钡对培养的鼠心肌细胞动作电位与搏动的影响

本实验在培养的鼠心肌细胞上观察到:在无钡培养基中,心肌细胞可因膜超极化而使动作电位发放及自发性搏动停止;向培养基中加入0.1mMBaCl_2所致的除极化足以使此停搏的心肌细胞群落恢复搏动,并能使非搏动群落转化为搏动群落。当培养基中BaCl_2浓度在0.3—4.8mM范围内递增时,呈现剂量依赖性的搏动频率加快;动作电位的APA、OS、MDP、TP递减;APDbp、APDth、F递增,显著性由P<0.05递增至P<0.001。当BaCl_2浓度高于4.8mM时,又可因过度除极化而使动作电位及搏动骤停。上述实验所见完全符合钡离子阻塞钾通道,并可经钙通道内流、启动收缩的基本机制。     

在培养的心肌细胞中锌的抗氧自由基损伤作用的观察

本文通过向培养基中加入黄嘌呤和黄(?)呤氧化酶系统成分造成培养的心肌细胞受氧自由基伤害,以电生理的改变和BaCL_2引起心肌细胞停搏的闭浓度为指标,观察了微量元素Zn的抗氧化损伤作用。结果示:XOD组与对照组比较,动作电位APA、OS、MDP、TP、Vmax及APD_(50)各电参数明显减小。BaCl_2引起心肌细胞停搏的阈浓度亦减低。而加Zn组与对照组比较,以上结果除TP值偏低P<0.05外,其它参数则无显著性改变。加Zn组与XOD组相比,动作电位各电参数明显增大,BaCl_2引起心肌细胞停搏的阈浓度亦增高。提示Zn对培养的心肌细胞氧自由基所致的损伤具有保护作用。     

二乙酰吗啡干预离体乳鼠心肌细胞动作电位和钙离子电流的变化

文题释义：二乙酰吗啡：半合成的阿片受体纯激动剂,由吗啡和醋酸酐为原料经化学反应制成,其镇痛作用强于吗啡,镇痛效果为吗啡的4-8倍,其成瘾速度快,戒断难度大。长期使用后不仅会对人体的免疫功能造成严重破坏,还可导致心、肝、肾等重要脏器的功能损害。钙离子：作为细胞内第二信使,主要负责维持细胞膜正常电生理功能,以及确保机体多种生物信号转导途径正常进行。在心肌缺血缺氧过程中,当缺血引起心肌异常的L型钙电流逐渐恢复正常,钾通道活性程度降低,导致动作电位时程相对延长,L型钙电流在激活和失活的重叠区形成“窗流”,导致心肌细胞膜电位不稳而形成电震荡;当细胞内Ca2+大量积聚,增加 Ca2+-CaM复合物生成,心肌细胞易造成早期和晚期后除极,导致室性心律失常概率增加。 背景：阿片类药物可调控心肌细胞膜电位和Ca²⁺电流的变化,但是目前二乙酰吗啡是否诱导心肌节律、细胞动作电位和钙离子电流改变尚未见报道。 目的：探讨二乙酰吗啡对离体SD乳鼠心肌细胞动作电位和钙离子电流的影响。方法：①体外培养SD乳鼠心肌细胞,采用5个浓度二乙酰吗啡(0,10^-2,10^-3,10^-4,10^-5 mol/L)和20 mol/L维拉帕米作用于心肌细胞;②将细胞分为对照组、二乙酰吗啡组、二乙酰吗啡+维拉帕米组。后2组分别以二乙酰吗啡、二乙酰吗啡+维拉帕米(浓度20 μmol/L)联合干预心肌细胞;对照组加入等量PBS。实验于2018-05-21经新疆医科大学第一附属医院动物实验医学伦理委员会批准,批准号IACUC201805-K1。 结果与结论：①当不同浓度二乙酰吗啡干预心肌细胞24 h后,心肌细胞形态异常数量亦随其浓度的改变而明显增加,呈剂量依赖性改变。当二乙酰吗啡浓度逐渐升高,细胞存活数量亦逐渐减少,细胞胞质体积缩小,胞膜收缩,伪足减少,细胞核结构模糊。②与对照组相比,当加入二乙酰吗啡干预心肌细胞后,心肌细胞自发性搏动频率和节律差异有显著性意义。静息膜电位负值降低,动作电位中动作电位时程显著增加,动作电位幅度显著减小。③与对照组相比,二乙酰吗啡组中心肌膜电位改变数量明显增加,当加入维拉帕米后,心肌膜电位改变细胞数量有所降低。与对照组相比,心肌膜电位改变细胞数量有所升高。④提示二乙酰吗啡可致离体SD乳鼠心肌细胞形态异常,心肌自发性搏动频率和节律显著增加,心肌细胞膜电位和动作电位发生改变,钙通道阻滞剂维拉帕米对二乙酰吗啡引起的心肌细胞节律异常有一定改善作用。  ORCID: 0000-0002-5113-6050(苏丽萍) 中国组织工程研究杂志出版内容重点：组织构建;骨细胞;软骨细胞;细胞培养;成纤维细胞;血管内皮细胞;骨质疏松;组织工程     

沉默bim的表达对缺氧所致大鼠心肌细胞凋亡的影响

 目的：探讨唯BH3域蛋白Bim(Bcl-2 interacting mediator of cell  death)在缺氧所致大鼠心肌细胞凋亡中的作用。方法：在体外原代培养出生1~3 d的大鼠心肌细胞,并用抗α-横纹肌肌动蛋白免疫组化法进行鉴定。设计并化学合成3对靶向bim的siRNA,用脂质体法将siRNA转染心肌细胞,筛选沉默效率最高的siRNA。实验分组：（1）正常对照组;（2）缺氧组;（3）缺氧+脂质体组;(4)缺氧+阴性对照siRNA组;(5)缺氧+bim-siRNA组。倒置显微镜下观察心肌细胞的搏动频率和节律。全自动生化分析术检测细胞培养液中乳酸脱氢酶(LDH)的含量,用MTT法测定心肌细胞的存活率,流式细胞仪检测细胞凋亡率。Western blotting 检测细胞Bim、 Bax、Bcl-2和p-p38 MAPK和p38 MAPK蛋白的表达。结果：免疫组化鉴定证实大鼠心肌细胞原代培养成功。bim-siRNA转染均能有效沉默bim基因的表达（P<0.01）,其中第2对沉默效率最高,达到86.73%。缺氧使心肌细胞的搏动频率显著减慢,节律不规则,而沉默bim基因的表达能使细胞搏动频率增加。缺氧损伤导致细胞培养液中LDH含量较空白对照组明显增加（P<0.01）,心肌细胞存活率明显下降（P<0.05）,细胞凋亡率较空白对照组明显增加（P<0.01）,转染bim-siRNA后细胞培养液中LDH含量显著减少,细胞存活率升高,细胞凋亡率下降。缺氧损伤导致心肌细胞Bax和p-p38 MAPK表达升高（P<0.05或P<0.01）,Bcl-2蛋白表达下降（P<0.01）,bim-siRNA的转染能够抑制缺氧导致的上述改变（P<0.01或P<0.05）,并且与心肌细胞凋亡发生率降低一致,p38 MAPK表达无明显变化。结论：沉默bim的表达能有效抑制缺氧导致心肌细胞凋亡的作用,其机制可能与抑制Bax、p-p38 MAPK的表达和增强Bcl-2蛋白表达有关,这有望为冠心病的治疗提供新方向。     

盐酸克伦特罗对人类诱导多能干细胞来源心肌细胞的毒性作用

目的:探讨盐酸克伦特罗对人类诱导多能干细胞(iPSC)来源心肌细胞的毒性作用。方法:将人皮肤来源的iPSC成功定向分化为心肌细胞,加入不同浓度盐酸克伦特罗,使之分为对照组(0μg/ml)、1μg/ml组、10μg/ml组、20μg/ml组、50μg/ml组、100μg/ml组等6组(n均=3),相同条件共培养7天后,观察盐酸克伦特罗对心肌细胞形态大小、搏动频率及凋亡率的影响。结果:不同浓度盐酸克伦特罗均可使心肌细胞缩小(P0.05),50-100μg/ml盐酸克伦特罗可致心肌细胞骨架断裂,甚至呈颗粒状。各种浓度盐酸克伦特罗均致心肌细胞搏动频率加快(P0.05),且有浓度越高搏动越快的趋势。10μg/ml组和50μg/ml组所致心肌细胞凋亡率显著高于对照组(P0.05)。结论:盐酸克伦特罗对人类皮肤来源iPSC分化的心肌细胞有毒性作用。     

钼对大鼠心室肌细胞动作电位的影响

用克山病区粮(低Se)、非病区粮加W、病区粮加Mo喂养大鼠,分别复制低Se、低Mo及低Se高Mo的动物模型。病区粮组血Se浓度低于对照组(P<0.001);非病区粮加W组血Mo浓度低于对照组(P<0.001);病区粮加Mo组血Se浓度低于对照组(P<0.001)而血Mo浓度高于对照组(P<0.001)。采用浮置微电极技术,观察各组动物在体心肌细胞动作电位变化,结果显示;低Se与低Mo组APA均降低,且低Se加Mo组APA恢复正常,并使APD_(90)延长,提示Mo与Se对心肌细胞膜有类似功能。     

枸橼酸铁铵对原代培养的大鼠心肌细胞铜蓝蛋白、膜铁转运辅助蛋白和膜铁转运蛋白表达的影响

目的 观察枸橼酸铁铵(FAC)对原代培养的大鼠心肌细胞铁释放相关蛋白表达的影响,探讨枸橼酸铁铵对心肌细胞铁代谢的影响机制. 方法 以原代培养的乳鼠心肌细胞为材料,分为对照组、20mg/L枸橼酸铁铵组、40mg/L枸橼酸铁铵组和80mg/L枸橼酸铁铵组,每组6个重复.然后检测心肌细胞存活率、搏动频率,免疫组织化学检测铜蓝蛋白(CP)、膜铁转运辅助蛋白(HP)和膜铁转运蛋白(FP1)表达的变化. 结果 各剂量枸橼酸铁铵对大鼠心肌细胞存活率无明显影响;心肌细胞搏动频率减慢,停止跳动的细胞数量明显增加,收缩幅度逐渐降低;随着枸橼酸铁铵浓度的增加,心肌细胞铜蓝蛋白、膜铁转运辅助蛋白和膜铁转运蛋白的表达均增加. 结论 枸橼酸铁铵影响大鼠心肌细胞的生理功能,IRP-IRE可能参与膜铁转运蛋白表达的调控,铜蓝蛋白、膜铁转运辅助蛋白表达的升高可能与铁处理增加细胞的氧化紧张性有关.     

黄嘌呤-黄嘌呤氧化酶对培养心肌细胞的损伤及硒的保护作用

向培养心肌细胞中加入黄嘌呤-黄嘌呤氧化酶(X-XOD)后,动作电位的APA、OS、V_(max)及APD减少,MDP、TP水平上移;细胞在MEM中搏动率降低,加钡后细胞收缩频率迅速增加,且X-XOD作用时间越长,上述改变越显著。X-Mo的作用与此类似,但较轻。加硒则能逆转上述的细胞损伤性变化。这表明X-XOD和X-Mo均能造成心肌细胞损伤,硒对心肌细胞有保护作用。     

培养基中血清含量对培养心肌细胞的影响

用含有2％、5％、10％、20％血消的培养基培养大鼠心室肌细胞。降低培养基中的血清浓度使搏动群落在群落总数中所占的比值减少;抑制心肌细胞生长;使膜除极化、动作电位的阈电位、超射、波宽、波幅、最大除极速度减小。血清对培养心肌细胞的影响于培养早期更为明显。另外,本实验所用的两批血清之间也存在着显著差异。这些结果提示血清向培养的心肌细胞提供某些必需因素,而这些因素是人工合成的Eagle最低必需培养基所没有的,     

shRNA沉默 ROCK1和ROCK2 表达对缺氧诱导的大鼠心肌细胞凋亡的影响

目的: 探讨Rho相关的卷曲蛋白激酶(ROCK1)和ROCK2在缺氧诱导的大鼠心肌细胞凋亡中的作用。方法: 原代培养大鼠心肌细胞,并用抗α-横纹肌肌动蛋白免疫组化法进行鉴定。将ROCK1-shRNA和ROCK2-shRNA瞬时转染细胞,48 h后给予缺氧6 h处理。实验分为5组:(1)空白对照组;(2)缺氧组;(3)缺氧+阴性对照shRNA组;(4)缺氧+ROCK1-shRNA组;(5)缺氧+ROCK2-shRNA组。用倒置显微镜观察心肌细胞搏动频率与节律;用全自动生化分析仪测定细胞培养液中乳酸脱氢酶(LDH)含量;用MTT检测细胞存活率;用流式细胞仪检测细胞凋亡率;用Western blotting检测ROCK1和ROCK2的表达,并检测caspase-3和p-PI3K的表达情况。结果: 鉴定证实大鼠心肌细胞原代培养成功。缺氧损伤后心肌细胞搏动频率较对照组明显减慢,搏动幅度减弱,节律不规整(P<0.01),而ROCK1-shRNA和ROCK2-shRNA的转染能抑制缺氧导致的这一作用(P<0.05或P<0.01)。全自动生化分析仪检测发现,缺氧能导致细胞培养液LDH含量升高(P<0.01),而ROCK1-shRNA和ROCK2-shRNA的转染能抑制缺氧导致的这一作用(P<0.01)。MTT检测发现,缺氧能导致心肌细胞存活率降低(P<0.05),而ROCK1-shRNA和ROCK2-shRNA的转染能抑制缺氧导致的这一作用(P<0.05)。流式细胞仪检测发现,缺氧能导致心肌细胞凋亡率升高(P<0.01),而ROCK1-shRNA和ROCK2-shRNA的转染能抑制缺氧导致的这一作用(P<0.05或P<0.01)。Western blotting检测发现,ROCK1-shRNA的转染能降低ROCK1的表达(P<0.05), ROCK2-shRNA的转染能降低ROCK2的表达(P<0.01);缺氧能导致caspase-3表达升高(P<0.05)、p-PI3K表达降低(P<0.01),ROCK1-shRNA和ROCK2-shRNA的转染能抑制缺氧导致的这一作用(P<0.05或P<0.01)。结论: ROCK1和ROCK2表达下调能抑制缺氧损伤导致的大鼠心肌细胞凋亡,其机制与抑制caspase-3活化和增强p-PI3K的表达有关。     

一氧化氮对缺血再灌注豚鼠左心室流出道自律性电活动的影响

目的:研究一氧化氮(NO)对豚鼠左心室流出道自发电活动的影响及其对缺血/再灌注(I/R)时自发电活动改变的影响。方法:采用标准玻璃微电极细胞内电位记录技术观测外源性NO供体硝普钠(SNP)对豚鼠左心室流出道自发慢反应电位的影响及其对I/R时该电位改变的影响。结果:1、10、100μmol/L SNP呈浓度依赖性地导致4相自动除极速度(VDD)和自发放电频率(RPF)明显增加,但1 000μmol/L SNP的效应不明显。SNP呈浓度依赖性地导致最大舒张电位(MDP)绝对值和动作电位幅度(APA)增大,0相最大除极速度(Vmax)加快,复极50%和90%时间(APD50和APD90)缩短。缺血10 min组VDD和RPF明显减慢,APA和Vmax明显增大,APD50和APD90明显延长。与缺血10 min组相比,再灌注10 min组VDD和RPF明显加快,且常出现节律不齐,MDP绝对值和APA明显减小,APD50和APD90明显缩短。1、10、100μmol/L SNP再灌注时可明显改善缺血造成的VDD和RPF减慢以及再灌注造成的节律不齐,1 000μmol/L SNP的上述效应不明显。各浓度SNP再灌注时均可使缺血造成的APA和APD的改变恢复至对照组水平。结论:SNP可呈浓度依赖性地增加左心室流出道的自律性,并可明显改善I/R导致的自发慢反应电位的改变。     

腺苷对豚鼠左心室流出道自律细胞的电生理效应

目的 研究腺苷对豚鼠左心室流出道自律性电活动及其对肾上腺素、低氧和酸中毒电生理效应的影响.方法 采用玻璃微电极细胞内电位记录技术,分别观察腺苷对左心室流出道自发慢反应电位及对肾上腺素、低氧和酸中毒所致该电位改变的影响.结果 (1)10、50及100 μmol/L腺苷可呈剂量依赖性降低豚鼠左心室流出道自律细胞的电活动.(2)10 ixmol/L肾上腺素可明显提高左心室流出道的自律性,50μmol/L腺苷明显降低肾上腺素导致的该部位自律性升高.(3)低氧和酸中毒均可使该部位的自律性电活动明显降低,50μmol/L腺苷可使其自律性进一步降低.结论 腺苷对左心室流出道的自律性及肾上腺素、低氧和酸中毒导致的自律性异常有一定影响.     

Serotonin in the lateral geniculate.

Serotonin was introduced, by means of a fine cannula, into the lateral geniculate body of cats immobilized with Flaxedil and artificially ventilated, while the electrical activity at the point of injection was monitored by means of microelectrodes. Doses of 1.25 to 30 mug dissolved in 0.5 to 2.0 mul of saline produced, in 2-30 min, changes in electrical activity characteristic of synchronization: increase in the rhythmicity and in the amplitude of the spontaneous gross waves and increase in the clustering of the spontaneous neuronal action potentials. At the same time the activity of neurons which produced action potentials of high amplitudes was decreased, the activity of neurons which produced action potentials of low amplitudes was increased. Action potentials of different amplitudes were produced, in this case, by neurons of different types. Thus, in the lateral geniculate as in other thalamic nuclei studied in previous investigations, the synchronization of spontaneous activity seems to require the simultaneous excitation and inhibition of two different types of neurons. The action of serotonin on activity evoked by stimulation with brief flashes of light was limited to the decrease in the amplitude of the average gross response and the inhibition of only one type of neuron. This suggests that, in the lateral geniculate body, serotonin may be implicated in different ways in the different network structures responsible for the development of spontaneous as contrasted with evoked activity.     

Membrane properties of rat locus coeruleus neurones

Intracellular recordings were made from neurones in the locus coeruleus contained within a slice cut from rat pons and maintained in vitro. Most neurones fired action potentials spontaneously at frequencies of between 1 and 5 Hz; this did not arise from spontaneous synaptic input but appeared to result from endogenous properties of the membrane conductances. Under voltage clamp at potentials near threshold for action potential generation (? 55 mV) there was a persistent inward calcium current. This current became less with membrane hyperpolarization and was abolished at about ?70 mV. Two potassium currents were observed. The first had properties similar to that generally described as the “fast” potassium current (I_K,A); it flowed transiently (for about 200 ms) when the membrane potential passed from about ?65 to ?45 mV, and was blocked by 4-aminopyridine. The second was a calcium-activated potassium current (I_K,Ca); it flowed for several seconds following a burst of calcium action potentials. Spontaneous and evoked action potentials had both tetrodotoxin-sensitive and tetrodotoxin-resistant components. The latter was apparently due to calcium entry. The potential changes occurring during the spontaneous firing of locus coeruleus neurones could be reconstructed qualitatively from the ionic conductances observed. The membrane properties of the locus coeruleus neurones were remarkably uniform; however, about 5% of cells impaled within the region of the locus coeruleus were electrophysiologically distinct. These atypical cells had short duration action potentials, did not fire spontaneously and had large spontaneous depolarizing synaptic potentials.     

Differences in electrophysiological and contractile properties of mammalian cardiac tissues bathed in bicarbonate - and HEPES-buffered solutions

AIM: The aim of this study was to compare the action potential configuration, contractility, intracellular Ca2+ and H+ concentrations in mammalian cardiac tissues bathed with Krebs and Tyrode solutions at 37 degrees C. RESULTS: In Langendorff-perfused guinea-pig hearts, loaded with the fluorescent Ca2+-indicator Fura-2, or H+-sensitive dye carboxy-SNARF, shifts from Krebs to Tyrode solution caused intra-cellular acidification, increased diastolic pressure and [Ca2+]i, decreased systolic pressure and [Ca2+]i, leading to a reduction in the amplitude of [Ca2+]i transients and pulse pressure. Contractility was also depressed in canine ventricular trabeculae when transferred from Krebs to Tyrode solution. Shifts from Krebs to Tyrode solution increased the duration of action potentials in multicellular cardiac preparations excised from canine and rabbit hearts but not in isolated cardiomyocytes. All these changes in action potential morphology, contractility, [Ca2+]i and [H+]i were readily reversible by addition of 26 mmol L(-1) bicarbonate to Tyrode solution. Effects of dofetilide and CsCl, both blockers of the delayed rectifier K current, on action potential duration were compared in Krebs and Tyrode solutions. Dofetilide lengthened rabbit ventricular action potentials in a significantly greater extent in Tyrode than in Krebs solution. Exposure of canine Purkinje fibres to CsCl evoked early after depolarizations within 40 min in all preparations incubated with Tyrode solution, but not in those bathed with Krebs solution. CONCLUSION: It is concluded that the marked differences in action potential morphology, [Ca2+]i, [H+]i and contractility observed between preparations bathed with Krebs and Tyrode solutions are more likely attributable to differences in the intracellular buffering capacities of the two media.     

Simultaneous intracellular and focal extracellular recording of junction potentials and currents, and the time course of quantal transmitter action in rodent vas deferens

Simultaneous recordings were made of spontaneous excitatory junction potentials and the underlying spontaneous excitatory junction currents in guinea-pig and mouse vas deferens using adjacent intracellular and focal extracellular electrodes. Concurrent spontaneous excitatory junction potentials and spontaneous excitatory junction currents were observed in a small proportion of smooth muscle cells penetrated intracellularly within 50–200 μ of the extracellular electrode. These simultaneous events had identical variations in time course, indicating that they were caused by the same transmitter release event. Their amplitudes were not related. Concurrent spontaneous excitatory junction potentials and currents had identical durations, rise times and time constants of decay, showing that the spontaneous excitatory junction potential reflects the time course of quantal transmitter action. In contrast, spontaneous “discrete events” obtained by differentiating the rising phases of spontaneous excitatory junction potentials with respect to time were brief compared with the underlying currents. Excitatory junction potentials evoked by electrical stimulation of the hypogastric nerve were prolonged compared to the underlying excitatory junction currents. The peaks in the first time differential of individual excitatory junction potentials (evoked discrete events) were brief compared to corresponding excitatory junction currents.

It is concluded that at the neuroeffector junction of the rodent vas deferens the membrane potential response to a quantum of spontaneously released transmitter is a good estimate of the duration of transmitter action, in accordance with some of the predictions for three-dimensional syncytial tissues. The first time differential of the membrane potential, the “discrete event”, does not reflect the time course of spontaneous or evoked quantal transmitter action in these syncytial tissues.     

Role of nitric oxide in the contraction of circular muscle in the rat portal vein

The role of nitric oxide in the electrical and mechanical activities of the rat portal vein was examined in circular muscle preparations with intact endothelium that were isolated from the longitudinal muscle layer. In contrast to the longitudinal muscle preparation, the circular muscle preparation did not show spontaneous phasic contraction. Inhibition of nitric oxide synthesis by Nomega-nitro-L-arginine (L-NNA) induced a tonic contraction. The contraction was inhibited by L-arginine, sodium nitroprusside or nifedipine. L-NNA did not induce contraction in endothelium-damaged preparations. The membrane potential of smooth muscle cells recorded in endothelium-intact preparations showed sporadic action potentials. L-NNA increased the frequency of action potentials without changing the resting membrane potential. The action potentials were inhibited by nifedipine. In the presence of L-NNA, sodium nitroprusside decreased the frequency of the action potentials without changing the resting membrane potential. These results indicated that contraction of rat portal vein circular muscles is inhibited tonically by nitric oxide, at least partly through inhibition of electrical activity.     

Spontaneous action potentials initiate rhythmic intercellular calcium waves in immortalized hypothalamic (GT1-1) neurons.

GT1-1 cells exhibit spontaneous action potentials and transient increases in intracellular calcium concentration ([Ca2+]i) that occur in individual cells and as spatially propagated intercellular Ca2+ waves. In this study, simultaneous cell-attached patch-clamp recording of action currents (indicative of action potentials) and fluorescence imaging of [Ca2+]i revealed that Ca2+ transients in GT1-1 cells were preceded by a single action current or a burst of action currents. Action currents preceded Ca2+ transients in a similar pattern regardless of whether the Ca2+ transients were limited to the individual cell or occurred as part of an intercellular Ca2+ wave. Both the action currents and Ca2+ transients were abolished by 1 microM tetrodotoxin. Removal of extracellular Ca2+ abolished all spontaneous Ca2+ transients without inhibiting the firing of action currents. Nimodipine, which blocks L-type Ca2+ currents in GT1-1 cells, also abolished all spontaneous Ca2+ signaling. Delivery of small voltage steps to the patch pipette in the cell-attached configuration elicited action currents the latency to firing of which decreased with increasing amplitude of the voltage step. These results indicate that spontaneous intercellular Ca2+ waves are generated by a propagated depolarization, the firing of action potentials in individual cells, and the resulting influx of Ca2+ through L-type Ca2+ channels. These patterns of spontaneous activity may be important in driving the pulsatile release of GnRH from networks of cells.     

Mechanism of irregular firing of suprachiasmatic nucleus neurons in rat hypothalamic slices

The mechanisms of irregular firing of spontaneous action potentials in neurons from the rat suprachiasmatic nucleus (SCN) were studied in hypothalamic slices using cell-attached and whole cell recording. The firing pattern of spontaneous action potentials could be divided into regular and irregular, based on the interspike interval (ISI) histogram and the membrane potential trajectory between action potentials. Similar to previous studies, regular neurons had a firing rate about >3.5 Hz and irregular neurons typically fired about <3.5 Hz. The ISI of irregular-firing neurons was a linear function of the sum of inhibitory postsynaptic potentials (IPSPs) between action potentials. Bicuculline (10-30 microM) suppressed IPSPs and converted an irregular pattern to a more regular firing. Bicuculline also depolarized SCN neurons and induced bursting-like activity in some SCN neurons. Gabazine (20 microM), however, suppressed IPSPs without depolarization, and also converted irregular activity to regular firing. Thus GABAA receptor-mediated IPSPs appear responsible for irregular firing of SCN neurons in hypothalamic slices.