右旋美托咪定后处理对大鼠心肌缺血再灌注损伤的保护作用

目的：评价右旋美托咪定（DEX）后处理对大鼠心肌缺血再灌注时Na⁺-K⁺-ATP酶和Ca²⁺-ATP酶活性的影响。方法：36个成年雄性Wistar大鼠心脏置于改良的Langendoff装置上,均为平衡灌注末HR>180次/min、左室收缩压>75mm Hg、室性早搏<2个/min的心脏模型,采用随机数字表法分为3组：对照组（A组）、缺血再灌注组（B组）、DEX处理组（C组）,每组12个。A组持续灌注KH液180 min,B组和C组在KH平衡灌注20 min时常温停灌40 min后恢复灌注,于再灌注即刻分别灌注KH液、含100 nmol·L^-1 DEX的KH液20 min,然后继续再灌注KH液100 min。监测心率（HR）、冠状动脉流出量（CF）,左心室发展压（LVDP）、左心室内压最大上升和下降速率（±dP/dt_max）,采用酶联免疫法测定心肌Na⁺-K⁺-ATP酶、Ca²⁺-ATP酶,以梗死心肌质量占心室质量的百分比表示心肌梗死率。结果：再灌注后A组心功能优于B组、C组（P<0.05）,C组优于B组（P<0.05）。与A组比较,B组和C组心肌梗死率较大,心肌组织Na⁺-K⁺-ATP酶、Ca²⁺-ATP酶的活性降低（P<0.05）;与B组比较,C组心肌梗死率低,心肌组织Na⁺-K⁺-ATP酶、Ca²⁺-ATP酶的活性较高（P<0.05）。结论：DEX后处理可提高Na⁺-K⁺-ATP酶和Ca²⁺-ATP酶的活性,减轻大鼠心肌缺血再灌注损伤。     

Inhibition of P-type ATPases by [(dihydroindenyl)oxy]acetic acid (DIOA), a K+ -Cl- cotransporter inhibitor

[(Dihydroindenyl)oxy]acetic acid (DIOA) has been used as a potent inhibitor of K⁺–Cl⁻ cotransporter (IC₅₀ = 10 μM). Here we found that DIOA inhibited activities of P-type ATPases such as dog kidney Na⁺,K⁺-ATPase (IC₅₀ = 53 μM), hog gastric H⁺,K⁺-ATPase (IC₅₀ = 97 μM) and rabbit muscle Ca²⁺-ATPase (IC₅₀ = 127 μM). In the membrane preparation of the LLC-PK1 cells stably expressing rabbit gastric H⁺,K⁺-ATPase, DIOA inhibited activities of the endogenous Na⁺,K⁺-ATPase (IC₅₀ = 95 μM) and the exogenous H⁺,K⁺-ATPase (IC₅₀ = 75 μM). 5-Nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB), a Cl⁻ channel blocker, had no effects on the DIOA-elicited inhibition of the P-type ATPases. These findings suggest that lower concentration of DIOA (< 20–30 μM) should be used for evaluation of the activity of K⁺–Cl⁻ cotransporter without affecting the activities of coexisting Na⁺,K⁺-ATPase and/or H⁺,K⁺-ATPase in cells.     

苦参碱对阿霉素所致H9c2心肌细胞损伤的保护作用及与线粒体Na+-K+-ATP酶、Ca2+-ATP酶关系的研究

目的：研究苦参碱对阿霉素所致H9c2心肌细胞损伤的保护作用及其机制。方法：将H9c2心肌细胞培养,取2~3代细胞进行试验,共分为4组。对照组：接受生理盐水作为干预因素;阿霉素组：接受0.5 mg·L^-1阿霉素作为损伤模型;苦参碱+阿霉素组：接受0.5 mg·L^-1阿霉素和不同浓度苦参碱（50,150,200 mg·L^-1）作为干预因素;苦参碱组：接受不同浓度苦参碱（50,150,200 mg·L^-1）作为干预因素。以上各组相应干预24 h后,应用流式细胞仪检测H9c2心肌细胞凋亡水平,应用分光光度法检测线粒体Na⁺-K⁺-ATP酶、Ca²⁺-ATP酶活性,利用JC-1法检测线粒体膜电位。结果：与阿霉素组相比,苦参碱+阿霉素组H9c2心肌细胞凋亡显著减少、线粒体Na⁺-K⁺-ATP酶、Ca²⁺-ATP酶活性显著升高（P<0.05）、线粒体膜电位显著改善。结论：苦参碱对阿霉素所致H9c2心肌细胞有保护作用,减轻心肌细胞凋亡,改善线粒体膜电位、提高线粒体Na⁺-K⁺-ATP酶、Ca²⁺-ATP酶活性。     

玉郎伞水提物对心肌缺血再灌注损伤心肌组织ATP酶和凋亡蛋白的影响

目的:研究玉郎伞水提物(WYLS)对大鼠离体心脏缺血再灌注(I/R)损伤心肌组织Na⁺-K⁺-ATP酶、Ca²⁺-ATP酶和凋亡蛋白的影响。方法:采用Langendorff离体心脏灌流法,停灌30 min再灌30 min建立大鼠心肌缺血再灌注损伤模型。观察WYLS对心肌组织Na⁺-K⁺-ATP酶、Ca²⁺-ATP酶活性的影响、心肌组织病理学变化、凋亡相关蛋白Bcl-2和Bax表达的影响。结果:与I/R组比较,WYLS高剂量组Na⁺-K⁺-ATP酶、Ca²⁺-ATP酶的活性明显增加(P<0.05或P<0.01),心肌受损程度明显减轻(P<0.05)。同时,WYLS高剂量组心肌Bax蛋白表达明显降低(P<0.01),Bcl-2蛋白表达无明显影响(P>0.05),但Bcl-2/Bax的比率明显增加(P<0.05)。结论:WYLS能减轻大鼠心肌I/R损伤,作用机制可能与减轻钙超载、抑制某些凋亡相关蛋白表达有关。     

白藜芦醇对心肌缺血再灌注过程中线粒体的保护

目的:探讨白藜芦醇对心肌缺血再灌注损伤过程中Ca²⁺-ATPase及HSP70表达的影响。方法:健康雄性SD大鼠40只,采用随机数字量表法分为4组(假手术组、缺血再灌注组、缺血预适应组、白藜芦醇组),采用结扎冠状动脉前降支制备心肌缺血再灌注损伤模型,于结扎前15 min及再灌注前1 min经舌下静脉注射白藜芦醇10 mg·kg^-1。提取心肌线粒体,紫外可见光分光光度计测定线粒体中SDH、Na⁺-K⁺-ATPase、Ca²⁺-ATPase活性;荧光分光光度计测定线粒体中游离钙、mPTP开放度及跨膜电位;RT-PCR及Western blot检测心肌组织HSP70、Ca²⁺-ATPase mRNA及蛋白质的表达。结果:白藜芦醇与缺血再灌注组及缺血预适应组相比,线粒体中SDH、Na⁺-K⁺-ATPase、Ca²⁺-ATPase的活性明显提高(P<0.05或P<0.01);线粒体内钙离子浓度明显下降(P<0.05或P<0.01)、mPTP开放程度减小(P<0.01)、线粒体膜电位增高(P<0.01);Ca²⁺-ATPase、HSP70在 mRNA或蛋白水平上的表达均有所增加(P<0.05或P<0.01)。结论:白藜芦醇可能通过增加心肌组织中Ca²⁺-ATPase、HSP70 mRNA和蛋白的表达,提高线粒体Ca²⁺-ATPase的活性,产生对大鼠心肌缺血再灌注损伤时线粒体的保护作用。     

Inhibiting effect of cytotoxic bromine-containing compounds from sponges (Aplysinidae) on Na-K-ATPase activity

—The bromine-containing compounds from sponges of the Aplysinidae family inhibit, in vitro, the Na⁺-K⁺-ATPase activity of the rat brain microsomal fraction. The extent of inhibition is dependent on concentration and chemical structure of the compounds. The substances containing the dienone fragment, such as 3,5-dibromo-1-hydroxy-4-oxo-2,5-cyclohexadien-1-acetamide (IV), 3,5-dibromo-1-acetoxy-4-oxo-2,5-cyclohexadien-1-acetonitrile (V) and 3,5-dibromo-1-hydroxy-4-oxo-2,5-cyclohexadien-1-ethylacetate (VI), are powerful inhibitors of Na⁺-K⁺-ATPase.     

The toxicity of H2O2 on the ionic homeostasis of airway epithelial cells in vitro.

Oxygen species may be formed in the air spaces of the respiratory tract in response to environmental pollution such as particulate matter. The mechanisms and target molecules of these oxidants are still mainly unknown but may involve modifications of the ionic homeostasis in epithelial cells. Cytosolic concentrations of Ca²⁺ (Fura2) and Na⁺ (SBFI) and short-circuit current (Isc) were followed in primary cultures of human nasal epithelial cells and in the cell line 16HBE14o⁻ after exposure to H₂O₂ or ·OH (H₂O₂+Fe²⁺). Cells were grown on glass coverslips for ionic imaging or on permeable snapwell inserts for Isc studies. Exposure of the apical as well as the basal side of the cultures to H₂O₂ or ·OH induced a concentration-dependent transient increase in Isc which is due to a transient secretion of Cl⁻. Ca_i also increased transiently with approximately the same kinetics. The response was dependent on the release of calcium from intracellular stores. Na_i on the contrary increased steadily over more than an hour. When the apical membrane was permeabilized with gramicidin, ·OH inhibited the Na⁺ current (a measure of Na⁺-K⁺-ATPase activity in the baso-lateral membrane). The arrest of the pump was significant after 30 min exposure to oxidant. On the other hand no increase in the apical or baso-lateral sodium conductances could be detected. The progressive arrest of the Na⁺/K⁺-pump may contribute to the sustained elevation of Na_i. This strong modification in the cellular ionic homeostasis may participate in the stress response of the respiratory epithelium through alterations in signal transduction pathways.     

Binding domain of oligomycin on Na(+),K(+)-ATPase

Oligomycin inhibits Na⁺,K⁺-ATPase activity by stabilizing the Na⁺ occlusion but not the K⁺ occlusion. To locate the binding domain of oligomycin on Na⁺,K⁺-ATPase, the tryptic-digestion profile of Na⁺,K⁺-ATPase was compared with the profile of Na⁺ occlusion within the digested Na⁺,K⁺-ATPase in the presence of oligomycin. The Na⁺ occlusion profile is responsible for the digestion profile of the -subunit, which is the catalytic subunit of the ATPase. The effect of oligomycin on chimeric Ca²⁺-ATPase activity was examined. The chimera used, in which the 163 N-terminal amino acids of chicken sarcoplasmic/endoplasmic reticulum Ca²⁺-ATPase 1 were replaced with the 200 N-terminal amino acids of the chicken Na⁺,K⁺-ATPase 1-subunit, partially retains the Na⁺-dependent characteristics of Na⁺,K⁺-ATPase, because the chimeric Ca²⁺-ATPase activity is activated by Na⁺ but inhibited by ouabain, a specific inhibitor of Na⁺,K⁺-ATPase (Ishii, T., Lemas, M.V., Takeyasu, K., 1994, Proc. Natl. Acad. Sci. U. S. A., 91, 6103–6107). Oligomycin depressed the activation by Na⁺ of the chimeric Ca²⁺-ATPase activity. These findings suggest that the 200 N-terminal amino acids of the Na⁺,K⁺-ATPase -subunit include a binding domain for oligomycin.     

The effect of the myotoxic Lys49 phospholipase A2 from Agkistrodon contortrix laticinctus snake venom on Na/K-ATPase activity of toad bladders

ACLMT is a myotoxic Lys49 phospholipase A₂ isolated from the venom of the snakeAgkistrodon contortrix laticinctus. We have previously shown that ACLMT increases baseline water transport and partially inhibits vasopressin-stimulated water transport across toad bladders due to an increase in cytosolic calcium. However, these evidences provide insufficient insight into the mechanisms involved in the effects of ACLMT on membrane permeability. In an attempt to better understand such mechanisms, the current study aimed to investigate whether the Na⁺/K⁺-ATPase activity of isolated toad bladders can be affected by the ACLMT and the synthetic peptide from its C-terminal region. The toxin significantly decreased the Na⁺/K⁺-ATPase, while the peptide did not alter it. These findings suggest that the effects of ACLMT on membrane permeability may be due to the inhibition of the Na⁺/K⁺-ATPase activity, and that the C-terminal region may not play a relevant role in this effect. This study contributes toward a better understanding of the mechanisms involved in the toxicity of the snake venom Lys49 PLA₂ myotoxins on biological tissues.     

人参皂苷三醇型与二醇型在不同量比下对大鼠机体燥性的影响研究

目的 探究人参皂苷三醇型与人参皂苷二醇型含量比值变化对大鼠机体的燥性影响.方法 将30只SD大鼠随机分为空白组和4个实验组(R值=0.5、1、1.5、2),每组6只.采用Elisa法测定大鼠血中Na+-K+-ATP酶、Ca2+-Mg2+-ATP酶、乳酸脱氢酶(LDH)、琥珀酸脱氢酶(SDH)以及脑中胆碱酯酶(ChE)、...     

黄芪多糖对脓毒症急性肾损伤大鼠AMPK/SIRT1信号通路介导的肾上皮细胞能量代谢的影响

目的：研究黄芪多糖（APS）对脓毒症急性肾损伤（AKI）大鼠肾上皮细胞能量代谢的影响。方法： 60只大鼠随机抽取10只设为正常组,其余随机分为AKI组,APS低、高剂量组各10只,地塞米松组11只。建模后6,12,18 h时APS低、高剂量组APS 100,200 mg·kg^-1灌胃,地塞米松组地塞米松10 mg·kg^-1灌胃,正常组及AKI组等量生理盐水灌胃。建模后24 h测磷法检测肾上皮细胞钠-钾-三磷酸腺苷酶（Na^＋-K^＋-ATP）活性;Western blot法检测肾组织沉默信息调节因子2相关酶类1（SIRT1）。结果：与AKI组比较,APS低、高剂量组,地塞米松组Na^＋-K^＋-ATP酶活性增强（t=3.894,P=0.005;t=6.564,P<0.01;t=6.565,P<0.01）;与APS低剂量组比较,APS高剂量组、地塞米松组Na^＋-K^＋-ATP酶活性增强（t=2.544,P=0.034;t=2.635,P=0.030）;与AKI组比较,APS低、高剂量组,地塞米松组SIRT1蛋白表达量升高（t=9.923,P<0.01;t=12.042,P<0.01;t=10.960,P<0.01）;与APS低剂量组比较,APS高剂量组、地塞米松组SIRT1蛋白表达量升高（t=4.985,P=0.001;t=5.000,P=0.001）。结论： APS可改善脓毒症AKI大鼠肾上皮细胞能量代谢,可能与激活AMPK/SIRT1信号通路有关。     

Sanguinarine: A positive inotropic alkaloid which inhibits cardiac Na,K-ATPase

In isolated, isometrically contracting left guinea pig atria, sanguinarine, a benzophenanthridine alkaloid from the papaveracea Sanguinaria canadensis, produced a concentration-dependent positive inotropic effect. Between 2.3 × 10⁻⁶ M and 6.5 × 10⁻⁵ M, sanguinarine increased contractility by 108% which was comparable to the maximal inotropic effect of ouabain. Within the same concentration range, sanguinarine caused inhibition of Na⁺,K⁺-ATPase isolated from guinea pig myocardium. 100% inhibition of Na⁺,K⁺-ATPase activity occurred at 1 × 10⁻⁴ M sanguinarine. The I₅₀ for enzyme inhibition and the ED₅₀ for the inotropic action of sanguinarine were the same (6–6.5 × 10⁻⁶ M) indicating that both effects may be causally related.     

Relationship of anesthetic activity of alkyl acetates to hydrophobicity and in vivo effect on membrane fluidity in mice

In vivo anesthetic activity of alkyl acetates in mice was studied in relation to hydrophobicity and the in vivo effect on membrane fluidity. The anesthetic potency (AD₅₀) of alkyl acetates was determined; AD₅₀ shows the i.p. dose required to anesthetize 50% of mice from the treated group. We used log P (n-octanol/water partition coefficient) as an operational definition of hydrophobicity. Membrane fluidity was determined using 1,6-diphenyl-1,3,5-hexatriene (DPH) as fluorescence probe. Log (1/AD₅₀) was a parabolic function of log P, and the value of log P that corresponds to the minimum AD₅₀ was estimated to be 2.08. Brain synaptosomal membranes were prepared from mice 30 min after dosing with each of the three alkyl acetates applied at 1.5-fold AD₅₀: n-butyl, n-amyl, and n-hexyl acetate. In each alkyl acetate group, most of the animals were anesthetized (>68%). Decreased membrane fluidity was observed for the animals that were anesthetized while no change in the fluidity was seen for the animals that were not anesthetized. The results suggest an involvement of decreased DPH fluidity in alkyl acetate-induced anesthesia. Received: 24 March 1997 / Accepted: 27 May 1997     

大黄配伍药对的泻下作用变化及其共性关系研究

目的：研究大黄配伍药后对其泻下作用的变化及其共性关系。方法：将140只实验动物随机分为生理盐水组、果导组及大黄药对组（15 g·kg^-1、7.5 g·kg^-1,以大黄生药计）,按10 mL·kg^-1的剂量给药后,分别用代谢笼积分法、酚红糊排空法、炭末推进作用及Na⁺-K⁺-ATPase活性实验,比较大黄配伍药对对大鼠的正常泻下作用、酚红糊肠推进功能、炭末推进率及Na⁺-K⁺-ATPase活性。结果：大黄与药对配伍后泻下作用均有不同程度的改变,与生理盐水组比较,大黄、大黄牡丹及大黄桃仁15 g·kg^-1剂量组显著增加正常小鼠泻下作用、促进肠推进功能、提高炭末推进率及抑制Na⁺-K⁺-ATPase活性,表明其泻下作用有显著差异;且与大黄组比较,大黄桃仁及大黄牡丹配伍后的泻下作用有差异,其中泻下作用最显著的是大黄牡丹组。结论：大黄与牡丹、桃仁、甘遂配伍可促进其泻下作用,与枳实、黄连配伍则可抑制其泻下作用,这可能与配伍中药的主要化学成分引起大黄中蒽醌类化合物的溶出量变化及药对间的相使相须作用有关。     

Similarities of the in vivo and in vitro effects of mercuric chloride on H]ouabain binding and potassium activation of Na/K-ATPase in isolated rat cerebral microvessels

A previous study revealed that a single i.p. administration of 6 mg/kg body wt. of mercuric chloride (MC) durably inhibits the rat cerebral microvascular Na⁺/K⁺-ATPase activity [1]. In this study, cerebral microvessels isolated 18 h after MC treatment were compared to those obtained from control rats and subsequently treated or not treated with MC in vitro, with regard to: (a) ³H]ouabain binding to, and (b) K⁺-activation kinetics of, the Na⁺/K⁺-ATPase. Microvessels from MC-treated rats showed a decrease of ³H]ouabain binding down to 62% of the control binding, and the same degree of inhibition was attained in microvessels treated in vitro with 5 μM MC. Analysis of the K⁺-activation kinetics of Na⁺/K⁺-ATPase revealed a decrease of V_max from the control value of 13.1 to 7.67 μmol/mg/h in microvessels from MC-treated rats and 6.07 μmol/mg/h in microvessels treated in vitro with 5 μM MC, with no change in K_m in either case. The similarity of the effects of in vivo and in vitro treatments suggests that the inhibition of the cerebromicrovascular Na⁺/K⁺ATPase following in vivo administration of MC results from a direct interaction of Hg⁺ with the enzyme.     

Sodium-pump injury and arrhythmogenic transient depolarizations in catecholamine-induced cardiac hypertrophy

The pathogenesis of arrhythmogenic transient depolarizations (TDs) was studied by means of electrophysiological and cytochemical methods in normal and hypertrophied left ventricular myocardium of the rat. In hypertrophy induced by administration of 5 mg/kg isoprenaline once daily for 7 days, the myocardial membrane was depolarized, the action potential duration was prolonged and the _max was decreased, as compared with those of age-matched normal controls. TDs induced by a train of action potentials could be observed in hypertrophied myocardium, but not in normal control myocardium. Ryanodine completely abolished TDs, but the β-adrenoceptor agonist noradrenaline and the adenylate cyclase activator forskolin were without effect. In cytochemical studies, the Na⁺,K⁺-ATPase activity was localized in the sarcolemma, and three times as much reaction product, which appeared on the inner side of the cell membrane, was found in the normal myocardium than in the hypertrophied myocardium. The results suggest that catecholamine-induced cardiac hypertrophy damages the membrane-bound Na⁺,K⁺-ATPase and causes a cAMP-independent intracellular Ca overload and TDs, thereby permitting abnormal impulse formation, which predisposes the diseased myocardium to develop arrhythmias.     

Prednisolone-3,20-bisguanylhydrazone: The mode of interaction with rat brain sosium and potassium-activated adenosine triphosphatase

The mechanism of interaction between prednisolone-3,20-bisguanylhydrazone (PBGH) and Na⁺,K⁺-ATPase (ATP phosphohydrolase, EC 3.6.1.3) was studied using partially purified rat brain enzyme preparations. PBGH inhibited Na⁺,K⁺-ATPase rapidly and reversibly. The enzyme-inhibiting action of PBGH was competitively antagonized by potassium. PBGH inhibited Na⁺, Mg²⁺ and ATP-supported binding of (³H)-ouabain to the enzyme. When PBGH was added to the incubation mixture at the time when the (³H)-ouabain binding was close to its equilibrium state, the concentration of (³H)-ouabain enzyme complex was rapidly reduced and shifted to a lower equilibrium state. A double reciprocal plot analysis of the (³H)-ouabain binding data indicates that the inhibition of ouabain binding by PBGH is apparently competitive. Binding of (³H)-ouabain in the presence of Tris-phosphate and Mg²⁺ was also inhibited by unlabeled PBGH. Thus, it appears that the binding of PBGH precludes the bindings of ouabain to Na⁺,K⁺-ATPase.     

Effects of Fe on ion channels: Na channel, delayed rectified and transient outward K channels

The effects of Fe²⁺ on the properties of three types of ion channels were studied in acutely dissociated rat hippocampal pyramidal neurons from area CA1 at postnatal ages of 7–14 days using the whole cell patch clamp technique. The results indicated that: (1) in the existence of Fe²⁺, the activation voltage threshold of transient outward K⁺ currents (I_A) was decreased. The normalized current-voltage curves of activation were well fitted with a single Boltzmann function, and the V_1/2 was 2.44±1.14 mV (n=15) in control, whereas 1.79±1.53 (n=15), −2.96±0.92 (n=14), −5.11±1.31 (n=13), −9.05±1.64 mV (n=12) in 1, 10, 100 and 1000 μ Fe²⁺, respectively. Differences between two groups were significant (P<0.05, n=12–15), except for that between the control and 1 μ (P>0.05, n=15). (2) Fe²⁺ caused a left shift of the current–voltage curves of steady-state inactivation of I_A in a concentration-dependent manner. The curves were well fitted with a single Boltzmann function with similar slope (P>0.05, n=10–13). The V_1/2 were −70.71±1.23 (n=13), −71.14±1.37 (n=13), −78.21±1.17 (n=11), −84.61±1.34 (n=12), and −89.68±2.59 mV (n=10) in control, 1, 10, 100 and 1000 μ Fe²⁺, respectively. Fe²⁺ also shifted the current–voltage curves of Na⁺ channel steady-state inactivation to more negative depolarization potentials in parallel, with V_1/2, −67.37±1.33 mV (n=12) in control, and −67.52±1.28 mV (n=12), −68.24±1.61 mV (n=10), −71.58±1.45 mV (n=10), −76.65±1.76 mV (n=9) in 1, 10, 100 and 1000 μ Fe²⁺ solutions, respectively. (3) In Fe²⁺ solutions, the recovery from inactivation of I_A was slowed. (4) With application of different concentrations of Fe²⁺, the voltage threshold of activation of delayed rectified outward K⁺ currents (I_K) was decreased, while Fe²⁺ showed a little inhibition at more positive depolarization. Briefly, the results demonstrated that Fe²⁺ is a dose- and voltage-dependent, reversible modulator of I_A, I_K and Na⁺ channels. The results will be helpful to explain the mechanism of Fe²⁺ physiological function and Fe²⁺ intoxication in the central nervous system.     

Na,K-ATPase activity is selectively increased in thalamus in thiamine deficiency prior to the appearance of neurological symptoms

The relationship between progression of neurological status and the activities of both Na⁺,K⁺- and Mg²⁺-dependent-ATPase (adenosine 5′-triphosphate phosphohydrolase) was investigated in brain regions of pyrithiamine-induced thiamine deficient rats. Thalamic Na⁺,K⁺-ATPase activity was selectively increased by 200% (P < 0.01) prior to the appearance of symptoms of thiamine deficiency and normalized in symptomatic rats. This selective transitory activation precludes a mediation by brain soluble fraction Na⁺,K⁺-ATPase modifiers as does the unaltered distribution in regional high-affinity [³H]ouabain binding densities observed throughout the time-course used in these experiments. Na⁺,K⁺-ATPase maintains cellular ionic gradients and has been implicated in neurotransmitter uptake and release mechanisms. The fact that the increased thalamic Na⁺,K⁺-ATPase activity coincides with the early alterations in serotonin metabolism observed in similarly treated animals and the concomitantly early increase in glucose utilization previously observed in the thalamus of thiamine-deficient rats is discussed.     

Conformational analysis: a tool for the elucidation of the antioxidant properties of ferulic acid derivatives in membrane models

With the aim to search and design more effective and safe antioxidant molecules to be used as functional ingredients in cosmetic formulations for UV protection, we evaluated the antioxidant/radical scavenging activities of ferulic acid and of some alkyl ferulates in both acellular and cellular systems. Ferulic acid esters, equipotent as antioxidant in homogeneous phase, showed when tested in membranous systems (rat liver microsomes, rat erythrocytes) marked differences in antioxidant potency. The n-C₁₂ derivative was the most potent, followed by n-C₈, n-C₁₆ and branched C₈, and then by ferulic acid.

A conformational study carried out by NMR and modelling, indicates that the different antioxidant activity of ferulates in membrane models is due to the different spatial conformation and arrangement of the side chain of the molecule, which governs the access and binding to the phospholipid bilayer, the modality of orientation of the scavenging/quenching nucleus (phenol moiety), and hence the overall antioxidant potency of the derivative.

These results emphasize the need of analytical studies (NMR and molecular modelling) addressed to the knowledge of the conformational parameters in combination with conventional antioxidant testings for understanding the antioxidant behaviour of a molecule in a biological membrane/system.