium current through the inward rectifier (Ianomal), transient outward potassium current (IA), and potassium current through the delayed rectifier (IK(v)). INa was recorded only from A-type cells. Other currents were recorded from both types of cells. 4. INa activated when cells were depolarized from a holding potential (Vh) of -95 mV, and it was maximal at -25 mV. This current was blocked by tetrodotoxin. Approximately half of the A-type cells had INa, but no B-type cell had this current. 5. L-type ICa, an inward-going sustained current, was activated with depolarization more positive than -25 mV. Current amplitude reached a maximal value near 15 mV and became smaller with further depolarization.(ABSTRACT TRUNCATED AT 250 WORDS)