心肌单细胞兴奋模式转迁的非线性动力学机理

利用Moms-Lecar模型研究实验观察到的培养心肌单细胞自发性兴奋模式转迁规律的动力学机理,确定性模型仿真,揭示了心肌单细胞随参数由“极化”静息经规则节律到“去极化”静息的节律变化规律。随机因素扰动下的模型仿真发现在分岔序列中的分岔点附近会出现含延迟后去极化电位、旱后去极化电位的节律模式,其中,延迟后去极化节律产生于从“极化”静息到规则节律的分岔点附近,而旱后去极化节律产生于从规则节律到“去极化”静息的分岔点附近。这表明含延迟后去极化电位的节律和含旱后去极化电位的节律是系统在自动兴奋和静息之间的分岔点附近由于参数的随机扰动而产生的。     

鳌虾口胃神经节神经元簇放电的动态离子流机制

为研究神经元自身的电活动特性(簇放电节律模式到峰放电节律模式的转迁,以及簇放电节律的离子流机制),本实验选取鳌虾口胃神经节(stomatogastric ganglion,STG)中功能上孤立的单个神经元,记录其在胞外钙离子浓度([Ca2+]o)变化和钙依赖钾离子通道阻断剂tetraethylammonium(TEA)作用下细胞内电活动的变化。当[Ca2+]o降低时,神经元膜电位水平升高,电活动模式表现为从低电位水平的静息(极化静息),到簇放电,再到峰放电,最后到高电位水平的静息(去极化静息)的转迁历程;当细胞外TEA浓度([TEA]o)增加时,神经元膜电位水平也升高,电活动模式表现为从极化静息,到簇放电,再到峰放电的转迁历程,且变化过程是可逆的。上述结果表明,不同生理状态下神经元电活动模式是复杂多样的,这种复杂多样的电活动模式随生理调节参数变化可以表现出规律性的转迁。另外,钙离子内流通过影响[Ca2+]i水平进而调节钙依赖钾电导,决定簇放电的起始与终止,这可能是簇放电产生的动态离子流机制。     

心肌细胞团搏动的整数倍节律的实验观察

实验报道了心肌细胞团自发性同步化搏动的一类新节律——整数倍节律。这种稳定的节律模式由两种相关的搏动形式的随机交替出现形成,这两种搏动形式中任何一种的出现间期具有整数倍特征。在静息状态和周期1搏动间的随机交替形成0-1整数倍节律,在周期1搏动和周期2搏动之间的随机交替形成l-2整数倍节律。0-1整数倍是居于静息状态和周期1节律之间的节律模式,1-2整数倍是居于周期1节律和周期2节律之间的节律模式,实验所见的节律转迁过程清楚地展示了静息状态、0-1整数倍节律、周期1节律、1-2整数倍节律、周期2节律等顺序地构成的一种“节律谱系”。“节律谱系”的观念可以为认识正常和异常心律的关系和其间的转迁机制提供深刻的理论启示。     

组胺致豚鼠心室乳头肌早发后去极化和触发活动的研究

采用微电极细胞内记录和电子计算机实时采样技术,研究了组胺致豚鼠心室乳头肌早发后去极化和触发活动。组胺(6.0μmol/L)可使动作电位APD_(50)、APD_(90)明显缩短(数据取自无异常自律性和振荡电位的细胞)。组胺可诱发早发后去极化(发生率57％),振荡电位和触发活动。早发后电位在低频驱动(0.2～1.0Hz)时易于发生且常常伴有动作电位时程的延长。触发活动可表现为快速自发性动作电位(发生率14％)。结果提示,组胺诱发的早发后去极化和触发活动可能和心性过敏反应等疾病发生的快速自律型心律失常有关。     

经长时间低温处理后由电刺激诱发的猪心室肌细胞持续性节律活动

用17个猪心研究了经长时(24-96小时)低温处理后,心室肌由电刺激诱发的节律性电活动。经48小时以上冷藏后,心室肌静息电位只有-20mV。单纯复温很难使静息电位增高.施与连续电刺激(1次/秒)时,心室肌标本中有些部分可发生局部反应。局部反应随时间而增大,同时静息电位也随之增高,并可出现可传播的动作电位。这种电位的特点是在复极化后有明显的超极化现象。在超极化不断加深后可产生后去极化。后去极化的不断增高达到一定程度时,就突然诱发出持续性节律活动.最初呈低电位节律活动,其动作电位呈慢反应型.最大舒张期电位(E_(max))为-52±3mV,动作电位总幅度(E_t)为55±7mV,dv/dt_(max)在10v/sec以下.这种节律活动频率较快并匀齐,可持续数小时之久.低电位自发节律有向高电位节律活动转变的倾向。高电位节律活动可由低电位节律演变而来,也可在较短时冷藏(24-48小时)后,由电刺激直接诱发产生。其主要条件是静息电位较大(负于—60mV).高电位节律活动是快反应型动作电位,E_(max)为—62±19mV,E_t为81±23mV,dv/dt_(max)在40V/sec与90V/sec之间。当动作电位超过90mV以上时,节律缓慢而不匀齐。有时在动作电位超过100mV或更高时,超极化及后去极化均消失,而皇“正常”心室肌动作电位图形。     

小鼠心室肌细胞内向整流钾电流的特性及其与早后去极化的关系

用全细胞膜片钳技术首次研究了成年小鼠单个心室肌细胞内向整流钾电流(I_k1)的整流特性,膜电导和反转电位对胞外钾离子浓度的敏感性及激活、失活动力学等性质。发现小鼠心室肌细胞I_k1最突出的特点就是其电压-电流(I～V)曲线在正于反转电位50mV的范围内无负斜率(negative slope)区,而是保持在一个很低的外向电流水平(59±39)pA。当用3mmol/L K^±和3mmol/L Cs^±灌流时,这一部分的I_k1减小为零,随后产生早后去极化(EAD)。结果提示:小鼠I_k1的这一特点与其EAD易发有关,I_k1受抑是本实验EAD发生的先决条件。     

棉铃虫成虫复眼的光谱敏感性及超极化后电位的研究

采用胞内记录方法研究了雄性棉铃虫小网膜细胞对光刺激的反应特性。结果如下：（１）小网膜细胞对５６２ｎｍ的光最敏感,另外对４００ｎｍ、４８３ｎｍ光也较敏感;（２）对这三种敏感光的光强度反应曲线（Ｖ／ＬｏｇＩｃｕｒｖｅ）与对白光的类似,在一定范围内,随光强度的增加反应增大,呈近似“Ｓ”形曲线;（３）超极化后电位的幅值随闪光刺激强度的增大、刺激时程的延长、对刺激光的敏感程度的增加而增大;（４）感受器的去极化电位与超极化后电位的比值不受刺激强度及光谱的影响,但随闪光刺激时程的延长而逐渐减小。     

非洲爪蟾顶盖神经元的抑制性微突触后电流频率和振幅的电压依赖性

采用全细胞记录膜片钳技术,研究非洲爪蟾脑片视顶盖神经元微突触后电流（miniature inhibitory postsynaptic current,mIPSC）频率和振幅对电压依赖关系。观察到以下结果：（1）当通过改变记录电极内的DC电流,将神经元的膜电位从静息电位逐步（每步10mV的增量）去极化或超极化时,mIPSC的频率和,或振幅分别升高或降低。随着膜电位的去极化,mIPSC的频率逐渐升高;当钳位电压升至＋10mV时,mIPSC的频率达到最高值。（2）当神经元去极化时,振幅仅轻微升高。膜电位去极化达到-30mV或-40mV时,mIPSC的振幅最大：进一步去极化,振幅反而下降。另外,在膜电位去极化至-20mV和＋10mV之间时,可记录到大的mIPSC。（3）在无Ca^2＋浸浴液中,mIPSC的频率和振幅也随膜电位的去极化而逐步增高,但频率的增高幅度远不如在生理盐水浸浴中增高幅度明显。（4）当浸浴液中[K＋]0增高时,mIPSC的频率明显降低,而振幅轻微降低。当细胞外[K^＋]。浓度升高超过20mmol／L时,神经元产生明显的缓慢内向或外向膜电流。mIPSC频率和振幅与膜电位存在依赖性的可能机制在文中作了简短的讨论。     

兔肠系膜下神经节细胞的两种非胆碱能性慢突触后电位

以常规细胞内记录技术对兔肠系膜下神经节细胞的跨膜电位进行了观察。对节前神经的短串脉冲刺激,可诱发出一串快兴奋性突触后电位(f-EPSP)或顺向动作电位;在此之后,大多数细胞还出现一个持续约2min 的缓慢去极化电位。该电位具有抗箭毒和阿托品性质,受低钙高镁溶液的可逆性阻抑,因而可称为非胆碱能性兴奋性突触后电位,或者也可归入迟慢兴奋性突触后电位(ls-EPSP)。多数细胞的 ls-EPSP 伴有膜电阻增大,电位的幅度随细胞静息电位的超极化而变小;提示在这些细胞上,钾电导的失活很可能参与了电位的发生。以P物质溶液灌流神经节未见该电位有显著改变。另外,在箭毒化加阿托品化的神经节中,还发现少数细胞对节前神经的串刺激发生一个持续约一分钟的超极化电位。它也具有抗胆碱能受体阻断剂的性质,受低钙高镁溶液可逆性阻抑,为此我们命之为“极慢抑制性突触后电位”(vs-IPSP),以区别于“慢抑制性突触后电位”(s-IPSP),后者是通常用以表示一种胆碱能性的慢电位。本文所述的这两种非胆碱能性的突触电位有关递质,尚待探索。     

豚鼠耳蜗外毛细胞的急性分离及钾离子通道的研究

本文对豚鼠耳蜗离体外毛细胞的细胞活性及底侧膜处电压依赖性钾离子通道进行了研究,结果表明：（１）离体外毛细胞悬液保存在４℃时,可延长存活时间达７ｈ以上。（２）外毛细胞的静息电位：应用电流钳方法,在刚形成全细胞方式时其细胞内静息电位为－７３．７±６．９ｍＶ,２ｍｉｎ后为－９４．８±４．１ｍＶ（ｘ±ｓ,ｎ＝１０）。（３）全细胞方式记录到的电压依赖性外向Ｋ＋电流是由快钾电流和延迟整流钾电流两部分组成,快钾电流的激活电位为－６０～－５０ｍＶ,延迟整流钾电流的激活电位为－４０～－３０ｍＶ,电流－电压关系曲线呈“Ｓ形上升”趋势。外向Ｋ＋电流被ＴＥＡ（２０ｍｍｏｌ／Ｌ）阻断后,可观察到一种电压依赖性内向电流     

Characteristics of the inward-rectifying potassium current in mouse ventricular myocytes and its relation to early after-depolarization

The properties of the inward-rectifying potassium current (IK1) were studied in the single myocytes isolated from adult mouse ventricles by the whole-cell patch-damp technique for the first time. Most of the properties of IK1 including channel conductances, activation, inactivation, rectification and external K sensitivity in mouse ventricular myocyte were similar to those in other species, but the current-voltage (1-V) curve of mouse ventricular myocyte showed no negative slope, i.e the slope in the range of membrane potential 50 mV positive to the reversal potential (VRev) was virtually flat and remained at a low current level ((59±39) pA). Under the superfusion of Tyrode's solution with 3mmol/L K and 3mmol/L Cs , IK1 in the above region nearly decreased to zero, and then the early after-depolarization (EAD) occurred. The results suggest that this distinctive characteristic of IK1 in mouse ventricular myocyte may relate to the high susceptibility to EA0 in mouse myocardium. The inhibition of IK1 se     

The state transition mechanism—simply depending on light-on and -off in Spirulina platensis

The state transition in cyanobacteria is a long-discussed topic of how the photosynthetic machine regulates the excitation energy distribution in balance between the two photosystems. In the current work, whether the state transition is realized by “mobile phycobilisome (PBS)” or “energy spillover” has been clearly answered by monitoring the spectral responses of the intact cells of the cyanobacterium Spirulina platensis. Firstly, light-induced state transition depends completely on a movement of PBSs toward PSI or PSII while the redox-induced one on not only the “mobile PBS” but also an “energy spillover”. Secondly, the “energy spillover” is triggered by dissociation of PSI trimers into the monomers which specially occurs under a case from light to dark, while the PSI monomers will re-aggregate into the trimers under a case from dark to light, i.e., the PSI oligomerization is reversibly regulated by light switch on and off. Thirdly, PSI oligomerization is regulated by the local H⁺ concentration on the cytosol side of the thylakoid membranes, which in turn is regulated by light switch on and off. Fourthly, PSI oligomerization change is the only mechanism for the “energy spillover”. Thus, it can be concluded that the “mobile PBS” is a common rule for light-induced state transition while the “energy spillover” is only a special case when dark condition is involved.     

Electrical activity and metabolism in cardiac tissue: An experimental and theoretical study

Summary (1) Effects of the metabolic inhibitor 2,4-dinitrophenol (DNP) on electrical activity in frog atria were studied by means of the sucrose-gap technique and in tracer experiments. (2) Voltage-clamp studies of ionic membrane currents showed a suppression by DNP of peak Na inward current without marked changes in the kinetics of the Na-carrying system and an increase of steady state outward current to three to five times its normal value. In⁴²K tracer experiments, DNP increased K resting efflux by about 10% and decreased K influx by 25 to 30%. (3) The depression of Na inward current is regarded as being caused by a partial block of Na channels and an increase of internal Na concentration after inhibition of active Na extrusion. (4) The strong rise in outward current is probably not caused by a K current since K efflux fails to show a correspondingly large change. As a possible explanation for current and flux changes, an electrogenic K pump is discussed. (5) A mathematical model of a carrier system transporting a single ion species is described. The system is designed as a direct potential pump. Uphill transport requires an asymmetry of the rate constants governing the cyclic formation and breakdown of carrier-ion complex. The asymmetry is brought about by an input of metabolic energy. Reduction of energy input decreases the asymmetry and induces a carrier-mediated downhill ion movement, with corresponding changes in membrane current and ion fluxes. (6) A model of electrogenic K inward transport is calculated that approximately accounts for the steady state current and the K flux changes experimentally observed after inhibition.     

Effects of conditioning polarization on the membrane ionic currents in rat myometrium

Summary Membrane ionic currents were measured in pregnant rat uterine smooth muscle under voltage clamp conditions by utilizing the double sucrose gap method, and the effects of conditioning pre-pulses on these currents were investigated. With depolarizing pulses, the early inward current was followed by a late outward current. Cobalt (1mm) abolished the inward current and did not affect the late outward currentper se, but produced changes in the current pattern, suggesting that the inward current overlaps with the initial part of the late outward current. After correction for this overlap, the inward current reached its maximum at about +10 mV and its reversal potential was estimated to be +62 mV. Tetraethylammonium (TEA) suppressed the outward currents and increased the apparent inward current. The increase in the inward current by TEA thus could be due to a suppression of the outward current. The reversal potential for the outward current was estimated to be –87 mV. Conditioning depolarization and hyperpolarization both produced a decrease in the inward current. Complete depolarization block occurred at a membrane potential of –20 mV. Conditioning hyperpolarization experiments in the presence of cobalt and/or TEA revealed that the decrease in the inward current caused by conditioning hyperpolarization was a result of an increase in the outward current overlapping with the inward current. It appears that a part of the potassium channel population is inactivated at the resting membrane potential and that this inactivation is removed by hyperpolarization.     

Electric currents in Xenopus tadpole tail regeneration

Xenopus laevis tadpoles can regenerate tail, including spinal cord, after partial amputation, but lose this ability during a specific period around stage 45. They regain this ability after stage 45. What happens during this “refractory period” might hold the key to spinal cord regeneration. We hypothesize that electric currents at amputated stumps play significant roles in tail regeneration. We measured electric current at tail stumps following amputation at different developmental stages. Amputation induced large outward currents leaving the stump. In regenerating stumps of stage 40 tadpoles, a remarkable reversal of the current direction occurred around 12-24 h post-amputation, while non-regenerating stumps of stage 45 tadpole maintained outward currents. This reversal of electric current at tail stumps correlates with whether tails regenerate or not (regenerating stage 40—inward current; non-regenerating stage 45—outward current). Reduction of tail stump current using sodium-free solution decreased the rate of regeneration and percentage regeneration. Fin punch wounds healed normally at stages 45 and 48, and in sodium-free solution, suggesting that the absence of tail re-growth at stage 45 is regeneration-specific rather than a general inhibition of wound healing. These data suggest that electric signals might be one of the key players regulating regeneration.     

Current- and Voltage-Clamped Studies on Myxicola Giant Axons : Effect of tetrodotoxin

A new dissection procedure for preparing Myxicola giant axons for observation under voltage clamp is described. Preparation time is generally 40–45 min. 65–70% of the preparations attempted may be brought through the entire procedure, including insertion of the long internal electrode, and support an initial action potential amplitude of 100 mv or greater. Mean values for axon diameter, resting membrane potential, action potential amplitude, maximum peak inward transient current, and resting membrane resistance are 560 µ, —66.5 mv, 112 mv, 0.87 ma/cm² and 1.22 KΩ cm ² respectively. Cut branches do not seem to be a problem in this preparation. Behavior under voltage clamp is reasonably stable over several hours. Reductions in maximum inward transient current of 10% and in steady-state current of 5–10% are expected in the absence of any particular treatment. Tetrodotoxin blocks the action potential and both the inward and outward transient current, but has no effect on either the resting membrane potential or the steady-state current. This selective action of tetrodotoxin on the transient current is taken as an indication that this current component is probably carried by Na.     

Two Fast Transient Current Components during Voltage Clamp on Snail Neurons

Voltage clamp currents from medium sized ganglion cells of Helix pomatia have a fast transient outward current component in addition to the usually observed inward and outward currents. This component is inactivated at normal resting potential. The current, which is carried by K+ ions, may surpass leakage currents by a factor of 100 after inactivation has been removed by hyperpolarizing conditioning pulses. Its kinetics are similar to those of the inward current, except that it has a longer time constant of inactivation. It has a threshold close to resting potential. This additional component is also present in giant cells, where however, it is less prominent. Pacemaker activity is controlled by this current. It was found that inward currents have a slow inactivating process in addition to a fast, Hodgkin-Huxley type inactivation. The time constants of the slow process are similar to those of slow outward current inactivation.     

Circadian aspects of body temperature regulation in exercise

Internal and external factors contribute to resting core temperature and affect thermoregulation. Also, a robust circadian rhythm exists, implying that the body is in “heat-gain” or “heat-loss” modes at different times during the 24 h. Moreover, many variables associated with exercise, and the body's capacity for exercise, show circadian variation. All these factors contribute to circadian changes in thermoregulation during exercise. Attention is focused on responses at the onset of exercise, “critical temperature”, and recovery after exercise. Practical implications of circadian changes in thermoregulation during exercise include ergogenic aids and inter-individual differences, including those due to gender, age and acclimatisation.