Kinetic mode switch of rat brain IIA Na channels in Xenopus oocytes excised macropatches

Na currents recorded from inside-out macropatches excised from Xenopus oocytes expressing the subunit of the rat brain Na channel IIA show at least two distinguishable components in their inactivation time course, with time constants differing about tenfold ( _h1 = approx. 150 s and _h2 = approx. 2 ms). In excised patches, the inactivation properties of Na currents changed with time, favoring the faster inactivation kinetics. Analysis of the fast and slow current kinetics shows that only the relative magnitudes of _h1 and _h2 components are altered without significant changes in the time constants of activation or inactivation. In addition, voltage dependence of both activation and steady-state inactivation of Na currents are shifted to more negative potentials in patches with predominantly fast inactivation, although reversal potentials and valences remained unaltered. We conclude that the two inactivation modes discerned in this study are conferred by two states of Na channel the interconversion of which are regulated by an as yet unknown mechanism that seems to involve cytosolic factors.     

The mechanisms of fast renal compensation

Summary The changes in blood concentration which result in the adjustment of excretion when renal functioning mass is acutely reduced have been investigated by means of paired experiments on isolated dog kidneys. One kidney was perfused with undiluted blood; the other kidney was perfused with blood supplemented with an amount of water and solutes corresponding to the amount retained after the suppression of the contralateral kidney in situ; the response was evaluated from the difference in excretion between the two organs. The results may be summarized as follows: a) the adjustment of the excretion of water, sodium, potassium and urea results from small changes in blood concentration (haematocrit, plasma proteins and solutes), in the absence of specific stimuli of extrarenal origin; b) increased urea concentration is not the major determinant of the readjustment of sodium and water excretion; c) the response is potentiated by high arterial blood pressure; d) if the load of water exceeds the load of sodium, this ion is retained by the kidney even in the presence of an osmotic load of urea; e) the changes in the blood concentrations do not provide an adequate adjustment of the excretion of phosphate; f) increased excretion per nephron results from decreased fractional reabsorption without significant change in glomerular filtration rate.     

The effects of buffer ingestion on metabolic factors related to distance running performance

We examined the effects of sodium bicarbonate (BIC) and sodium citrate (CIT) ingestion on distance running performance. Seven male runners [mean = 61.7 (SEM 1.7) ml · kg^–1 · min^–1] performed three 30-min treadmill runs at the lactate threshold (LT) each followed by a run to exhaustion at 110% of LT. The runs were double-blind and randomly assigned from BIC (0.3 g · kg body mass^–1), CIT (0.5 g · kg body mass^–1) and placebo (PLC, wheat flour, 0.5 g · kg body mass^–1). Venous blood samples were collected at 5, 15 and 25 min during the run and immediately post-exhaustion (POST-EX) and analysed for pH, and the concentrations of lactate ([1a^–]_b) and bicarbonate ([HCO₃ ^– ]). Performance was measured as running time to exhaustion at 110% of LT (TIME-EX). The pH was significantly higher (P 0.05) for the BIC and CIT trials during exercise, but not POST-EX compared to PLC. The [1a^–]_b was significantly higher (P 0.05) for the CIT trial compared to PLC during exercise, and for both CIT and BIC compared to PLC at POST-EX. Blood [HCO₃ ^–] was significantly higher (P 0.05) during exercise for BIC compared to PLC. TIME-EX was not significantly different among treatments: BIC 287 (SEM 47.4) s; CIT 172.8 (SEM 29.7) s; and PLC 222.3 (SEM 39.7) s. Despite the fact that buffer ingestion produced favourable metabolic conditions during 30 min of high intensity steady-state exercise, a significant improvement in the subsequent maximal exercise run to exhaustion did not occur.     

Multiplicity of allergens in peanuts

Crude peanut protein fractions from raw and roasted peanuts were examined in the RAST with 10 sera from patients showing clinical peanut sensitivity. The radioactive uptake results, which were generally high, did not reveal any distinguishable pattern. Two commercially available peanut proteins, peanut lectin and phospholipase D, gave poor RAST responses. Three purified peanut proteins, α-arachin, conarachin I, and concanavalin A-reactive glycoprotein, all gave significant RAST results that were generally lower than those obtained with the crude extracts. The extent of RAST inhibition obtained with these materials was inversely related to their abundance in the total peanut protein. Crossed immunoelectrophoresis with extracts from raw and roasted peanut indicated the presence of 22 and 10 anodically migrating antigens, respectively. Sixteen IgE binding antigens were revealed for raw peanut and seven for roasted peanut after incubation with a mixed serum from the 10 patients in crossed radioimmunoelectrophoresis (CRIE) using ¹²⁵I-labeled anti-IgE. CRIE plates treated with individual serum samples showed that all the patients had specific IgE for the major antigen peak, which has been tentatively identified as α-arachin. This major storage protein of peanut, which is known to be particularly heat resistant, may be of greater clinical significance than its apparently low RAST activity would seem to indicate.     

Sodium regulation of agonist and antagonist binding to β-adrenoceptors in intact and Ns-deficient membranes

Summary Agonist binding to various hormone receptors mediating adenylate cyclase inhibition is decreased by sodium ions. We studied the influence of Na⁺ on agonist and antagonist binding to -adrenoceptors in membrane preparations of guinea pig lung, S49 lymphoma wild-type cells (WT) and their N_s-deficient cyc^– variants by measuring binding of the antagonist, [¹²⁵I]iodocyanopindolol ([¹²⁵I]CYP). At 37° C, sodium decreased the receptor affinity for the agonist, isoproterenol, in all three membrane preparations. In lung and WT membranes, Na⁺ steepened the shallow agonist competition curves in a manner similar to and synergistic with guanine nucleotides. When binding was performend at 4° C, sodium regulation but not guanine nucleotide regulation of agonist binding was preserved. At the low temperature, [¹²⁵I]CYP affinity was reduced, and sodium increased [¹²⁵I]CYP binding in both N_s-containing and N_s-deficient membranes by increasing the antagonist affinity without significant change in total receptor number. Compared to Na⁺, Li⁺ and K⁺ were much less potent and efficient in decreasing agonist and increasing antagonist binding. Na⁺ and Mg²⁺ had opposite effects on agonist binding in the N_s-containing lung and WT membranes but not in the N_s-deficient cyc^– membranes. The data indicate that sodium not only regulates binding of inhibitory hormone receptors but also agonist and antagonist binding to the adenylate cyclase stimulatory -adrenoceptor. The finding that sodium regulation of -adrenoceptor binding is also observed in the N_{s 2} cyc^– membranes, furthermore, indicates that the target of sodium is not the -subunit of N_s but possibly a component common to both types of receptor systems regulating adenylate cyclase activity.     

Effects of sodium and GTP on the binding kinetics of [3H]diprenorphine in NG 108-15 cell membranes

Summary Equilibrium binding isotherms of [³H]diprenorphine in membranes from NG 108-15 cells are consistent with a homogenous population of binding sites. Upon addition of Na⁺, Mg²⁺ and GTP, only a 2-fold reduction in affinity with a minor decrease in the number of sites is observed. Dissociation curves of [³H]diprenorphine, however, are clearly biphasic: in the absence of Na⁺, Mg²⁺ and GTP, 80% of the bound ligand dissociates slowly with at _1/2 of 100 min, and only 20% rapidly (t _1/2 4.5 min). In the presence of Mg²⁺, nearly all the binding is found in the slowly dissociating form. Upon the addition of either Na⁺ or GTP, 20–30% of the binding dissociates more rapidly. The rate constant of the rapidly dissociating form generated by Na⁺, however, is 2.5 times greater than that induced by the presence of GTP. Thus, the addition of both, Na⁺ and GTP, converts about 80% of the receptor into a very fast dissociating form (t _1/2 1.7 min).Exposure of intact cells to pertussis toxin (10 ng/ml) or treatment of membranes with N-ethyl maleimide (500 M), strongly reduces the proportion of the slowly dissociating component. Following these treatments, the effect of GTP is reduced or abolished, but that of Na⁺ remains unaffected.We conclude from these data that the effects of Na⁺ and GTP are not only distinct in site but also in mechanism of action and that there are three forms of opioid receptors that can be differentiated by their kinetic properties. The slowly dissociating receptor form requires a functional N unit.     

急诊经皮冠状动脉介入手术冠脉内应用硝普钠与替罗非班治疗老年急性心肌梗死效果及影响因素分析

目的探讨急诊经皮冠状动脉介入手术(Percutaneous Coronary Intervention,PCI)冠脉内应用硝普钠与替罗非班治疗老年急性心肌梗死效果及影响因素分析。方法收集153例急性心肌梗死老年患者,进行急诊PCI冠脉内应用硝普钠与替罗非班治疗(实验组)76例和急诊PCI冠脉内应用硝酸甘油与替罗非班治疗组(对照组)77例。追踪测评患者血清肌钙蛋白Ⅰ(Cardiac TroponinⅠ,cTnⅠ)、谷胱甘肽过氧化物酶(Glutathione,GSH)、超氧化物歧化酶(Superoxide Dismutase,SOD)、N末端B型钠尿肽前体(N-terminalpro-B-typenatriureticpeptide,NT-proBNP)、白介素-6(Interleukin-6,IL-6)、肿瘤坏死因子-α(Tumor Necrosis Factor-α,TNF-α)、内皮素(Endothelin,ET)、一氧化氮(NO)、血栓素B_2(Thromboxane B_2,TXB_2)、6酮-前列腺素F1α(6-keto-prostaglandin F1 alpha,6-keto-PGF1α)以及左心室射血分数(Left Ventricular Ejection Fraction,LVEF)、心肌梗死溶栓试验血流分级(Thrombolysis In Myocardial Infarction,TIMI分级)、心功能改善效果。结果实验组c TnⅠ、GSH、SOD、NT-pro BNP、IL-6、TNF-α、ET、NO、TXB_2、6-keto-PGF1α、LVEF、心功能改善效果、TIMI的追踪组间得分及复测组间得分差异有统计学意义(F=23.129、24.742、25.510、26.048、26.444、25.371、28.320、22.322、25.317、26.372、24.314、24.512、22.147,均P<0.05)。结论急诊PCI冠脉内应用硝普钠与替罗非班治疗老年急性心肌梗死患者对于心功能改善效果显著提高,并其受年龄、身体质量指数(Body Mass Index,BMI)、并发症、病变血管数量以及干预前心功能等级的影响。     

Effect of saline infusion on net reabsorption of endogenous sulfate relative to that of phosphate in intact and thyroparathyroidectomized rats

Clearance experiments have been performed to study the effects of saline infusion on the reabsorption of inorganic sulfate (SO₄) at endogenous levels. Adult female Sprague-Dawley rats on a standard diet were used. Both intact and thyroparathyroidectomized (TPTX) animals were infused with a 130 mmol/l sodium chloride solution at a low (0.15 ml/min) and a high (0.375 ml/min) rate. This increase of the infusion rate decreased the reabsorption of SO₄ in both groups of animals significantly. The fractional excretion of SO₄ in theintact rats increased from 9.9±5.6 to 18.4±3.6% (mean values±SD,p<0.001) and in theTPTX rats from 5.3±2.5 to 22.4±6.3% (p<0.001). It is concluded that endogenous parathyroid hormone has no major effect on the saline-induced inhibition of reabsorption of SO₄.This work was supported by a grant from the Deutsche Forschungsgemeinschaft (Fr 239/9-1)     

Altered gating and conductance of Na+ channels in hyperkalemic periodic paralysis

Electrophysiological studies on muscle fibres from patients with hyperkalemic periodic paralysis with myotonia have shown that the episodes of weakness are caused by a sustained depolarization of the sarcolemma to potentials between -40 and -60 mV. In muscle fibre segments from three such patients this sustained depolarization was caused by noninactivating Na⁺ channels with reduced single-channel conductance blocked by TTX and procainamide. As the chloride conductance was normal, myotonia may be best explained with the abnormal reopenings of the Na⁺ channels. The recently described genetic linkage between hyperkalemic periodic paralysis with myotonia and the gene coding for the TTX-sensitive Na⁺ channel suggests an altered primary structure of this channel causing its abnormal function.     

含有十二烷基磺酸钠的生物制剂的内毒素检测不能采用鲎试验

重组人ＩＬ－２在大肠杆菌表达时形成包含体，需经过变性和复性才具有生物学活性，在分离提取过程中常加一定量的ＳＤＳ，最低浓度每毫升不小于０．２５ｍｇ；低于此浓度会发生沉淀。鲎试验（ＬＡＬ试验）是一种灵敏度很高的检查生物制剂中致热源的常规方法。我们发现，当样本中ＳＤＳ的浓度＞０．０２５ｍｇ／ｍｌ时，可抑制尝试制的酶反应，使阳性结果转变为阴性。据此，我们建议，凡生物制剂中含有ＳＤＳ或其他酶抑制剂的产品，以尝试验来检查内毒素含量是没有意义的。