Effect of increased distal sodium delivery on organic osmolytes and cell electrolytes in the renal outer medulla

Sodium absorption in distal tubule segments was stimulated by increasing the distal delivery via infusion of hypertonic saline. In these animals, and in control rats, electrolyte concentrations in thick ascending limb cells, light and dark cells of the collecting duct in the outer and inner stripe of the outer medulla and in cells of the proximal straight tubule (outer stripe only) were studied. The measurements were performed by electron microprobe analysis of freeze-dried cryosections of the outer medulla. In addition, organic osmolytes (glycerophosphorylcholine, betaine and myo-inositol) were measured by high performance liquid chromatography in cortex and outer medulla. Augmented delivery of sodium chloride to the distal tubule was associated with increased sodium concentrations of thick ascending limb cells both in the outer and inner stripe and of medullary collecting duct light and dark cells in the outer stripe. While the sum of organic osmolyte concentrations was 28% higher in the outer medulla of the salt-loaded animals compared with controls, this value was unchanged in the renal cortex. These findings indicate that the primary event underlying stimulation of sodium absorption along the thick ascending limb during increased distal sodium delivery is enhanced entry of sodium across the apical cell membrane. This would be expected to lead to higher cell sodium concentrations and stimulation of basolateral active Na-K-exchange. The enhanced transport activity of outer medullary tubules may be associated with increased interstitial tonicities and intracellular retention of organic osmolytes.     

Hyperpolarizing current of the Na/K ATPase contributes to the membrane polarization of the Purkinje cell in rat cerebellum

 The contribution of the Na/K ATPase (pump) current to the polarization of the Purkinje cell has been studied using slices of the rat cerebellum by blocking the pump with dihydro-ouabain (DHO) while recording the membrane potential with microelectrodes in the somata. From our recordings, it appeared that blocking the pump depolarized the Purkinje cells more rapidly than might be expected from shifts in Na⁺ and K⁺ concentrations, suggesting the removal of a hyperpolarizing current. Application of DHO, in the presence of tetrodotoxin (TTX), led to calcium spike firing and plateau-like discharges suggesting activation of voltage-dependent calcium channels in the dendrites. Adding 2 mM Co²⁺ to the medium did not prevent the depolarizations. Removing calcium from the bathing medium containing 2 mM Co²⁺ blocked the spiking activity but DHO application still produced a depolarization. Experiments to measure the current inhibited by DHO indicated that the Na/K pump supplies a constant current of 240 pA. Substitution of the sodium with choline produced a hyperpolarization, during which DHO had no effect on the membrane potential. Substitution of the sodium with lithium produced only a slowly developing depolarization. It is concluded that in the cerebellar Purkinje cell, a continuous sodium ion influx activates the pumps which produce a current that directly contributes to the membrane polarization. Possible pathways for this sodium influx are discussed. Received: 3 April 1997 / Received after revision and accepted: 12 May 1997     

Potassium induced potential changes in rat diaphragm muscle

Summary The effect of different potassium concentrations on the membrane potential and membrane resistance of rat diaphragm muscle fibres was measured by means of a double sucrose gap method and a microelectrode technique. Concentration measurements showed that the muscle fibres gained sodium and lost potassium in the equilibration period.In the absence of external chloride changing the external potassium concentration from 2.8 mM to potassium-free caused a depolarization of the membrane of about 30 mV and a small increase in membrane resistance.This K-dependent potential change (K-response) was reduced by ouabain, K-strophanthin, 2,4-dinitrophenol and cyanide, indicating that an energy requiring process is involved. The temperature dependence of the K-response found is consistent with this assumption. Variation in potassium permeability in the absence and presence of external potassium could account for only 13% of the K-response.The K-response amplitude appeared to depend on the external potassium and the internal sodium concentration. Hyperpolarization of the membrane could not only be produced after readmission of potassium but also after addition of thallium, the latter being more potent. Raising the external chloride concentration resulted in a decrease of the K-response and membrane resistance. The current, generating the Kresponse was shown to be hardly influenced by conditional polarization of the membrane.It is concluded from these results that the Kresponse is mainly due to the operation of an electrogenic sodium pump.     

The effects of sodium butyrate,an inhibitor of histone deacetylase,on the cocaine- and sucrose-maintained self-administration in rats

In order to substantiate the concept that cocaine behavioral effects may be influenced by histone modification, rats were trained to self-administer cocaine intravenously (0.75 mg/(kg injection)), and were systemically pretreated with sodium butyrate (NaBu), a potent histone deacetylase inhibitor, before the test session during the maintenance phase. The effect of NaBu on a control reinforcer (sucrose)-induced self-administration was also assessed. NaBu (100–200 mg/kg) was inactive in altering the cocaine (0.75 mg/(kg injection))-maintained responding and at the highest dose (400 mg/kg) it did increase cocaine-induced lever presses during the maintenance phase. On the other hand, sucrose-reinforcing potential was not altered when NaBu was given at the highest dose (400 mg/kg). These findings extend previous observations that changes in histone acetylation are relevant to cocaine-induced behavioral effects. Given that histone acetylase inhibitor enhances cocaine-induced behavioral plasticity, the therapeutic benefits of histone acetyltransferase inhibitors warrant further investigation in the experimental models of cocaine abuse.     

Effect of hypothermia on renal sodium reabsorption

Summary The relationship between sodium reabsorption and oxygen consumption was studied in an isolated rabbit kidney preparation perfused with blood at 37, 28 and 19° C. When the temperature was lowered from 37° C to 28° C and to 19°C the rate of oxygen consumption and of the maximal P.A.H. excretion (Tm P.A.H.) decreased more than that of sodium reabsorption.TheQ ₁₀ for sodium reabsorption is about 1.8, while that for maximal P.A.H. excretion is 2.5. Some hypothesis on the possible mechanisms of the lowQ ₁₀ of the Na⁺ reabsorption are forwarded.Preliminary reports have been published [Boll. Soc. Ital. Biol. Sper.43, 1019–1023 (1966) and44, 1784–1787 (1967);45, 860–862 (1969) and45, 863–865 (1969)].     

Active Ca2+ reabsorption in the proximal tubule of the rat kidney

Summary Using the stop flow microperfusion technique with simultaneous capillary perfusion the rate of active Ca²⁺ reabsorption was evaluated by measuring the static head electrochemical potential difference as well as the permeability of the tubular wall for Ca²⁺ ions. Under control conditions the active Ca²⁺ transport was calculated to be 3.35×10^–13 mol/cm·s. It declined toward zero if the ambient Na⁺ was replaced by choline or lithium. Parallel experiments in the golden hamster showed that active Ca²⁺ transport, vanished completely if active Na⁺ transport was blocked by ouabain (1 mM). These data indicate that the active Ca²⁺ reabsorption from the proximal tubule depends on the active reabsorption of Na²⁺ presumably via a Na⁺–Ca²⁺ countertransport at the contraluminal cell membrane. The static head electrochemical potential difference of Ca²⁺ is the same in late and early proximal tubules. It is also not affected by the presence of acetazolamide (10^–4 M) by the absence of bicarbonate or glycodiazine buffer or by the absence or presence of phosphate (2 mM).     

Isolation and immunochemical characterization of the major allergen of birch pollen (Betula verrucosa)

The classification of some of the extractable birch pollen antigens as allergens was established by crossed radioimmunoelectrophoresis (CRIE). In CRIE the major allergen (antigen 23) exhibited the strongest “radiostaining” and only a few other components of birch pollen extract were visibly radiostained. The major allergen and a preparation containing mainly the minor allergens, antigens 25 and 19, were isolated from a crude aqueous birch pollen extract by a combination of anion-exchange, size-exclusion, and chelate chromatography. Antigen 23 was purified to near homogeneity. The molecular weights and the pIs of antigens 23, 25, and 19 were determined to be 17,000 daltons, pI 5.25 (5.5, 5.0); 25,000 daltons, pI 5.0 (4.9, 5.4); and 29,000 daltons, pI 6.2 (5.4), respectively. The classification of antigen 23 as the major allergen in birch pollen was supported by results of RAST inhibition experiments, RAST screening, and skin prick testing.     

The mechanisms of sodium current inhibition by benzocaine in the squid giant axon

(1) The effects of benzocaine on the ionic currents in the voltage-clamped squid giant axon have been examined under various conditions; intact axons internally perfused with CsF and axons dialysed with tetraethyl-ammonium ions were used. (2) Both the steady state outward (potassium) current and the early transient (sodium) current were reduced by ca. 50% by benzocaine (1 mM). (3) Plots of the changes produced by benzocaine (1 mM) in the Hodgkin-Huxley parameters for the steady state activation (m), the steady state inactivation (h) and the time constants (_m and _h) for activation and inactivation of the sodium current are shown. Them andh curves are shifted in positive and negative directions respectively on the voltage axis. The time constants are not greatly affected. (4) In axons in which the sodium current inactivation had been largely removed by treatment with chloramine T, the sodium current was still reduced by ca. 50% by 1 mM benzocaine and the positive shift in activation remained unchanged. (5) The dependence on benzocaine concentration (for2mM) of the peak sodium current reduction and the shift in steady state inactivation have been determined. (6) It is concluded that in the squid axon the effects on inactivation are not the main reason for the reduction of the sodium current by benzocaine and that, in common with many other neutral anaesthetics, there are at least two sites at which benzocaine acts.     

Effects of Na+, K+ and Mg2+ on45Ca2+ uptake by pancreatic islets

Microdissected pancreatic islets of noninbredob/ob-mice were used to study ionic effects on the lanthanum-nondisplaceable⁴⁵Ca²⁺ uptake by islet cells. Omission of Mg²⁺ from the incubation medium had no effect, but the⁴⁵Ca²⁺ uptake was increased by omission of Na⁺ and decreased by omission of K⁺. Excess Mg²⁺ (1.2–15 mM) inhibited and excess K⁺ (4.7–25 mM) stimulated the⁴⁵Ca²⁺ uptake in a concentration-dependent manner. Stimulation of⁴⁵Ca²⁺ uptake in Na⁺-deficient islets was associated with an enhancement of the basal insulin release. Total abolishment of glucose-stimulated⁴⁵Ca²⁺ uptake in K⁺-deficient islets did not preclude a significant secretory response to glucose. It is concluded that the lanthanum-nondisplaceable⁴⁵Ca²⁺ uptake shows a partial correlation to insulin release.     

阿魏酸钠对大鼠晶状体上皮细胞凋亡相关基因BCl-2和bax的调控

目的:本研究旨在探讨阿魏酸钠 (SF)对实验性氧化损伤大鼠晶状体上皮细胞 (LEC)凋亡相关基因BCl-2和bax的调控。方法:将SD大鼠双眼随机分成空白对照组、过氧化氢 (H₂O₂)组、吡诺克辛 (PS)组和SF组。无菌操作摘除眼球并在手术显微镜下分离晶状体,使晶状体孵育在 300μmol·L^-1H₂O₂ 培养液中复制LEC凋亡模型,同时加入终浓度为 5mmol·L^-1的SF,置二氧化碳培养箱共同孵育 2 4h。取晶状体前囊膜采用免疫组化法检测凋亡相关基因BCl-2和bax的蛋白表达并进行比较。结果:(1)正常SD大鼠LEC中BCl-2和Bax均有表达,BCl-2表达较Bax表达强。 (2)H₂O₂ 组BCl-2表达显著下调,Bax表达显著上调 (Ridit检验,P <0.01);BCl-2 /Bax比率下降。(3)与H₂O₂ 组比较,SF可明显上调BCl-2表达,下调Bax表达 (P <0.01),BCl-2 /Bax比率上升。 (4)PS与SF的调节作用相似,但SF的作用强于PS(P <0.05)。结论:本研究结果表明,SF调控凋亡相关基因BCl-2和bax的表达可能是SF抑制LEC凋亡的分子机制.