Focal cerebral ischaemia induces a decrease in activity and a shift in ouabain affinity of Na+, K+-ATPase isoforms without modifications in mRNA and protein expression

In a mouse model of focal cerebral ischaemia, we observed after 1 h of ischaemia, that the total Na+, K+-ATPase activity was decreased by 39.4%, and then did not vary significantly up to 6 h post-occlusion. In the sham group, the dose-response curves for ouabain disclosed three inhibitory sites of low (LA), high (HA) and very high (VHA) affinity. In ischaemic animals, we detected the presence of only two inhibitory sites for ouabain. After 1 h of permanent occlusion, the first site exhibited a low affinity while the second site presented an affinity intermediate between those of HA and VHA sites, which evolved after 3 h and 6 h of occlusion towards that of the VHA site. The presence of only two ouabain sites for Na+, K+-ATPase after ischaemia could result from a change in ouabain affinity of both HA and VHA sites (alpha2 and alpha3 isoforms, respectively) to form a unique component. Irrespective of the duration of ischaemia, the smaller activity of this second site accounted entirely for the loss in total activity. Surprisingly, no modifications in protein and mRNA expression of any alpha or beta isoforms of the enzyme were observed, thus suggesting that ischaemia could induce intrinsic modifications of the Na+, K+-ATPase.     

Release of serotonin in the locus coeruleus of normotensive and spontaneously hypertensive rats (SHR)

The aim of the present work was to clarify whether differences exist between the release of endogenous serotonin in the locus coeruleus of normotensive and hypertensive rats. The locus coeruleus was superfused with artificial cerebrospinal fluid (aCSF) through a push-pull cannula and serotonin and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) were determined in the superfusate by HPLC combined with electrochemical detection. Compared with normotensive Wistar-Kyoto (WKY) rats, the basal release rate of serotonin in the locus coeruleus of spontaneously hypertensive rats (SHR) was increased more than twofold. Intravenous infusion of noradrenaline (4 μg/kg min) increased mean arterial blood pressure to the same extent in hypertensive and normotensive rats. The pressor response was associated with an increased serotonin release. In WKY rats, the release of serotonin in the locus coeruleus evoked by noradrenaline infusion was more pronounced than in SHR. In WKY rats, intravenous infusion of sodium nitroprusside (150 μg/kg min) led to a fall in blood pressure which was less pronounced and lasted shorter than in SHR. The depressor response was associated with decreased serotonin release. In WKY rats, the decrease in serotonin release evoked by sodium nitroprusside was more pronounced and lasted longer than in SHR. Neither noradrenaline nor sodium nitroprusside influenced the outflow of 5-HIAA. The sensory stimuli noise and tail pinch led to a slight rise in arterial blood pressure which was similar in WKY rats and SHR. These stimuli enhanced the release rate of serotonin and the outflow of 5-HIAA to the same extent in the locus coeruleus of normotensive and hypertensive rats. The findings suggest that the enhanced release of serotonin in the locus coeruleus of genetically hypertensive rats reflects a mechanism counteracting the disturbed blood pressure homeostasis. Stressors influence blood pressure and release of serotonin in the locus coeruleus of SHR and WKY rats to the same extent. Received: 16 November 1998 / Accepted: 22 February 1999     

Dose-dependent alteration of rat cardiac sodium current by isoproterenol: Results from direct measurements on multicellular preparations

Conflicting results have been reported in literature about the influence of-adrenergic stimulation on the fast cardiac sodium current (I _Na ⁺). To elucidate these mechanisms in multicellular preparations we used the loose-patch-clamp technique to evaluate the effect of the-adrenergic agonist isoproterenol 1–1000 nmol/l. Isoproterenol enhancedI _Na+ at all membrane potentials by elevation of the maximal availableI _Na ⁺. Only at the high concentration of 1 mol/l wasI _Na ⁺ slightly depressed after depolarizing conditioning clamps. The most marked increase of the maximal availableI _Na ⁺ was 30 ± 9 % after application of 100 nmol/l isoproterenol. To learn about the mechanisms in view of sodium channel modulation we combined isoproterenol with the sodium channel blocker lidocaine (47 mol/l). Under these circumstances the effects of both drugs were completely independent. This investigation shows clearly that low concentrations of isoproterenol increaseI _Na+ in multicellular preparations by a gating-independent mechanism.     

The influence of external sodium and potassium on lithium uptake by primary brain cell cultures at ‘therapeutic’ lithium concentration

The ionic regulating of lithium homeostasis and steady-state intra: extracellular lithium distribution in the brain can be approached by experimental methods using intact nerve cells in vitro. Primary cultures prepared from chick embryonic brain were applied to study the effect of extracellular sodium and potassium on the lithium uptake of nerve cells at therapeutic lithium concentration (1.5 mM). Lithium influx and the level of steady-state intracellular lithium were significantly reduced by increasing the external sodium concentration. At physiological extracellular sodium level, the steady-state content of lithium in the brain cells was about half of that observed in the presence of 10 mM sodium in the incubation media and the value of the intra: extracellular lithium distribution ratio was below 1. External potassium (0.5–3 mM) strongly inhibited lithium uptake of the nerve cells. Ouabain (10^-4 M) had no effect on this potassiumsensitive lithium uptake in Tyrode media. Sodium influx studied by isotope tracer methodology was higher in cultures preloaded with lithium as compared to that of the controls. It can be concluded that sodium and potassium ions, at physiological concentrations, significantly influence lithium uptake as well as the intra: extracellular lithium distribution in brain cell cultures.     

Comparison of the urinary excretion of arsenic metabolites after a single oral dose of sodium arsenite,monomethylarsonate, or dimethylarsinate in man

Summary The urinary elimination of the metabolites of arsenic has been followed up as a function of time in volunteers who ingested a single oral dose of arsenic (500 g As) either as sodium arsenite (As_i), monomethylarsonate (MMA), or cacodylate (DMA). The excretion rate increased in the order As_i < DMA < MMA. After 4 days, the amount of arsenic excreted in urine represents 46, 78, and 75% of the ingested dose in the case of As_i, MMA and DMA, respectively. With regard to the in vivo biotransformations, it is concluded that DMA is excreted unchanged; MMA is slightly (13%) methylated into DMA while roughly 75% of the arsenic excreted after ingestion of As_i is methylated arsenic (about 1/3 as MMA and about 2/3 as DMA).This study was supported by a grant from the Commission of the European Communities     

Aprindine blocks the sodium current in guinea-pig ventricular myocytes

Summary Aprindine is a class Ib antiarrhythmic agent. We studied effects of aprindine (3 µmol/l) on the Na⁺ current using whole cell voltage clamp (tip resistance = 0.5 , [Na]_i and_o = 10 mmol/l at 18°C). Aprindine revealed tonic block (Kd_rest = 37.7 µmol/l, Kd_i = 0.74 µmol/l; n = 4). Aprindine, shifted inactivation curve to hyperpolarizing direction by 11.4 ± 3.5 mV (n = 4) without changes in slope factor. In the presence of 3 µmol/l aprindine, aprindine showed phasic block, i.e., duration-dependent block at 2 Hz (64% ±3070 at 1.5 ms, 82%±6% at 20 ms, 93%±7% at 200 ms; n = 4). Short single prepulse also produced aprindine-induced phasic block (12% at 1.5 ms, 22% at 100 ms; n = 2). After removal of fast inactivation of Na⁺ current by 3 mmol/l tosylchloramide sodium, aprindine revealed phasic block, independent of holding potential. The recovery time constant from aprindine-induced phasic block was 4.8 s at holding potential = –100 mV and 5.0 s at holding potential = –140 mV. This use-dependent block of aprindine had pH dependency. Under acidic condition (pH 6.0), 3 µmol/l aprindine showed smaller use-dependent block (14% ± 7% at 2 Hz; n = 4) comparing with either at pH 7,4 (68% ± 13%; n = 4) or at pH 8.0 (90% ±12%; n = 4).The results suggest that aprindine could bind to the receptor via activation process through channel pore, resulting in decrease of Na⁺ current, and egress from the receptor through the lipid bilayer. These effects might be attenuated under acidic condition due to changes in intracellular ratio of charged to neutralized form of drug molecule. Send offprint requests to: R. Sato at the above address     

Effects of sodium and temperature on tension in isolated canine coronary artery

The effects of sodium and temperature on tension of isolated canine coronary arterial strips were studied.In 20mEq·l ^–1 K solution, the strength of tension was inversely related to the Na concentration. At 37°C, the tension was significantly increased at 70mEq·l ^–1 Na and below. The tension was gradually suppressed by lowering of the temperature from 37°C to 10°C. At 10°C, tension did not developed significantly at Na concentrations between 127mEq·l ^–1 and 12mEq·l ^–1.It was concluded that the decrease in Na concentrations increased the tension of the canine coronary artery and the lowering of temperature supressed the tension inducted by the decrease in Na concentrations.(Yoshida K, Fujii Y, Ina H, et al.: Effects of sodium and temperature on tension in isolated canine coronary artery. J Anesth 5: 56–59, 1991)     

Comparative cardiovascular effects of SNP,ATP and phentolamine during norepinephrine-induced hypertension in dogs

There has been no study comparing the advantage and disadvantage of various antihypertensive agents during surgery for pheochromocytomas because the study is difficult in clinical setting. In the present experiments using dogs, after increasing the arterial blood pressure with norepinephrine, we decreased it to the baseline with sodium nitroprusside (SNP), adenosine triphosphate (ATP), or phentolamine (PE) and compared the hemodynamic changes. A hyperdynamic state was found with ATP and with PE, but not with SNP. The norepinephrine-induced pulmonary hypertension could be successfully treated with SNP, but not with ATP or PE. The reason for these differences are thought to be the different vasodilative properties on peripheral arteries and veins. We conclude that agents that dilates the arteries and veins should be used to regulate the arterial pressure during surgical removal of a pheochromocytoma.(Murata K, Takahashi H, Ikeda K: Comparative cardiovascular effects of SNP, ATP and phentolamine during norepinephrine-induced hypertension in dogs. J Anesth 5: 396–403, 1991)     

Administration of obidoxime tablets to man

Twenty-four male volunteers were given obidoxime tablets in quantities ranging from 1.84–3.58 g in a single dose, or 7.36 g divided into 4 equal doses. With the lowest dose, average peak plasma level of the drug was 1.9 g/ml and after the highest single dose it was 5.6 g/ml, both attained 1.5 h after administration. In the multiple-dosed individuals, plasma levels of the oxime increased gradually following each additional dose, reaching a peak of 3.5 g/ml after the last dose.Thirteen individuals complained of one or more of the following side effects: pallor, nausea, pyrosis, headache, generalized weakness, sore throat, and paresthesia of the face muscles.Activities of blood cholinesterase, glutamic oxalacetic transaminase, glutamic pyruvic transaminase, as well as hematocrit values, heart rate, and blood pressure were not affected.It is postulated that due to the undesirable side effects, the general use of obidoxime tablets should not be recommended. However, prophylactic oral treatment with obidoxime could be considered for persons at high risk of organophosphate poisoning or when parenteral administration might not be feasible.     

丙戊酸钠缓释片的制备及其释放度的测定

目的 研制丙戊酸钠缓释片并进行体外释放度测定。方法 采用喷雾干燥法制备丙戊酸钠微囊，通过电镜和X-射线衍射等检测方法对微囊进行质量评价。采用永停滴定法测定丙戊酸钠微囊含量及缓释片的体外释放度。结果 喷雾干燥法制备的丙戊酸钠微囊质量较好，所制缓释片体外释放符合一级动力学过程。结论 运用丙戊酸钠微囊制备缓释片的工艺简便、可靠，体外释放证明有明显的缓释作用。