Basis of Rise in Intracellular Sodium in Airway Hyperresponsiveness and Asthma

The aim of this study was to investigate the basis of disturbances in sodium transport in asthma and in airway hyperresponsiveness without symptoms of asthma (asymptomatic AHR). We measured the intracellular sodium (Na_i); activity of Na⁺/K⁺-ATPase in unstimulated cells (resting activity) and in cell homogenate under optimal conditions (maximal activity); and sodium influx, in mixed leukocytes of 15 normal subjects, 12 subjects with asymptomatic AHR, and 26 asthmatics with or without active symptoms. Resting Na⁺/K⁺-ATPase activity was the same as sodium influx, consistent with homeostasis. Compared with normal subjects, those with asymptomatic AHR or asthma with controlled symptoms had a twofold increase in sodium influx and Na_i. Symptomatic asthmatics also had a twofold increase in sodium influx but a fourfold elevation of Na_i. Maximal Na⁺/K⁺-ATPase activity was reduced by half in symptomatic asthmatics compared with normal subjects. The reduction of maximal Na⁺/K⁺-ATPase activity was associated with a significant decrease in ATP turnover per Na⁺/K⁺-ATPase molecule but not number of Na⁺/K⁺-ATPase molecules per cell. In summary, airway hyperresponsiveness with or without asthma is associated with increased sodium influx and Na in leukocytes. Resting activity of Na⁺/K⁺-ATPase is also increased as a compensatory response to the increased sodium influx, but it is achieved at the expense of higher Na_i. Symptomatic asthma is additionally associated with reduction in maximal activity of Na⁺/K⁺-ATPase, resulting in reduced capacity to handle the increase in sodium influx and consequent severe elevations in Na_i.     

Peroxynitrite induced decrease in Na^＋, K^＋-ATPase activity is restored by taurine

AIM: Peroxynitrite (ONOO-) is a powerful oxidant shown to damage membranes. In the present study, the effect of taurine on changes of liver plasma membrane Na+, K+-ATPase induced by ONOO- was investigated. METHODS: Liver plasma membrane was exposed to ONOO-with or without taurine. Na+, K+-ATPase activity and lipid peroxidation as thiobarbituric acid reactive substances (TBARS) levels were measured. RESULTS: Different concentrations of ONOO- (100, 200, 500, and 1 000 μmol/L) were found to decrease liver plasma membrane Na+, K+-ATPase activity significantly. The depletion of enzyme activity was not concentration dependent. Effects of different concentrations of taurine on liver plasma membrane Na+, K+-ATPase activity were also measured. Taurine did not cause any increase in enzyme activity. When plasma membranes were treated with 200 μmol/L ONOO- with different concentrations of taurine, a restoring effect of taurine on enzyme activity was observed. TBARS levels were also measured and taurine was found to decrease the elevated values. CONCLUSION: Taurine is observed to act as an antioxidant of ONOO- to decrease lipid peroxidation and thus affect liver plasma membrane Na+, K+-ATPase by restoring its activity.     

Ruthenium red reduces the Ca2+ sensitivity of Ca2+ uptake into cardiac sarcoplasmic reticulum

 Ruthenium red inhibits mitochondrial Ca²⁺ uptake and is widely used as an inhibitor of ryanodine-sensitive Ca²⁺ channels that function to release Ca²⁺ from the sarcoplasmic reticulum (SR) of muscle cells. It also has effects on other Ca²⁺ channels and ion transporters. To study the effects of ruthenium red on Ca²⁺ transport into the SR of cardiac muscle cells, fluorescence measurements of Ca²⁺ uptake into cardiac SR vesicles were made. Ruthenium red significantly decreased the Ca²⁺ sensitivity of SR uptake in a dose-dependent manner at concentrations ranging from 5 μM to 20 μM. There were no significant effects of ruthenium red on the maximum velocity or the Hill coefficient of SR Ca²⁺ uptake. Received: 14 January 1998 / Received after revision: 12 March 1998 / Accepted: 16 March 1998     

Selective sensitivity of synaptosomal membrane function to cerebral cortical hypoxia in newborn piglets

The effect of hypoxia on the structure and function of the synaptosomal membranes and myelin fraction (glial cells, neuronal cell bodies and axonal membranes) was investigated by measuring Na⁺,K⁺-ATPase activity and levels of lipid peroxidation products in cerebral cortical synaptosomal membranes and myelin fractions obtained from newborn piglets. Hypoxic hypoxia was induced and cerebral hypoxia was documented as a decrease in the ratio of phosphocreatine to inorganic phosphate (PCr/Oi) using³¹P-NMR spectroscopy. PCr/Pi decreased from baseline of2.93 ± 0.76to0.61 ± 0.36 during hypoxia. The synaptosomal membrane Na⁺,K⁺-ATPase activity decreased from a control value of56.6 ± 3.7to40.4 ± 6.0 μgmol Pi/mg protein/h during hypoxia. The level of conjugated dienes increased from zero (reference value) to4.5 ± 2.7 nmol/mg lipid and the level of fluorescent compounds increased from23.5 ± 2.2to92.6 ± 46.4 ng quinine sulfate/mg lipid in the synaptosomal membranes during hypoxia. No change in myelin fraction Na⁺,K⁺-ATPase activity or levels of lipid peroxidation products were noted. These data indicate that sunaptosomal membranes, rich in polyunsaturated fatty acids, are more susceptible to oxygen free radical mediated lipid peroxidative damage during hypoxia.     

青蒿总香豆素解热作用及其机理初步研究

目的:研究青蒿总香豆素解热(降温)作用并探讨其作用机理。方法:从黄花蒿中提取总香豆素,利用内生致热原性家兔发热模型,观察青蒿总香豆素对发热家兔体温的影响并测定脑脊液、血清中前列腺素E₂(PGE₂)、环单磷酸腺苷(cAMP)水平以及肝脏、腓肠肌钠泵活性。结果:青蒿总香豆素可以显著降低正常及发热家兔体温,抑制肝脏、腓肠肌组织钠泵活性,降低发热家兔血液及脑脊液PGE₂水平,对血液及脑脊液cAMP水平变化无明显影响。结论:香豆素成分可能是青蒿解热降温的有效部位,其作用机制与抑制钠泵活性及降低中枢PGE₂水平有关。     

问荆碱对大鼠脑囊泡膜Mg2+-ATPase,Ca2+-ATPase抑制作用的动力学研究

问荆碱对大鼠脑囊泡膜Mg²⁺-ATPase,Ca²⁺-ATPase有显著的抑制作用,对Mg²⁺-ATPase的抑制机制分别为竞争性抑制(Mg²⁺,Ki=4.93×10^-5mol/L)、非竞争性抑制(ATP,Ki=1.06×10^-4mol/L),对Ca²⁺-ATPase的抑制机制分别为混合型抑制(Ca²⁺,Ki=5.07×10^-5mol/L)、非竞争性抑制(ATP,Ki=3.27×10-4mol/L)。     

Changes in gene expression for GH/PRL/SL family hormones in the pituitaries of homing chum salmon during ocean migration through upstream migration

Gene expression for growth hormone (GH)/prolactin (PRL)/somatolactin (SL) family hormones in the pituitaries of homing chum salmon were examined, because gene expression for these hormones during ocean-migrating phases remains unclear. Fish were collected in the winter Gulf of Alaska, the summer Bering Sea and along homing pathway in the Ishikari River-Ishikari Bay water system in Hokkaido, Japan in autumn. The oceanic fish included maturing adults, which had developing gonads and left the Bering Sea for the natal river by the end of summer. The absolute amounts of GH, PRL and SL mRNAs in the pituitaries of the maturing adults in the summer Bering Sea were 5- to 20-fold those in the winter Gulf of Alaska. The amount of GH mRNA in the homing adults at the coastal seawater (SW) areas was smaller than that in the Bering fish, while the amount of PRL mRNA remained at the higher level until fish arrived at the Ishikari River. The gill Na⁺,K⁺-ATPase activity in the coastal SW fish and the plasma Na⁺ levels in the brackish water fish at the estuary were lowered to the levels that were comparable to those in the fresh water (FW) fish. In conclusion, gene expression for GH, PRL and SL was elevated in the pituitaries of chum salmon before initiation of homing behavior from the summer Bering Sea. Gene expression for GH is thereafter lowered coincidently with malfunction of SW adaptability in the breeding season, while gene expression for PRL is maintained high until forthcoming FW adaptation.     

Age-Dependent Alterations in Na+,K+-ATPase Activity in the Central Nervous System of Spontaneously Hypertensive Rats: Relationship to the Development of High Blood Pressure

We have previously demonstrated that cerebroventricular administrations (i.c.v) of potassium chloride solutions (KCl; 0.375–1.25 μmoles/5 μl) elicit ouabain-sensitive, concentration-dependent decreases in the blood pressure and heart rates of anesthetized, normotensive Sprague-Dawley (SD) rats. These studies have suggested an inverse relationship between Na⁺-pump activity in the central nervous system (CNS) and central sympathetic outflow. Such a view is further supported by the present studies showing that i.c.v. injections of KCl failed to produce any alterations in the blood pressures of rats pretreated with an autonomic ganglionic blocker, chlorisondamine. In the present studies, depressor responses to i.c.v. potassium chloride were considered as functional indices for evaluation of neuronal Na⁺-pump activity in 8 and 12 week old (8 wk and 12 wk) SHR, WKY and Sprague-Dawley (SD) rats. Basal arterial blood pressures of 8 wk-old SD and SHR, and the responsiveness of these two groups to i.c.v. potassium chloride solutions are similar and they both are significantly greater than that of age matched WKY However, in the 12 wk-old groups, arterial pressure of SHR was significantly greater than that of WKY as well as SD, whereas the depressor responses to KCl in SHR were significantly greater than that of only WKY. Pretreatment of the rats with i.c.v. ouabain abolished the differences in the hypotensive responses to i.c.v. potassium chloride that existed between various groups but not the differences in the basal blood pressures. Evaluation of these data suggest that a) the centrally mediated hypotensive responses to K⁺ in various groups could depend upon Na⁺,K⁺-pump activity in C.N.S. and/or on basal central sympathetic discharge; b) central sympathetic activity is greater in SHR only when compared to WKY but not to SD; c) since the central Na⁺-pump activity and sympathetic tone appears to be similar in SHR and SD, mecahnisms other than the increases in sympathetic activity must play a prominent role in the development of spontaneous hypertension; d) attenuation of neuronal Na⁺-pump activity cannot account for greater sympathetic tone in SHR and SD-rats when compared to WKY.     

Membrane potentials in Rana temporaria muscle fibres in strongly hypertonic solutions

Conventional microelectrode methods were used to measure variations in resting membrane potentials, E _m, of intact amphibian skeletal muscle fibres over a wide range of increased extracellular tonicities produced by inclusion of varying extracellular concentrations of sucrose. Moderate increases in extracellular tonicity to up to 2.6× normal (2.6τ) under Cl⁻ free conditions produced negative shifts in E _m that followed expectations for the K⁺ Nernst equation (E _K) applied to a perfect osmometer containing a conserved intracellular K⁺ content despite any accompanying cell volume change. In contrast, E _m remained stable in fibres studied in otherwise similar Cl⁻ containing solutions, consistent with E _m stabilization despite negative shifts in E _K through inward cation-Cl⁻ co-transport activity. Short exposures to higher tonicities (>3τ) similarly produced negative shifts in E _m in Cl⁻ free but not Cl⁻ containing solutions. However, prolonged exposures to solutions of >3τ caused gradual net positive changes in E _m in both Cl⁻ containing and Cl⁻ free solutions suggesting that these changes were independent of cation-Cl⁻ transport. Indeed, there was no evidence of cation-Cl⁻ co-transport activity in strongly hypertonic solutions despite its predicted energetic favourability, suggesting its possible regulation by E _m in muscle. Additional findings implicated a failure to maintain greatly increased transmembrane [K⁺] gradients in these E _m changes. Thus: (1) halving or doubling [K⁺]_e produced negative or positive shifts␣in E _m, respectively in isotonic or moderately hypertonic (<2.7τ), but not strongly hypertonic (>3τ) solutions; (2) subsequent restoration of isotonic extracellular conditions produced further positive changes in E _m consistent with a dilution of the depleted [K⁺]_i by fibres regaining their original resting volumes; (3) quantitative modelling similarly predicted a gradual net efflux of K⁺ as the balance between active and passive [K⁺] fluxes altered due to increased transmembrane [K⁺] gradients in hypertonic and low [K⁺]_e solutions. However, the observed positive changes in E _m in the most strongly hypertonic solutions eventually exceeded these predictions suggesting additional limitations on␣Na⁺/K⁺-ATPase activity in strongly hypertonic solutions.James A. Fraser and Kai Yuen Wong have equally contributed to this paper.     

Reconstitution of phospholipid translocase activity with purified Drs2p,a type-IV P-type ATPase from budding yeast

Type-IV P-type ATPases (P4-ATPases) are putative phospholipid translocases, or flippases, that translocate specific phospholipid substrates from the exofacial to the cytosolic leaflet of membranes to generate phospholipid asymmetry. In addition, the activity of Drs2p, a P4-ATPase from Saccharomyces cerevisiae, is required for vesicle-mediated protein transport from the Golgi and endosomes, suggesting a role for phospholipid translocation in vesicle budding. Drs2p is necessary for translocation of a fluorescent phosphatidylserine analogue across purified Golgi membranes. However, a flippase activity has not been reconstituted with purified Drs2p or any other P4-ATPase, so whether these ATPases directly pump phospholipid across the membrane bilayer is unknown. Here, we show that Drs2p can catalyze phospholipid translocation directly through purification and reconstitution of this P4-ATPase into proteoliposomes. The noncatalytic subunit, Cdc50p, also was reconstituted in the proteoliposome, although at a substoichiometric concentration relative to Drs2p. In proteoliposomes containing Drs2p, a phosphatidylserine analogue was actively flipped across the liposome bilayer to the outer leaflet in the presence of Mg²⁺-ATP, whereas no activity toward the phosphatidylcholine or sphingomyelin analogues was observed. This flippase activity was mediated by Drs2p, because protein-free liposomes or proteoliposomes reconstituted with a catalytically inactive form of Drs2p showed no translocation activity. These data demonstrate for the first time the reconstitution of a flippase activity with a purified P4-ATPase.