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 30s、1min和 2min后 ,海马神经细胞外Na 活度分别低于对照组 2 7 7mmol/L、5 0 3mmol/L和 5 7 8mmol/L ,而K 活度则分别高于对照组 2 3mmol/L、2 4mmol/L和 2 9mmol/L(P <0 0 1)。 3min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 0 1)。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。     

蝙蝠葛碱减轻家兔快速心房起搏间隙连接蛋白40降解

目的：观察家兔快速心房起搏所致的心房肌间隙连接蛋白40（connexin 40, Cx40）的改变及蝙蝠葛碱（DAU）的防治效果。方法：40只家兔随机分为3组：对照组（n=8）、DAU组（n=8）、起搏组（n=12）、起搏+DAU组（n=12）。经颈内静脉将电极置入右心房，后两组以600 beat/min行快速心房起搏，同时DAU组和起搏+DAU组于快速起搏前30 min按5 mg·kg^-1静脉给予DAU，另两组给等容量的生理盐水。连续刺激8 h后开胸取右心耳组织，分别用生化方法检测心房肌Na⁺、K⁺和Ca²⁺含量，用Western blot检测心房肌Cx40含量，并用透射电镜观察超微结构。结果：起搏组心房肌Na⁺、Ca²⁺含量高于对照组和DAU组，而Cx40及K⁺含量低于对照组和DAU组（P<0.01），心房肌细胞超微结构损伤明显。起搏+DAU组心肌Na⁺、Ca²⁺含量低于起搏组（P<0.05，P<0.01），而Cx40和K⁺含量高于起搏组（P<0.05，P<0.01），Cx40的降解和心房肌细胞超微结构损伤轻于起搏组。结论：钙超载可能参与持续快速心房起搏引起的Cx40降解。DAU能明显减轻快速心房起搏引起的Cx40的降解，对快速起搏导致的心肌细胞损伤有拮抗作用。     

PTSD样情感行为异常大鼠海马ATP酶活性与Ca2+/CaM改变

目的:探讨创伤后应激障碍(PTSD)精神与行为异常的病理生理基础。方法:通过频率25Hz、波宽1ms、串长10s、串隔7min、强度100μA的恒流、单向方波, 建立海马惊厥阈下电刺激PTSD动物模型;采用神经生化、流式细胞仪、荧光标记术及Westernblotting等方法, 定量观测了实验动物海马Na⁺-K⁺-ATP酶、Ca²⁺-ATP酶活性, 细胞内Ca²⁺含量与钙调素(CaM)相对活性平均通道荧光及海马组织总CaM表达的动态变化规律。结果:电刺激停止后48h内实验动物海马细胞线粒体Na⁺-K⁺-ATP酶活性明显下降, 72h内Ca²⁺-ATP酶活性显著降低;海马细胞[Ca²⁺]i于电刺激停止后72h内明显增高, 游离CaM平均通道荧光则同步降低, 而海马组织总CaM表达则于电刺激停止后48h内明显增多。结论:海马细胞[Ca²⁺]i持续增高、结合CaM含量明显增加及线粒体钠钾泵与钙泵功能受损, 可能是实验动物长时程PTSD样情感行为异常的重要病理生理基础之一。     

米诺环素抑制MPP+诱导的PC12细胞凋亡和线粒体功能损伤

目的: 探讨米诺环素(minocycline)对1-甲基-4-苯基吡啶离子(MPP⁺)诱导的PC12细胞凋亡和线粒体功能损伤的保护作用。方法: 将MPP⁺加入体外培养的的 PC12 细胞中, 建立多巴胺能神经元凋亡模型, 实验过程中用minocycline进行预处理,四甲基偶氮唑盐法(MTT法)检测细胞存活率,Hoechst染色检测细胞凋亡,DCFH-DA检测ROS聚集,JC-1检测细胞线粒体膜电位变化。结果: 0.5 mmol/L MPP⁺处理PC12细胞24 h,能明显抑制细胞生长(抑制率80.8%),诱导细胞发生凋亡(凋亡率5.22%),同时ROS浓度提高230.0%,线粒体膜去极化(绿/红荧光强度比为11.95)。而加入10 μmol/L minocycline预处理30 min可明显升高MPP⁺处理的 PC12 细胞活性,细胞凋亡率明显降低(P<0.01),ROS浓度明显下降,绿/红荧光强度比也明显降低(P<0.01)。结论: Minocycline抑制MPP⁺诱导的PC12细胞凋亡部分通过对抗其线粒体功能而发挥作用。     

K+通道在正常与慢性低氧大鼠低氧性肺血管收缩反应中的作用

目的:探讨K⁺通道在慢性低氧致低氧性肺血管收缩反应降低中的作用。方法:采用离体肺灌流实验,研究4-AP(4-aminopyridine,电压依赖性K⁺通道-Kv阻滞剂)、TEA(tetraethylamonium,Ca²⁺激活性K⁺通道-K_Ca阻滞剂)、GLIB(glibenclamide,ATP敏感性K⁺通道-K_ATP阻滞剂)对正常与慢性低氧大鼠肺血管低氧反应的影响。结果:4-AP、TEA均可使正常大鼠肺动脉基础压上升,且使其肺血管低氧反应明显增强;对于慢性低氧大鼠,其肺血管对低氧反应明显低下,4-AP、TEA升肺动脉基础压的作用明显低于对照鼠肺,GLIB也呈现升高肺动脉基础压力作用,4-AP、TEA、GLIB均可使肺血管低氧反应大大增强,增强的比例明显大于正常对照组。结论:在离体灌流鼠肺HPV中,Kv、K_Ca的开放起调节作用,大鼠经慢性低氧后,肺血管反应性明显降低,可能与Kv、K_Ca、K_ATP在HPV中的调节作用相对增强有关。     

镁对哮喘患者外周血CD4+ CD25+调节性T细胞凋亡及Foxp3表达的影响

目的:观察镁对分离培养的健康人和哮喘患者外周血CD4⁺CD25⁺调节性T细胞凋亡及叉头框蛋白3(Foxp3)表达的影响。方法:经磁珠分离法分离出健康人和哮喘患者外周血CD4⁺CD25⁺T细胞,分镁剂干预组(10 mmol/L)及空白组培养72 h后,用流式细胞仪检测CD4⁺CD25⁺T细胞的凋亡率及Foxp3表达情况。结果:(1)健康人外周血CD4⁺CD25⁺T细胞的纯度为77.4％~92.3%,哮喘患者CD4⁺CD25⁺T细胞的纯度为75.2％~93.8％。(2)CD4⁺CD25⁺T细胞占外周血CD4⁺T细胞的比例在健康组为4.12%~7.98%,在哮喘组为4.51%~8.68%,两者没有显著差异(P＞0.05)。(3)镁(10mmol/L)可以诱导健康组及哮喘组外周血CD4⁺CD25⁺T细胞凋亡率增加(P＜0.05),但对Foxp3的表达无影响(P＞0.05)。结论:镁促进CD4⁺CD25⁺T调节细胞凋亡增加可能为其治疗支气管哮喘的作用机制之一。     

缺血预处理快速效应对兔急性缺血脊髓的保护作用

目的:探讨缺血预处理快速相对兔腹主动脉短暂阻断致缺血脊髓的保护作用。方法:36只雄性新西兰兔随机分成3组(n=12):即缺血再灌注损伤组(IR组)、缺血预处理组(IPC+IR组)及假手术组(Sham组)。IR组阻闭兔腹主动脉肾下段20min,复制兔脊髓缺血损伤模型;IPC+IR组预先阻闭腹主动脉肾下段6min,再灌注30min后再次阻闭腹主动脉肾下段20min;Sham组除不夹闭腹主动脉外,其余处理同IR组。再灌注后8h、12h、24h和48h分别对动物神经功能评分,然后,处死动物取脊髓(L_5-7),分别行组织病理学观察及测定脊髓组织中Na⁺,K⁺-ATP酶的活性。结果:Sham组及IPC+IR组神经功能评分各时点均明显高于IR组(P＜0.01);Sham组及IPC+IR组脊髓前角正常神经细胞数明显多于IR组(P＜0.01);Sham组及IPC+IR组脊髓组织中Na⁺,K⁺-ATP酶的活性明显高于IR组(P＜0.01)。结论:缺血预处理快速相对兔急性缺血脊髓有显著的保护作用,这种保护作用可能与稳定Na⁺,K⁺-ATP酶的活性有关。     

NO在外源性高浓度Ca2+损伤心肌线粒体中的作用

目的：探讨一氧化氮在外源性高浓度Ca²⁺损伤心肌线粒体中的作用。方法：正常心肌线粒体分为单纯L-精氨酸（L-Arg）组、Ca²⁺损伤组和左旋硝基精氨酸甲酯（L-NAME）保护组,分别于含有20 μmol/L EDTA、100 μmol/L CaCl₂以及1 μmol/L L-NAME+100 μmol/L CaCl₂的反应介质中孵育,然后测定线粒体活力、膜电位以及NO含量。结果：Ca²⁺损伤组线粒体活力、膜电位明显下降,而NO^-₂/NO^-₃含量升高,且线粒体活力、膜电位与NO₂^-/NO₃^-含量呈显著负相关（r=-0.5297,P<0.01;r=-0.6041,P<0.01）;L-NAME保护组线粒体活力与膜电位均明显高于Ca²⁺损伤组,但仍低于L-Arg组,而NO₂^-/NO₃^-含量低于Ca²⁺损伤组,且与L-Arg组无明显差异。结论：外源性Ca²⁺可激活线粒体一氧化氮合酶,使NO生成增多,后者在线粒体活力与膜电位降低中起重要作用。     

支气管哮喘病人CD4+T细胞CD25、CD30表达状况

目的：通过观察哮喘病人外周血CD4⁺T细胞CD25、CD30表达水平，了解哮喘病人T细胞活化状态。方法：将分离出的CD4⁺T细胞分别用PPD、PHA刺激，最后用流式细胞仪检测抗原刺激前后细胞表面CD25、CD30表达水平。结果：①哮喘病人CD4⁺T细胞CD25、CD30自然表达比率均低于健康对照（P<0.05、P<0.05）。②用PHA刺激哮喘病人CD4⁺T细胞后，CD25表达水平明显高于健康对照（P<0.01），但CD30表达无差异。③PPD刺激组CD25、CD30表达与健康对照间无差异。结论：哮喘病人CD4⁺T细胞活化状态明显异常。哮喘病人的CD4⁺T细胞无刺激因素时，活化水平低下，但接受刺激后表现出高水平的活化状态。     

β-淀粉样蛋白对D-半乳糖致衰大鼠海马线粒体膜流动性的影响

目的:研究β-淀粉样蛋白(β-AP)对衰老大鼠海马线粒体膜流动性的影响。方法:用D-半乳糖(D-gal)建立衰老动物模型,并且海马内微注射β-AP;检测各组大鼠学习记忆行为;以DPH为荧光探针,测定大鼠海马线粒体膜粘滞系数,同时测定海马Na⁺-K⁺ATP酶活性的变化。结果:D+A组大鼠Na⁺-K⁺ATP酶活性明显低于D组和A组(P＜0.05),与N组比较有显著差异(P＜0.01);海马线粒体膜流动性显著低于N组(P＜0.01),与D组和A组比较也有显著差异(P＜0.05)。结论:β-AP与D-gal联合可导致脑海马自由基损伤效应加重,海马线粒体膜流动性显著降低,Na⁺-K⁺ATP酶活性明显降低。     

Potassium and sodium shifts during in vitro isometric muscle contraction,and the time course of the ion-gradient recovery

Intracellular potassium ([K⁺]_i), interstitial potassium ([K⁺]_inter), intracellular sodium ([Na⁺]_i), and resting membrane potential (RMP) were measured before and after repetitive stimulation of mouse soleus and EDL (extensor digitorum longus) muscles. At rest, RMP was –69.8 mV for soleus and –74.9 mV for EDL (37°C). [K⁺]_i was 168 mM and 182 mM, respectively. In soleus, free [Na⁺]_i was 12.7 mM. After repetitive stimulation (960 stimuli) RMP had decreased by 11.9 mV for soleus and by 18.2 mV for EDL. [K⁺]_i was reduced by 32 mM and 48 mM, respectively, whereas [K⁺]_inter was doubled. In soleus [Na⁺]_i had increased by 10.6 mM, demonstrating that the [K⁺]_i-decrease is three times higher than the [Na⁺]_i-increase. It is concluded that this difference reflects different activity induced movements of Na and K, and that the difference is not due to the Na/K pumping ratio. The possible involvement of the potassium loss in muscle fatigue is discussed. After stimulation RMP recovered with a time constant of 0.9 min for soleus and 1.5 min for EDL. Within the first minutes after stimulation the intracellular potassium concentration increased by 20.4 mM/min for soleus and 21.7 mM/min for EDL. Free [Na⁺]_i decreased with less than 10 mM/min. The mechanisms underlying the different rate of changes are discussed.Parts of this work have been published in preliminary form (Juel and Sjøgaard 1984)     

Extracellular ionic variations during spreading depression

Changes in the concentrations of K⁺, Ca²⁺, Na⁺ and Cl^? were measured during spreading depression in the exposed lissencephalic cerebellar molecular layer of the catfish,Corydoras aneus. Liquid ion exchanger ion-selective microelectrodes were used in pairs to monitor simultaneously changes in the concentrations of two ionic species in the extracellular space. Normothermic spreading depression in the catfish cerebellum consists of a slow negative potential shift that develops at a rate of 2–3mV/s, reaches an amplitude of ?25 mV, lasts 1–6 min and propagates at a rate of 0.5–1.5 mm/min. [K⁺]_o rises from a resting level of 2.3–35 mM at the peak of spreading depression. Between 20 and 40s later [Ca²⁺]_o falls from 2.2 mM to 0.8 mM and [Na⁺]_o and [Cl^?]_o decrease from 149 to 57 mM and 137 to 47 mM respectively at approximately the same time. [Ca²⁺]_o, [Na⁺]_o and [Cl^?]_o decreases begin when [K⁺]_o exceeds 10 mM.These results establish the magnitude and temporal sequence of the major ion concentration changes in extracellular space during spreading depression. The earliest extracellular precursor of spreading depression is a rise in [K⁺]_o. In light of the equality of [Na⁺]_o and [Cl^?]_o changes and the rise in [K⁺]_o, electroneutrality in extracellular space involved may be maintained by the net accumulation of some unidentified anion equivalent to the rise in [K⁺]_o. Alternatively, no net accumulation is needed if some extracellular anions are impermeant and the volume of extracellular space decreases. The sum of the extracellular ion concentrations suggests that the ionic strength of extracellular space decreases by greater than one-third during spreading depression. These results demonstrate that the brain is capable of establishing and recovering from local ionic inhomogenejties.     

Changes in extracellular potassium and calcium in rat cerebellar cortex related to local inhibition of the sodium pump

Extracellular K⁺, Ca²⁺, and Na⁺ ([K⁺]_e, [Ca²⁺]_e, [Na⁺]_e) were recorded with ion selective microelectrodes in the cerebellar cortex of urethane-anesthetized rats. Superfusion of the cerebellum with artificial cerebrospinal fluid containing K-strophanthidin (10^–6–10^–4 mol/l) or other cardioactive steroids, known to be inhibitors of the sodium/potassium pump, had the following effects: elevation of resting [K⁺]₃, reduction of poststimulus K⁺-undershoots, decrease of resting [Ca²⁺]_e and [Na⁺]_e. For instance, at 3×10^–5 mol/l K-strophanthidin within the superfusion solution (the unknown intracerebellar concentration being certainly much smaller), [K⁺]_e was elevated up to 130% and [Ca²⁺]_e reduced to 70% of their resting values. Iontophoretic K⁺-pulses were enhanced in amplitude at the same time. Control experiments with iontophoretic TMA application demonstrated that the glycoside effects were not due (or in higher concentrations only partly due) to shrinkage of the extracellular fluid volume. When tetrodotoxin (10^–7 mol/l) or Mn²⁺ (1–3 mmol/l) were additionally superfused, K-strophanthidin effects were qualitatively similar, though quantitatively smaller. This indicates that part of the effects were indirect via neuronal activity evoked by the blockade of the sodium pump. The experiments show that reduction of sodium pump activity in cerebellar cortex has rapid and serious consequences on the distribution of potassium and calcium in the extracellular space, resulting in an alteration of neuronal circuit excitability.     

Sodium dependence of the epithelial sodium conductance expressed in Xenopus laevis oocytes

The epithelial Na⁺ conductance was expressed in Xenopus laevis oocytes by injection of size-fractionated mRNA of bovine tracheal epithelium. Fractionation was achieved by sucrose density gradient centrifugation. Successful expression was analysed by recording current/voltage (I/V) curves in the presence and absence of amiloride (10 mol/l). The newly expressed conductance was half-maximally inhibited by 44 nmol/l amiloride and exhibited a selectivity for Na⁺ over K⁺ of 1401. I/V curves obtained at different extracellular Na⁺ concentrations ([Na⁺]_o) were subjected to a Goldman-fit analysis to obtain the relation between Na⁺ permeability (P _Na) and [Na⁺]_o. The data show that decreasing [Na⁺]_o from 85 mmol/l to 0.85 mmol/l increased P _Na by more than threefold, which is thought to reflect Na⁺ channel inhibition by increasing [Na⁺]_o. This effect clearly exceeded what can be attributed to concentration saturation of single Na⁺ channel conductance (Palmer and Frindt (1986) Proc Natl Acad Sci USA 83:2767). No correlation of inhibition with intracellular Na⁺ concentration was observed. Preservation of the [Na⁺]_o-dependent self-inhibition by the newly expressed Na⁺ conductance suggests that it is an intrinsic property of the Na⁺ channel protein, probably mediated by an extracellular Na⁺ binding site.     

Na+ dependence of single-channel current and channel density generate saturation of Na+ uptake in A6 cells

 In high-resistance, salt-absorbing epithelia the apical amiloride-sensitive Na⁺ channel is the key site for regulation of salt and water balance. The saturation of macroscopic Na⁺ transport through these channels was investigated using A6 epithelial monolayers. The relation between transepithelial Na⁺ transport (I _Na) and apical Na⁺ concentration ([Na⁺]_ap) under short-circuit conditions was studied. Michaelis-Menten analysis of the saturable short-circuit current (I _sc) yielded an apparent Michaelis-Menten constant (K _m ^I ) of 5 mmol/l and a maximal current (I _max) of 8 μA/cm². The microscopic parameters underlying I _Na, namely the single-channel current (i) and the open channel density (N _o), were investigated by the analysis of current fluctuations induced by the electroneutral amiloride analogue CDPC (6-chloro-3,5-diaminopyrazine-2-carboxamide). A two-state model analysis yielded the absolute values of i (0.18 ± 0.01 pA) and N _o (65.38 ± 9.57 million channels/cm² of epithelium) at [Na⁺]_ap = 110 mmol/l containing 50 μmol/l CDPC. Our data indicate that in A6 cells both i and N _o depend on [Na⁺]_ap. Between 3 and ≈ 20 mmol/l the density of conducting pores, N _o, decreases sharply and behaves again as an almost [Na⁺]_ap-independent parameter at higher [Na⁺]_ap. The single-channel current clearly saturates with an apparent Michaelis-Menten constant, K _m ⁱ , of ≈ 17 mmol/l. Thus, the [Na⁺]_ap dependence of N _o as well as the limited transport capacity of the amiloride-sensitive Na⁺ channel are both responsible for the saturation of I _Na. Received: 2 June 1997 / Received after revision: 12 November 1997 / Accepted: 10 December 1997     

Effects of reduced electrochemical Na+ gradient on contractility in skeletal muscle: role of the Na+-K+ pump

 Continued excitation of skeletal muscle may induce a combination of a low extracellular Na⁺ concentration ([Na⁺]_o) and a high extracellular K⁺ concentration ([K⁺]_o) in the T-tubular lumen, which may contribute to fatigue. Here, we examine the role of the Na⁺-K⁺ pump in the maintenance of contractility in isolated rat soleus muscles when the Na⁺, K⁺ gradients have been altered. When [Na⁺]_o is lowered to 25 mM by substituting Na⁺ with choline, tetanic force is decreased to 30% of the control level after 60 min. Subsequent stimulation of the Na⁺-K⁺ pump with insulin or catecholamines induces a decrease in [Na⁺]_i and hyperpolarization. This is associated with a force recovery to 80–90% of the control level which can be abolished by ouabain. This force recovery depends on hyperpolarization and is correlated to the decrease in [Na⁺]_i (r = 0.93; P<0.001). The inhibitory effect of a low [Na⁺]_o on force development is considerably potentiated by increasing [K⁺]_o. Again, stimulation of the Na⁺-K⁺ pump leads to rapid force recovery. The Na⁺-K⁺ pump has a large potential for rapid compensation of the excitation-induced rundown of Na⁺, K⁺ gradients and contributes, via its electrogenic effect, to the membrane potential. We conclude that these actions of the Na⁺-K⁺ pump are essential for the maintenance of excitability and contractile force. Received: 19 December 1996 / Received after revision: 25 March 1997 / Accepted: 2 April 1997     

Effects of changes in extracellular potassium,magnesium and calcium concentration on synaptic transmission in area CA1 and the dentate gyrus of rat hippocampal slices

The dependence of stimulus-induced synaptic potentials on changes of extracellular ionic concentrations of potassium ([K⁺]_o 3, 5, 8 mM), magnesium ([Mg²⁺]_o 2, 4, 8 mM) and calcium [Ca²⁺]_o (2 mM and continuous lowering by washing with Ca²⁺-free solutions) was investigated in area CA1 and dentate gyrus of rat hippocampal slices. Field potentials (fps), [K⁺]_o and [Ca²⁺]_o were measured with double-barreled ion selective/reference microelectrodes. Paired pulse stimulation (interval 50-ms) was applied either to the lateral perforant path or to the Schaffer collaterals. Elevation of [K⁺]_o from 5 to 8 mM and of [Mg²⁺]_o from 2 to 8 mM depressed the rise of excitatory postsynaptic potentials, as well as the amplitude of population spikes. With elevation of [K⁺]_o, the effect was stronger in the dentate gyrus, while with elevation of [Mg²⁺]_o, the reduction was more pronounced in area CA1. During washout of Ca²⁺, synaptic potentials became reduced and finally depressed. The [Ca²⁺]_o at which synaptic transmission was blocked increased with higher [Mg²⁺]_o and decreased with a change of [K⁺]_o from 3 to 5 mM, whereas with an elevation of [K⁺]_o from 5 to 8 mM, it rose in area CA1 but was reduced in dentate gyrus. All ionic changes also affected frequency habituation and potentiation in paired pulse experimentes. In dentate gyrus, frequency habituation was reversed to frequency potentiation with moderate lowering of [Ca²⁺]_o and with elevation of [Mg²⁺]_o and [K⁺]_o. In contrast, in area CA1 frequency potentiation was reduced upon elevation of [K⁺]_o.     

Relationship between cell volume and cation content in thick ascending limb of rat kidney

We examined the relationship between the cell volume and cation concentration ([Na_i] and [K_i]) of isolated segments of rat medullary thick ascending limb (MAL) after incubation at 30°C in various isotonic solutions. When the tubules were incubated in a normal NaCl solution containing 5 mmol/l K⁺, addition of 1 mmol/l of ouabain increased [Na_i] and decreased [K_i] but did not change the total ([Na_i]+[K_i]) concentration (about 90 mEq/l) or tubular volume. After incubation in various K⁺-free solutions, the tubules were almost fully K⁺-depleted; their volume per unit of length was similar in the three solutions, although the choline Cl-treated tubules had a very low sodium content compared to the NaCl-and Na₂SO₄-treated tubules (8 vs. 97 and 95 mEq/l respectively). Ouabain altered neither volume nor [Na_i] of tubules incubated in choline Cl or Na₂SO₄ solution. Transfer of tubules from K⁺-free Na₂SO₄ or K⁺-free choline Cl solution into K⁺-free NaCl solution resulted in an increase in [Na_i] (by 29 and 97 mEq/l respectively) without much increase in tubular volume. A marked swelling of the tubules was only observed when the K⁺-free NaCl solution contained also ouabain. Under this condition, [Na_i] was comparable to the Na⁺ concentration of the incubation medium. After washing and incubation in a normal NaCl solution containing K⁺, the swollen tubules recovered their initial volume and restored Na⁺ and K⁺ concentration gradients across the cell membranes. The ([Na_i]+[K_i]) concentration centration measured in the tubules preincubated in choline Cl solution was always smaller than that of the tubules preincubated either in NaCl or Na₂SO₄ solutions, an observation suggesting that choline ions enter rat MAL cells. Barium (3 mmol/l) prevented tubular swelling. This inhibition corresponded to a smaller increase in [Na_i] than that observed in control tubules. Furosemide or bumetanide (even at 0.1 mmol/l) did not alter the increases in tubular volume and in Na⁺ content induced by ouabain. The data provide additional evidence that the isoosmotic swelling of MAL cells requires an almost full inhibition of Na⁺-pump activity and involves coupled net fluxes of Na⁺ and Cl^– ions.     

Potassium-induced relaxation in isolated cerebral arteries contracted with prostaglandin F2α

Summary In helically cut strips of canine cerebral arteries exposed to 5.4 mM [K⁺]_o and contracted with prostaglandin F₂, the addition of K⁺ in concentrations ranging from 0.5–5 mM caused a dose-related relaxation. The relaxing effect of K⁺ was potentiated at reduced [K⁺]_o and suppressed at reduced [Na⁺]_o. Reduction of Cl^– from bathing media failed to alter the effect of K⁺. Removal of external Ca²⁺ markedly attenuated the K⁺-induced relaxation and increase in [Ca²⁺]_o also attenuated the relaxation. Similar relaxation was induced by K⁺ in cerebral arteries from other species including humans, puppies, cats and rabbits. The addition of K⁺ also elicited a relaxation in peripheral arteries, including coronary, femoral, mesenteric and renal, contracted with prostaglandin, but this relaxation was markedly less than in cerebral arteries. The content of Na⁺ in freshly excised cerebral arteries was significantly greater than that of peripheral arteries, while the content of K⁺ in these arteries was not significantly different.The present study provides further evidence to support the hypothesis that an electrogenic Na⁺ pump is involved in the genesis of K⁺-induced relaxation. The Na⁺ pump does not appear to be fully activated at normal [K⁺]_o of 5.4 mM in cerebral arteries.