铜、铅、镉、锌、汞和银离子复合污染对水螅的急性毒性效应

以水螅(Hydrasp)为例,通过单因子静态急性毒性试验方法和等毒性溶液法,分别研究Hg2 、Cu2 、Cd2 、Ag 、Zn2 和Pb2 对其单一和复合毒性效应。单一实验结果表明,它们对水螅毒性大小顺序为Hg2 >Cu2 >Cd2 >Ag >Zn2 >Pb2 。复合毒性实验表明,Zn2 与Cu2 、Hg2 、Pb2 、Ag ;Pb2 与Cu2 ;Hg2 与Ag ;Pb2 与Ag 这些组合对水螅联合急性毒性总体上表现出拮抗作用,Cd2 与Cu2 、Hg2 、Pb2 、Ag 组合总体上则是协同作用,Zn2 与Cd2 、Pb2与Hg2 、Cu2 与Hg2 ,Ag 在不同的浓度水平组合下明显表现出不同的毒性效应。     

The Na+-K+-pump, energy metabolism, and obesity

In intact soleus and extensor digitorum longus muscles obtained from lean and obese mice, the number of [³H]-ouabain binding sites showed no significant difference. In the same muscles obtained from obese mice, the Na⁺-K⁺-pump mediated [⁴²K]-uptake was respectively 39 and 33% larger than in those of lean littermates. This together with the earlier observation that intact muscles require at most 6% of their basal energy production for active Na⁺-K⁺-transport indicates that this process is of no quantitative importance for development of obesity.     

Activity coefficients of the peptide and the electrolyte in ternary systems water+glycylglycine+NaCl, +NaBr, +KCl and +KBr at 298.2 K

The activity coefficients of glycylglycine in four aqueous electrolyte solutions (+NaCl, +NaBr, +KCl and +KBr) were obtained at 298.2 K. The mean ionic activity coefficient of the electrolyte in aqueous solutions containing the peptide was determined from measurements of the potential differences of a cation and an anion ion-selective-electrode, each vs. a double junction reference electrode. The results show that the nature of the anion has a major effect on the activity coefficients of glycylglycine. Comparison of activity coefficient data for glycylglycine with literature data for glycine, both in aqueous NaCl solutions, indicates that the effect of the electrolyte is larger for the peptide than for the amino acid. For the peptide, in all cases, the effect of the electrolyte is more important at low molalities of the electrolyte. The Wilson equation was used to correlate the activity coefficient data obtained. The correlation results were satisfactory for the region of concentrated electrolyte.     

Red cell ouabain binding sites, Na+K+-ATPase, and intracellular Na+ as individual characteristics

Healthy male volunteers were infused for three hours with either a dopamine hydrochloride solution at a rate of 4 ug/kg/min or with normal saline. Plasma amine oxidase and platelet MAO activity towards benzylamine both increased in response to intravenous dopamine. There was no increase in enzyme activity when dopamine was added to the platelet and plasma enzymes in vitro. This heretofore unreported increase in the oxidative deaminating capacity of the human organism may represent an adaptive physiologic response to the high circulating levels of dopamine and provides further evidence for a possible functional significance of these enzymes in man.     

Effect of anoxia on intracellular ATP, Na+i, Ca2+i, Mg2+i, and cytotoxicity in rat hepatocytes.

The effects of anoxia were studied in freshly isolated rat hepatocytes maintained in agarose gel threads and perfused with Krebs-Henseleit bicarbonate buffer (KHB). Cytosolic free calcium (Ca2+i) was measured with aequorin, intracellular sodium (Na+i) with SBFI, intracellular pH (pHi) with BCECF, lactic dehydrogenase (LDH) by the increase in NADH absorbance during lactate oxidation to pyruvate, ATP by 31P NMR spectroscopy in real time, and intracellular free Mg2+ (Mg2+i) from the chemical shift of beta-ATP relative to alpha-ATP in the NMR spectra. Anoxia was induced by perfusing the cells with KHB saturated with 95% N2, 5% CO2. After 1 h of anoxia, beta-ATP fell 66%, and 85% after 2 h, while the Pi/ATP ratio increased 10-fold from 2.75 to 28.3. Under control conditions, the resting cytosolic free calcium was 127 +/- 6 nM. Anoxia increased Ca2+i in two distinct phases: a first rise occurred within 15 min and reached a mean value of 389 +/- 35 nM (p less than 0.001). A second peak reached a maximum value of 1.45 +/- 0.12 microM (p less than 0.001) after 1 h. During the first hour of anoxia, Na+i increased from 15.9 +/- 2.4 mM to 32.2 +/- 1.2 mM (p less than 0.001), Mg2+i doubled from 0.51 +/- 0.05 to 1.12 +/- 0.01 mM (p less than 0.001), and pHi decreased from 7.41 +/- 0.03 to 7.06 +/- 0.1 (p less than 0.001). LDH release doubled during the first hour and increased 6-fold during the second hour of anoxia. Upon reoxygenation, ATP, Ca2+i, Mg2+i, Na+i, and LDH returned near the control levels within 45 min. To determine whether the increased LDH release was related to the rise in Ca2+i, and whether the increased Ca2+i was caused by Ca2+ influx, the cells were perfused with Ca(2+)-free KHB (+ 0.1 mM EGTA) during the anoxic period. After 2 h of anoxia in Ca(2+)-free medium, beta-ATP again fell 90%, but Ca2+i, after the first initial peak, fell below control levels, and LDH release increased only 2.7-fold. During reoxygenation, Ca2+i, ATP, Na+i, and LDH returned near the control levels within 45 min. These results suggest that the rise in Ca2+i induced by anoxia is caused by an influx of Ca2+ from the extracellular fluid, and that LDH release and cell injury may be related to the resulting rise in Ca2+i.     

Effects of phalloidin on K+-dependent, Ca2+-independent neurotransmitter efflux and K+-facilitated, Ca2+-dependent neurotransmitter release.

Phalloidin tightly binds to actin and converts soluble actin into depolymerization-resistant actin filaments. Phalloidin promotes the potassium-dependent, calcium-independent efflux of γ-amino butyric acid and nore-pinephrine from synaptosomes but inhibits the potassium-facilitated, calcium-dependent release of these neurotransmitters. This suggests that an actomyosin system is involved in synaptic transmission.     

The luminal Ca2+ chelator,TPEN, inhibits NAADP-induced Ca2+ release

The regulation of Ca²⁺ release by luminal Ca²⁺ has been well studied for the ryanodine and IP₃ receptors but has been less clear for the NAADP-regulated channel. In view of conflicting reports, we have re-examined the issue by manipulating luminal Ca²⁺ with the membrane-permeant, low affinity Ca²⁺ buffer, TPEN, and monitoring NAADP-induced Ca²⁺ release in sea urchin egg homogenate. NAADP-induced Ca²⁺ release was almost entirely blocked by TPEN (IC₅₀ 17–25 μM) which suppressed the maximal extent of Ca²⁺ release without altering NAADP sensitivity. In contrast, Ca²⁺ release via IP₃ receptors was 3- to 30-fold less sensitive to TPEN whereas that evoked by ionomycin was essentially unaffected. The effect of TPEN on NAADP-induced Ca²⁺ release was not due to an increase in the luminal pH or chelation of trace metals since it could not be mimicked by NH₄Cl or phenanthroline. The fact that TPEN had no effect upon ionophore-induced Ca²⁺ release also argued against a substantial reduction in the driving force for Ca²⁺ efflux. We propose that, in the sea urchin egg, luminal Ca²⁺ is important for gating native NAADP-regulated two-pore channels.     

Physiological functions of mitochondrial Na+-Ca2+ exchanger,NCLX, in lymphocytes

Roles of mitochondrial Na⁺-Ca²⁺ exchanger, NCLX, were studied in B lymphocytes such as heterozygous NCLX knockout DT40 cells, NCLX knockdown A20 cells, and native mouse spleen B lymphocytes treated with a NCLX blocker, CGP-37157. Cytosolic Ca²⁺ response to B cell receptor stimulation was impaired in these B lymphocytes, demonstrating importance of mitochondria-ER Ca²⁺ recycling via NCLX and sarco/endoplasmic reticulum Ca²⁺-ATPase SERCA, and interaction with store-operated Ca²⁺ entry. NCLX was also associated with motility and chemotaxis of B lymphocyte. Contrary to B lymphocytes, contribution of NCLX in mouse spleen T lymphocytes was minor.     

Relationships between Ca2+ release, Ca2+ cycling, and Ca2+-mediated permeability changes in mitochondria

Ruthenium red and/or EGTA prevent cyclic uptake and release of Ca2+ in mitochondria. These compounds inhibit but do not prevent the swelling of liver mitochondria induced by Ca2+ plus t-butyl hydroperoxide or Ca2+ plus N-ethylmaleimide. Ruthenium red and/or EGTA have complex effects on the release rate of Ca2+ and other cations induced by t-butyl hydroperoxide or N-ethylmaleimide. To determine the relationship between permeability changes and Ca2+ release in the absence of Ca2+ cycling, a novel method of data collection and analysis is developed which allows the relative time courses of Ca2+ release and Mg2+ release or swelling to be accurately and quantitatively compared. This method eliminates errors in time course comparisons which arise from the aging of mitochondrial preparations and allows data from different preparations to be directly contrasted. Using the method, it is shown that permeability changes caused by Ca2+-releasing agents are not secondary effects arising from Ca2+ cycling between uptake and release carriers. In the absence of Ca2+-cycling inhibitors, Ca2+ release induced by t-butyl hydroperoxide or N-ethylmaleimide is, in part, carrier-mediated. In the presence of EGTA and ruthenium red, Ca2+ release induced by either agent is mediated solely by the permeability pathway. No differences are apparent in the solute selectivity of the inner membrane permeability defect induced by Ca2+ plus t-butyl hydroperoxide or Ca2+ plus N-ethylmaleimide. A novel type of Ca2+ release from energized liver mitochondria is reported. This release is induced by EGTA, occurs in the absence of other releasing agents or nonspecific permeability changes, and is rapid (greater than or equal to 50 nmol/min/mg protein).     

Intracellular Cs+ activates the PKA pathway,revealing a fast,reversible, Ca2+-dependent inactivation of L-type Ca2+ current

Inactivation of the L-type Ca²⁺ current (I_CaL) was studied in isolated guinea pig ventricular myocytes with different ionic solutions. Under basal conditions, I_CaL of 82% of cells infused with Cs⁺-based intracellular solutions showed enhanced amplitude with multiphasic decay and diastolic depolarization-induced facilitation. The characteristics of I_CaL in this population of cells were not due to contamination by other currents or an artifact. These phenomena were reduced by ryanodine, caffeine, cyclopiazonic acid, the protein kinase A inhibitor H-89, and the cAMP-dependent protein kinase inhibitor. Forskolin and isoproterenol increased I_CaL by only 60% in these cells. Cells infused with either N-methyl-D-glucamine or K⁺-based intracellular solutions did not show multiphasic decay or facilitation under basal conditions. Isoproterenol increased I_CaL by 200% in these cells. In conclusion, we show that multiphasic inactivation of I_CaL is due to Ca²⁺-dependent inactivation that is reversible on a time scale of tens of milliseconds. Cs⁺ seems to activate the cAMP-dependent protein kinase pathway when used as a substitute for K⁺ in the pipette solution. L-type calcium current; calcium-dependent inactivation; facilitation; phosphorylation; cesium     

Sustained Ca2+ transfer across mitochondria is Essential for mitochondrial Ca2+ buffering,sore-operated Ca2+ entry,and Ca2+ store refilling

Mitochondria have been found to sequester and release Ca2+ during cell stimulation with inositol 1,4,5-triphosphate-generating agonists, thereby generating subplasmalemmal microdomains of low Ca2+ that sustain activity of capacitative Ca2+ entry (CCE). Procedures that prevent mitochondrial Ca2+ uptake inhibit local Ca2+ buffering and CCE, but it is not clear whether Ca2+ has to transit through or remains trapped in the mitochondria. Thus, we analyzed the contribution of mitochondrial Ca2+ efflux on the ability of mitochondria to buffer subplasmalemmal Ca2+, to maintain CCE, and to facilitate endoplasmic reticulum (ER) refilling in endothelial cells. Upon the addition of histamine, the initial mitochondrial Ca2+ transient, monitored with ratio-metric-pericam-mitochondria, was largely independent of extracellular Ca2+. However, subsequent removal of extracellular Ca2+ produced a reversible decrease in [Ca2+]mito, indicating that Ca2+ was continuously taken up and released by mitochondria, although [Ca2+]mito had returned to basal levels. Accordingly, inhibition of the mitochondrial Na+/Ca2+ exchanger with CGP 37157 increased [Ca2+]mito and abolished the ability of mitochondria to buffer subplasmalemmal Ca2+, resulting in an increased activity of BKCa channels and a decrease in CCE. Hence, CGP 37157 also reversibly inhibited ER refilling during cell stimulation. These effects of CGP 37157 were mimicked if mitochondrial Ca2+ uptake was prevented with oligomycin/antimycin A. Thus, during cell stimulation a continuous Ca2+ flux through mitochondria underlies the ability of mitochondria to generate subplasmalemmal microdomains of low Ca2+, to facilitate CCE, and to relay Ca2+ from the plasma membrane to the ER.     

A pungent ingredient of mustard, allylisothiocyanate, inhibits (H+ + K+)-ATPase

Allylisothiocyanate (ANCS) is shown to inhibit (H+ + K+)-ATPase isolated from the parietal cell of hog gastric mucosa. The ATPase is the proton pump in the secretory membrane of the parietal cell and is an essential component of the acid secretory mechanism. Furthermore, ANCS suppresses acid secretion by bullfrog gastric mucosa in vitro. We suggest that one aspect of the stomachic function produced by ANCS-including foods is the suppressive effect of ANCS on the acid secretory mechanism.