马桑内酯致痫大鼠海马神经细胞外Na+、K+活度的变化

目的和方法：应用Na⁺、K⁺选择性微电极检测马桑内酯致痫大鼠海马及海马脑片神经细胞外Na⁺、K⁺活度的改变。结果：海马内注射马桑内酯（5 μL,5×10^-4 mol/L）致痫大鼠30 s、1 min和2 min后,海马神经细胞外Na⁺活度分别低于对照组27.7 mmol/L、50.3 mmol/L和57.8 mmol/L,而K活度则分别高于对照组2.3 mmol/L、2.4 mmol/L和2.9 mmol/L（P<0.01）。3 min后,K⁺活度基本恢复至对照水平,而Na⁺活度仍持续低于对照水平（P<0.01）。海马脑片的实验结果与在体实验相似。结论：海马神经细胞处于癫痫状态时,存在Na⁺内流、K⁺外流现象。     

海马内微量注射硫酸镁对马桑内酯诱发大鼠痫样放电的影响

目的和方法:采用皮层应用或海马内注射马桑内酯的方法致痫大鼠,用钙离子选择性微电极检测了致痫动物皮层、海马细胞外Ca2+浓度的变化,观察了海马CA2区注射硫酸镁对致痫大鼠脑电图和皮层、海马诱发电位的影响.结果:马桑内酯致痫时,皮层、海马细胞外Ca2+浓度分别降低了0.61 mmol·L-1和0.74 mmol·L-1,海马内注射硫酸镁能明显地抑制致痫动物皮层、海马诱发电位和脑电图痫样放电.结论: 镁盐的上述作用可能与抑制Ca2+流入神经元内有关.     

ATP敏感钾通道在马桑内酯所致海马神经元癫痫样放电中的作用

目的：为了研究马桑内酯致痫时癫痫样放电与神经元内在兴奋性变化的关系。方法：实验采用大鼠海马脑片技术，细胞外微电极记录的方法，观察了ATP敏感钾通道激动剂腺苷对海马脑片CA1区细胞群体锋电位的作用。结果：腺苷对马桑内酯所致的成串癫痫样放电具有抑制作用。结论：ATP敏感的钾通道可能是马桑内酯致痫时神经元内在兴奋性增高的重要因素之一。     

点燃大鼠海马脑片CA_1区电活动的变化

实验选用80只SD雄性大鼠,随机分成两组,40只实验组大鼠肌肉注射阈下致惊厥量的马桑内酯(1.25mg/kg,隔日一次)进行点燃,40只对照组大鼠以等量的生理盐水肌肉注射。将点燃7天后的大鼠与相应的对照组间隔取材制备海马脑片。用细胞外记录场电位的方法观察了点燃大鼠海马脑片CA_1区电活动,目的在于探讨点燃大鼠点燃效应保留的机制。     

马桑内酯在大鼠海马脑片上引起的癫痫样放电活动

马桑内酯(Coriaria lactone CL)是从抗精神病中草药—马桑寄生中提取的有效成分,它具有致痫作用。目前,运用C1在整体动物身上建立急、慢性癫痫模型的实验已获成。为了进一步从细胞水平探讨C1的致痫作用及可能的电生理学机制,本实验采用离体海马脑片技术,在40例海马脑片标本上进行了以下研究:     

马桑内酯对大鼠海马神经元细胞内游离钙离子浓度的影响

以荧光探针Fluo-3/AM为胞浆内游离钙特异性指示剂,通过激光扫描共聚焦显微镜动态监测急性分离SD大鼠(出生后7～14 d)海马神经元细胞内游离钙离子浓度([Ca2 ]i)的变化情况,以了解钙离子及钙通道在癫痫发病中的作用,探讨马桑内酯(coriaria lactone, CL)调节神经细胞内钙稳态的机理.实验发现,CL能使急性分离大鼠海马神经元[Ca2 ]i增加;nifedipine和低浓度NiCl2虽可延迟,但不能完全阻断这种作用.除促使电压依赖的T-、L-型钙离子通道开放外,CL尚可通过其他途径增加海马神经元内[Ca2 ]i,改变细胞兴奋性而致痫.     

两类钙通道拮抗剂对缺氧大鼠海马脑片Ca2+/CaM PK Ⅱ 活性的影响

用离体孵育的大鼠海马脑片模型，研究了两类钙通道拮抗剂对缺氧海马脑片Ca2 /CaM PKⅡ活性的影响。结果如下：(1)缺氧30min导致大鼠海马脑片Ca2 /CaM PKⅡ活性降至对照组的16.4%；(2)100μmol/L氯胺酮可部分拮抗缺氧导致的酶活性下降，使之恢复至对照组的40.6%；(3)10μmol/L苄丙咯可使缺氧导致的酶活性下降恢复至对照组的35.8%；(4)15μmol/L苄丙咯和50μmol/L氯胺酮联合用药可产生协同作用，使缺氧导致的酶活性下降恢复至对照组的63.8%。由此得出结论：缺氧对海马脑片Ca2 /CaM PKⅡ活性的抑制作用与NMDA受体门控的钙通道和Na /Ca2 交换通道异常开放有关。     

姜黄素在HIV-1 gp120致海马突触可塑性损伤中的作用机制研究

<正>目的:观察姜黄素对gp120 V3环所致大鼠海马神经元突触可塑性损伤的作用及机制。方法:制备离体大鼠海马脑片,1mol/L姜黄素或10 mol/L尼莫地平单独或分别与1 nmol/L gp120 V3环共同作用于大鼠海马脑片1h后,采用细胞外微电极记录技术,分别记录Schaffer侧支-CA1区神经元的输入/输出曲线(input-output curve,I/O curve)、场兴奋性突触后电位(field-ex-     

Wortmannin通过抑制癫痫大鼠海马自噬活性发挥神经保护作用

目的:探讨癫痫大鼠海马自噬活性的变化及自噬抑制剂wortmannin(WM)对致痫大鼠海马神经元的保护作用。方法:实验大鼠分为对照组、致痫2 h、8 h、16 h、24 h、72 h组和WM干预组。应用HE染色和Nissl染色观察癫痫大鼠海马神经元损伤的变化。免疫印迹检测海马组织微管相关蛋白1轻链3(LC3)Ⅱ/LC3Ⅰ的比值作为自噬活性的指标。结果:LC3Ⅱ/LC3Ⅰ比值在大鼠癫痫发作2 h时开始升高,24 h达到高峰,持续升高至少72 h。致痫24 h时海马CA1区出现明显神经元损伤和丢失。WM干预组CA1区存活神经元数目(100.88±18.73)显著高于癫痫组(70.16±5.09)(P0.05),LC3Ⅱ/LC3Ⅰ的比值低于癫痫组(P0.05)。结论:癫痫发作导致的海马损伤时存在自噬激活现象;WM通过抑制自噬活性减轻癫痫发作所致的海马损伤,具有神经保护作用。     

自体脑外转道模式下青霉素致痫大鼠海马C-fos、C-jun表达的影响

观察在脑内置入引导电极接自体脑外肌肉组织对青霉素致痫大鼠行为学、脑电图(EEG)及海马C-fos、C-jun的表达,探讨其对大鼠痫性发作的影响。实验动物随机分为三组,每只6只,分别为致痫组(海马内微注射青霉素制备痫性发作模型)、脑电转道组(致痫灶置入引导电极并接自体脑外肌肉组织)及对照组(脑内置入引导电极,不致痫)。观察各组大鼠行为学、EEG变化并应用免疫组化方法检测海马C-fos、C-jun的表达。实验中观察到致痫组、脑电转道组大鼠痫性发作次数无显著差别;脑电转道组EEG放电次数较致痫组显著减少(P<0.05);4 h点脑电转道组注药侧海马CA3、CA1区C-fos、C-jun表达明显低于致痫组注药侧(P<0.05)。本实验证实了自体脑外转道模式下,引导电极置入减少了致痫大鼠痫性放电次数,下调了致痫大鼠海马C-fos、C-jun的表达。     

Effect of external potassium on the coupled sodium: Potassium transport ratio of axons

1. Resting membrane potential and the current-voltage relation were measured in crayfish giant axons bathed in various potassium solutions with and without ouabain. 2. Ouabain caused a depolarization of the membrane at each [K]o used but did not affect membrane resistance. 3. The ouabain-sensitive transport current was least (3 microamperemeter/cm2) in 0 mM [K]o and greatest (7 microamperemeter/cm2) in 16.2 and 21.6 mM [K]o. 4. The assumption was made an some indirect evidence presented that axons equilibrated in various potassium solutions maintain constant internal sodium and potassium concentrations for up to 3 h. 5. On the basis of this assumption, the apparent ratio of coupled Na : K transport was calculated. It was found to be least (-1.3/1) in 0 mM [K]o and to approach infinity in 16.2 and 21.6 mM [K]o. 6. The data indicate that the apparent variability of the Na : K exchange ratio likely represents an intrinsic property of the exchange mechanism and is less likely to be explained by a fixed-ratio coupled Na : K transport operating in parallel with electro-neutral Na : Na or K : K exchange.     

Acute effects of dehydration on sweat composition in men during prolonged exercise in the heat

AIM: To determine whether acute exercise-heat-induced dehydration affects sweat composition, eight males cycled for 2 h at 39.5 +/- 1.6% VO2peak on two separate occasions in a hot-humid environment (38.0 +/- 0.0 degrees C, 60.0 +/- 0.1% relative humidity). METHODS: During exercise, subjects ingested either no fluid (dehydration) or a 20 mmol L(-1) sodium chloride solution (euhydration). The volume of solution, calculated from whole-body sweat loss and determined in a familiarization trial, was ingested at 0 min and every 15 min thereafter. Venous blood was collected at 0, 60 and 120 min of exercise and sweat was aspirated from a patch located on the dominant forearm at 120 min. RESULTS: Following the 2-h cycling exercise, sweat [Na+] and [Cl-] was greater (P < 0.05) in the dehydration trial (Na+ 91.1 +/- 6.8 mmol L(-1); Cl- 73.3 +/- 3.5 mmol L(-1)) compared with the euhydration trial (Na+ 81.1 +/- 5.9 mmol L(-1); Cl- 68.5 +/- 3.3 mmol L(-1)). In addition, dehydration invoked a greater serum [Na+] (142.2 +/- 0.7 mmol L(-1); P < 0.05), [Cl-] (105.8 +/- 0.6 mmol L(-1); P < 0.05) and [K+] (5.27 +/- 0.2 mmol L(-1); P < 0.05) over the euhydration values for [Na+], [Cl-] and [K+], respectively (138.9 +/- 0.6, 102.9 +/- 0.5 and 4.88 +/- 0.1 mmol L(-1)). Plasma aldosterone was also significantly higher during exercise in the dehydration trial compared with the euhydration trial (53.8 +/- 3.8 vs. 40.0 +/- 4.3 ng dL(-1); P < 0.05). CONCLUSIONS: Acute exercise-heat stress without fluid replacement resulted in a greater sweat [Na+] and [Cl-] which was potentially related to greater extracellular fluid [Na+], plasma aldosterone or sympathetic nervous activity.     

Simulated seizures and spreading depression in a neuron model incorporating interstitial space and ion concentrations

Sustained inward currents in neuronal membranes underlie tonic-clonic seizure discharges and spreading depression (SD). It is not known whether these currents flow through abnormally operating physiological ion channels or through pathological pathways that are not normally present. We have now used the NEURON simulating environment of Hines, Moore, and Carnevale to model seizure discharges and SD. The geometry and electrotonic properties of the model neuron conformed to a hippocampal pyramidal cell. Voltage-controlled transient and persistent sodium currents (I(Na,T) and I(Na,P)), potassium currents (I(K,DR) and I(K,A)), and N-methyl-D-aspartate (NMDA) receptor-controlled currents (I(NMDA)), were inserted in the appropriate regions of the model cell. The neuron was surrounded by an interstitial space where extracellular potassium and sodium concentration ([K(+)](o) and [Na(+)](o)) could rise or fall. Changes in intra- and extracellular ion concentrations and the resulting shifts in the driving force for ionic currents were continuously computed based on the amount of current flowing through the membrane. A Na-K exchange pump operated to restore ion balances. In addition, extracellular potassium concentration, [K(+)](o), was also controlled by a "glial" uptake function. Parameters were chosen to resemble experimental data. As long as [K(+)](o) was kept within limits by the activity of the Na-K pump and the "glial" uptake, a depolarizing current pulse applied to the cell soma evoked repetitive firing that ceased when the stimulating current stopped. If, however, [K(+)](o) was allowed to rise, then a brief pulse provoked firing that outlasted the stimulus. At the termination of such a burst, the cell hyperpolarized and then slowly depolarized and another burst erupted without outside intervention. Such "clonic" bursting could continue indefinitely maintained by an interplay of the rise and fall of potassium and sodium concentrations with membrane currents and threshold levels. SD-like depolarization could be produced in two ways, 1) by a dendritic NMDA-controlled current. Glutamate was assumed to be released in response to rising [K(+)](o). And 2) by the persistent (i.e., slowly inactivating) Na-current, I(Na,P). When both I(NMDA) and I(Na,P) were present, the two acted synergistically. We conclude that epileptiform neuronal behavior and SD-like depolarization can be generated by the feedback of ion currents that change ion concentrations, which, in turn, influence ion currents and membrane potentials. The normal stability of brain function must depend on the efficient control of ion activities, especially that of [K(+)](o).     

Effect of external magnesium on intracellular free sodium: Na+ flux via Na+/Mg2+ antiport is masked by other Na+ transport systems in rat cardiac myocytes.

Mg2+ efflux from heart cells on a Na+/Mg2+ antiport has been postulated, but the Na+ flux component of the antiport has not been demonstrated. The study aimed to establish if the Na+ flux component could be measured by following changes in [Na+]i with SBFI during conditions known to reverse the antiport (5 mmol/L Mg2+(o), Na+(o)- & Ca2+(o)-free): and after minimising the activity of other Na+ transport pathways. Resting [Na+]i was 8 +/- 0.7 mmol/L (mean +/- S.E., n = 39 cells) in normal Tyrode's solution. [Na+]i decreased below the normal level in all cells (a decline of 4-5 mmol/L, n = 21) during perfusion with 5 mmol/L Mg2+(o) (Na+(o)- & Ca2+(o)-free). Controls using 1 mmol/L Mg2+(o) showed similar declines in [Na+]i, but the fall was greatest when Na+(o) was replaced by K+(o) (decline of 6 mmol/L) rather than the tetramethylammonium ion (TMA+). The rate of decrease in [Na+]i during perfusion with 5 mmol/L Mg2+(o) (Na+(o)- & Ca2+(o)-free) was slowed by 20 microM ouabain (n = 5) or by elevation of pHo to pH 9 (n = 7) so that [Na+]i remained close to the initial value. The decrease of [Na+]i was not affected by 10 microM imipramine (n = 15). These data suggest that the Na+ efflux component of the Na+/Mg2+ antiport is masked in Na+(o)- and Ca2+(o)-free conditions by other Na+(i) efflux pathways.     

The sensitivity of the sodium pump to external sodium

1. When red cells are incubated in potassium-free solutions, ouabain-sensitive sodium efflux is nearly absent with 5 mM-Na externally, but increases as the external sodium concentration is reduced from 5 mM to zero. This increase suggests that the transport mechanism is very sensitive to small amounts of sodium at the outside surface of the cell membrane. Further evidence for such sensitivity has been obtained from the effects of external sodium on the relation between potassium influx and external potassium concentration.2. With 5 mM-[K](o), potassium influx is rather insensitive to [Na](o) but at low potassium concentrations even low levels of sodium inhibit.3. With 140 mM-[Na](o) the potassium influx curve is S-shaped below 1 mM [K](o). At much lower sodium concentrations, the S-shaped region and the value of [K](o) for which potassium influx is half-maximal are both shifted progressively towards zero. At 10 muM-[Na](o), potassium influx is half maximal at 0.14 mM-[K](o) and the curve is close to a rectangular hyperbola down to 22 muM-[K](o); there seems to be a trace of inflexion at about 15 muM-[K](o).4. When [Na](o) is reduced from 5 mM to zero, removal of the inhibitory effect of external sodium ions on sodium: potassium exchange could lead to an increase in sodium efflux into nominally potassium-free solutions if these solutions did in fact contain traces of potassium. Such traces could arise by leakage from the cells, but, in a number of experiments, direct measurements showed that [K](o) was too low to account in this way for all of the observed ouabain-sensitive sodium efflux. A further reason for rejecting this explanation is that ouabain-sensitive potassium loss into nominally (Na+K)-free solutions was unaffected by adding 5 mM-Na. (A slight increase in ouabain-resistant loss was observed.)5. The ouabain-sensitive efflux of sodium into (Na+K)-free solutions therefore seems to represent a mode of behaviour of the transport mechanism distinct both from the sodium: potassium exchange that occurs under physiological conditions and from the sodium: sodium exchange that occurs in K-free, Na-rich media.     

Effects of external potassium concentrations on the cell sodium and potassium contents of isolated rat kidney tubules

The effects of 20 mol/l amiloride, 10 mol/l furosemide and 1 mmol/l ouabain on cell Na and K concentrations were investigated by flame microphotometry in isolated rat medullary collecting tubules and medullary thick ascending limbs (MCT and MAL) as a function of the external potassium concentration [K_e]. The results are expressed as Na and K concentrations per liter cell volume ([Na_c] and [K_c], mmol/l) and relative sodium content, [Na_c]/([Na_c]+[K_c]). From the experimental curves, [K_e]_1/2 is defined as the [K_e] value corresponding to half maximal exchange of K against Na in cells. When [K_e] was 5 mmol/l, the relative Na content was less than 15% in control and amiloride-treated MCT as well as in control and furosemide-treated MAL, and about 24% in ouabain-treated MCT and MAL. In MCT, relative cell Na content increased up to 90% or more when [K_e] was reduced from 2.5 to 0.25 mmol/l. [Ke]_1/2 was 0.55, 0.45 and 1.25 mmol/l for control, amiloride-treated and ouabain-treated MCT respectively. In MAL, similar increases in relative Na content were observed when [K_e] was reduced from 0.5 to 0.05 mmol/l. [K_e]_1/2 was 0.25, 0.10 and 1.75 mmol/l for control, furosemide-treated and ouabain-treated MAL respectively. When [K_e] was reduced from 5 to 1 mmol/l, [Na_c] dropped from 16.4 to 8.4 mmol/l (P<0.01) in control MAL. When [K_e] was 5 mmol/l, [Na_c] was lower in furosemide-treated MAL (7.8 mmol/l) than control MAL (P<0.01). At 1 mmol/l [K_e], [Na_c] was similar in both groups.These results are discussed in terms of the balance between the active and passive components of Na and K fluxes across apical and basolateral cell membranes. They indicate that a K-dependent passive Na entry process exists in the membranes of MAL cells but not of MCT cells. This process was proportionally more inhibited than the active Na pump when [K_e] was reduced from 5 to 1 mmol/l. In addition, it was found sensitive to furosemide. It presumably corresponds to the luminal 1 Na-1 K-2 Cl contransport mechanism known to exist in the thick ascending limb.     

An interaction between potassium and sodium in the smooth muscle of the guinea-pig taenia coli

1. The potassium content of the guinea-pig taenia coli was 72 m-mole K/kg fr. wt. after equilibration with normal Krebs-type solution at 35 degrees C in vitro.2. It fell to 13 m-mole K/kg fr. wt. when Ca(2+) and Mg(2+) were omitted from the bathing solution, but this fall was reversed in part when [Na(+)](o) was also reduced.3. The taeniae relaxed when Ca(2+) and Mg(2+) were omitted from the normal solution. However, they contracted if Na(+) was also omitted.4. Effects 2 and 3 may show some antagonism between sodium and divalent cations in smooth muscle.5. The extracellular space of the same muscles was measured with [(14)C]sorbitol. It was 440 ml./kg fr. wt. in normal solution.6. The uptake of (42)K was measured in the same muscles at the same time. An initial rapid exchange was followed within 2 min by a slow (half-time [unk] 50 min in normal solution) and presumably intracellular uptake of tracer.7. In normal solution the initial rapid phase of (42)K exchange corresponded to 3.0 m-mole K/kg fr. wt. A value of 2.6 m-mole K/kg fr. wt. would have been calculated from [K(+)](o) and the [(14)C]sorbitol space, and these estimates did not differ significantly.8. The [(14)C]sorbitol space fell slightly when [Ca(2+)](o), [Mg(2+)](o), and [Na(+)](o) were reduced, but the amount of rapidly exchanging potassium increased significantly reaching 4.6 m-mole K/kg fr. wt. in solutions from which Ca(2+), Mg(2+) and Na(+) were omitted. The [(14)C]sorbitol space only accounted for 2.4 m-mole K/kg fr. wt. under these conditions, a significantly smaller quantity.9. The observations have been interpreted on Wilbrandt & Koller's (1948) hypothesis that there may be a superficial anionic region in muscle cells. On this model the present results suggest that K(+) rather than Na(+) is favoured as a monovalent counter-cation in the taenia coli.     

Characteristics of sodium and potassium transport in the lung.

Freshly prepared lung slices were incubated in an oxygenated Krebs-Ringer bicarbonate medium for 90 min at 0.5 degrees C (chilling) followed by 60 min at 38 degrees C (rewarming). Fresh tissue cation contents (mean +/- SE) in mmol/kg dry wt were: sodium, 431 +/- 7; potassium, 416 +/- 10. After chilling, tissue sodium increased to 757 +/- 11 and potassium decreased to 113 +/- 6. Upon rewarming there was a net increase in tissue potassium of about 150 (mmol/kg dry wt) and a net decrease in tissue sodium of about 130. Tissue extrusion of sodium and reaccumulation of potassium observed at 37 degrees C were abolished when 1 mM ouabain, dinitrophenol, or iodoacetamide was added to the incubation medium. Similar results were obtained when the medium contained no potassium or when medium Na was replaced by choline. The data indicate the presence of active Na+-K+ transport in lung cells somewhat similar to that found in other mammalian tissue.     

Serum potassium and acid-base parameters in severe dialysis-associated hyperglycemia treated with insulin therapy

We analyzed the changes in serum potassium concentration ([K]) and acid-base parameters in 43 episodes of dialysis-associated hyperglycemia (serum glucose level > 33.3 mmol/L), 22 of which were characterized as diabetic ketoacidosis (DKA) and the remaining 21 as nonketotic hyperglycemia (NKH). All episodes were treated with insulin therapy only. Age, gender, initial and final serum values of glucose, sodium, chloride, tonicity and osmolality did not differ between DKA and NKH. At presentation, serum values of [K] (DKA 6.2 +/- 1.3 mmol/L; NKH 5.2 +/- 1.5 mmol/L) and anion gap [AG] (DKA 27.2 +/- 6.4 mEq/L; NKH 15.4 +/- 3.5 mEq/L) were higher in DKA, whereas serum total carbon dioxide content [TCO2 ] (DKA 12.0 +/- 4.6 mmol/L; NKH 22.5 +/- 3.1 mmol/L), arterial blood pH (DKA 7.15 +/- 0.09; NKH 7.43 +/- 0.07) and arterial blood PaCO2 (DKA 26.2 +/- 12.3 mm Hg; NKH 34.5 +/- 6.7 mm Hg) were higher in NKH. At the end of insulin treatment, serum values of [K] (DKA 4.0 +/- 0.7 mmol/L, NKH 4.0 +/- 0.5 mmol/L), [AG] (DKA 16.3 +/- 5.4 mEq/L, NKH 14.9 +/- 3.0 mEq/L), [TCO2 ] (DKA 23.5 +/- 5.0 mmol/L, NKH 24.1 +/- 4.2 mmol/L), arterial blood pH (DKA 7.42 +/- 0.09, NKH 7.51 +/- 0.14) and arterial blood PaCO2 (DKA 31.8 +/- 6.7 mm Hg, NKH 34.2 +/- 8.3 mm Hg) did not differ between the two groups. Linear regression of the decrease in serum [K] value during treatment, (Delta[K]), on the presenting serum [K] concentration,([K]2 ), was: DKA, Delta[K] = 2.78 - 0.81 x [K]2 , r = -0.85, p < 0.001; NKH, Delta[K] = 2.44 - 0.71 x [K]2 , r = -0.90, p < 0.001. The slopes of the regressions were not significantly different. Stepwise logistic regression including both DKA and NKH cases identified the presenting serum [K] level and the change in serum [TCO2 ] value during treatment as the predictors of Delta[K] (R2 = 0.81). Hyperkalemia is a feature of severe hyperglycemia (DKA or NKH) occurring in patients on dialysis. Insulin administration brings about correction of DKA and return of serum [K] concentration to the normal range in the majority of the hyperglycemic episodes without the need for other measures. The initial serum [K] value and the change in serum [TCO2 ] level during treatment influence the decrease in serum [K] value during treatment of dialysis-associated hyperglycemia with insulin.