Divalent cation inhibition of barley root plasma membrane-bound Ca2+-ATPase activity and its reversal by monovalent cations

The inhibitory action of divalent cations on the Ca²⁺-ATPase activity of a plasma membrane-rich microsome fraction isolated from the roots of barley ( Hordeum vulgare L. cv. Conquest) was investigated. Using electron paramagnetic resonance spectroscopy to measure cation-induced changes in membrane lipid properties, it was demonstrated that certain divalent cations (Ca²⁺, Cd²⁺, UO²⁺₂) inhibit the Ca²⁺ ATP-ase by restriction of lipid polar head group mobility and not by alteration of membrane surface potential. Monovalent cations which stimulate the Ca²⁺-ATPase of barley roots (Na⁺, K⁺, ethanolamine HCl) can also reverse the Ca²⁺-ATPase inhibition by Cd²⁺. The degree of Na⁺ reversal of Cd²⁺-induced Ca²⁺-ATPase inhibition was influenced by the nature of the anion.     

Effects of Microinjected Cations on the Early Event of Fertilization in the Medaka Egg

Effects of microinjected cations on the early events of fertilization were examined using eggs of Oryzias latipes . Microinjection of either Ca²⁺, Ba²⁺ or Sr²⁺ into the thin cortical cytoplasm induced breakdown of cortical alveoli (vesicles) (CABD) under Ca-Mg-free conditions, but microinjection of Mg²⁺, Mn²⁺ or Co²⁺ prevented CABD at the injected region when the eggs were inseminated in regular saline. Under Ca-Mg-free conditions, CABD could also be induced by microinjection of various solutions (NaCl, choline chloride, sucrose, pH buffer) without any divalent cations or ionophore A23187. Ca²⁺ microinjected into the cortical cytoplasm did not play a role in sperm penetration. Upon microinjection with either Ca²⁺, Mg²⁺ or K⁺, the resting membrane potential leakage was transiently observed. However, depolarization of the membrane followed by slow hyperpolarization was observed only upon microinjection of Ca²⁺. From these experiments, it was inferred that microinjected divalent cations such as Ca²⁺, Ba²⁺ or Sr²⁺ do not act directly upon the cortical alveolus membrane, but trigger the induction of CABD via depolarization of the membrne and increase in intracellular Ca²⁺.     

Magnesium Transport by Brain Mitochondria: Energy Requirement and Dependence on Ca2+ Fluxes

Abstract: The association of Mg²⁺ ions with mitochondria isolated from guinea pig cerebral cortex is investigated and resolved into two components, that bound to the surface of both the outer and the inner membranes and that transported into the mitochondrial matrix. When rotenone-treated mitochondria are preincubated in a Mg²⁺ -containing medium, Mg²⁺ binding can be measured and actual Mg²⁺ transport determined after the addition of succinate. Mg²⁺ uptake as well as retention within mitochondria is an energy-dependent process linked to substrate oxidation. EGTA completely prevents Mg²⁺ uptake, while the Ca²⁺ uniporter inhibitor Ruthenium Red, along with prevention of Mg²⁺ uptake, induces a slow efflux of accumulated Mg²⁺ ions. These findings suggest that both inward and outward Mg²⁺ movements follow Ca²⁺ fluxes across the mitochondrial membrane. Modulation of Mg²⁺ movements by mitochondria is therefore suggested to occur within nerve terminals.     

Effect of calcium and other metal ions on pectic activities from autolysed cultures of Alternaria alternata

Abstract The effect of increasing concentrations of Ca²⁺, Mg²⁺, Cu²⁺, Zn²⁺, Na⁺ and EDTA on the pectic enzymic activities (polymethylgalacturonase, endopectinase and pectin-lyase) present in the autolytic complex from Alternaria alternata has been studied. In all cases the divalent metal ions and EDTA produced an increased inhibition correlated with increasing concentration of each ion. An opposite effect was shown by the Na⁺ ion, which produced an increase in pectic enzymic activities, principally at low concentrations.     

Comparison of ion transportation before and after egg hatching in Amphinemura sp. (Plecoptera)

Abstract.  An increase in egg size with embryonic development in stoneflies is believed to result from the uptake of water by osmosis. The present study aims to investigate whether a selective ion transport through egg membranes exists before hatching, and whether ions are released after hatching. Viable and nonviable egg masses are incubated in Petri dishes filled with water, and the concentrations of the ions F⁻, Cl⁻, SO₄²⁻, NO₃⁻, Na⁺, K⁻, Mg²⁺ and Ca²⁺ in the water are determined. The ion transport of an egg mass before and after hatching and a nonviable egg mass is then calculated. Before hatching, Cl⁻, SO₄²⁻, NO₃⁻, Na⁺, Mg²⁺ and Ca²⁺ are taken up from the surrounding water into the inner egg. These ions are selectively taken into the egg. After hatching, Cl⁻, SO₄²⁻, Na⁺, Mg²⁺ and Ca²⁺ are released into the surrounding water. The amount of these ions released after hatching is lower than the amount taken up before hatching. Ions that are not released after hatching are considered to be used in embryonic development.     

The influences of calcium and magnesium ions on the exchange of monovalent cations in Neurospora crassa

Low-K⁺, high-Na⁺ cells of strain RL21a of Neurospora crassa , in steady state with 25 m M Na⁺, were used to study K⁺/Na⁺ exchanges in the presence or absence of Ca²⁺ and Mg²⁺. In the presence of Ca²⁺ and Mg²⁺, a low concentration of K⁺ (0.3 m M ) triggered a rapid exchange, but in the absence of the divalents, a high K⁺ concentration (30 m M ) was required to initiate the exchange at a rapid rate. In the absence of Ca²⁺ and Mg²⁺, K⁺ uptake did not occur at low K⁺ concentration, internal K⁺ did not regulate Na⁺ influx in the presence of external K⁺, and the efflux of Na⁺ proceeded at maximum activity at very low-K⁺ contents.     

BIOCHEMICAL CHARACTERIZATION OF THE NEURON: RIBONUCLEIC ACID COMPOSITION OF THE NEURONAL CELL BODIES

Abstract— The fluorescence of chlorotetracycline (CTC) in the presence of synaptosomes isolated from sheep brain is selectively increased by Ca²⁺ under conditions in which Mg²⁺, Na⁺, K⁺, Li⁺ or choline have only a small effect. The monovalent cations release bound Ca²⁺ from synaptosomes, and this effect is reflected by a decrease in the CTC fluorescence. Under optimal conditions there is a near parallelism between Ca²⁺ and CTC binding to the synaptosomes membranes, and Li⁺ is the monovalent cation tested which interferes the most with the binding of both substances. These results obtained in a predominantly sucrose medium become less distinct when media simulating physiological composition are utilized, which limits the usefulness of the method. Brain mitochondria and myelin also bind Ca²⁺ and CTC. The ratio of the fluorescence signal (or CTC bound) to Ca²⁺ bound is highest of all for mitochondrial membranes, and the apparent fluorescence quantum yield of CTC is also the highest in these membranes, which suggests that the Ca²⁺ in these membranes is localized in a more apolar region than is the case for synaptosomes and myelin.     

DIVALENT CATION-ACTIVATED ECTO-NUCLEOSIDE TRIPHOSPHATASE ACTIVITY OF NERVOUS SYSTEM CELLS IN TISSUE CULTURE

Abstract— Intact neuroblastoma and glial cells in monolayer culture hydrolysed ATP added to their medium. Evidence is presented that ATP is cleaved outside of the permeability barrier of the plasma membrane and the product is liberated in the extracellular medium, i.e. the enzyme is an ecto-enzyme. Divalent cations such as Mg²⁺, Ca²⁺, Mn²⁺ and Co²⁺ activate the enzyme. In neuroblastoma cells, Ca²⁺ is the preferential cation for activation; Mg²⁺ in glial cells. Substrate specificity was very low when different nucleoside-5'-triphosphates were examined. Competition studies have revealed that all of the nucleoside triphosphates are hydrolysed by the same enzyme: divalent cation-activated ecto-nucleoside-5'-triphosphate phosphohydrolase.
Developmental pattern of the enzyme in several lines was established. The role of enzyme in the transport of divalent cations across the plasma membrane and/or in the physical properties of the membrane is suggested.     

Comparative studies of inorganic substances in the blood of fishes from the Scagerac Sea

The concentrations of the main plasma inorganic electrolytes Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl^- and and PO₄^3- have been determined for different orders of marine fishes. For Na⁺ and Cl^- a typical decrease was found when passing from cyclostomes, holocephalans and elasmobranchs to teleosts. The concentrations of K⁺, Ca²⁺ and Mg²⁺ showed a similar trend except that there was a rise in the teleost group, which showed a large range of variation for these three ions. In the case of PO₄^3- no significant differences between groups were found.     

Monovalent—divalent cation ratios and the occurrence of phytoplankton, with special reference to the desmids

SUMMARY. We have analysed data from ninety-nine Scottish freshwater lochs, to explore the relationship between water chemistry and phytoplankton assemblages. Our results confirm that there are strong correlations both between the phytoplankton quotient and divalent cation concentrations, particularly Ca⁺⁺, and also between the phytoplankton quotient and the (Na⁺+ K⁺)/(Ca⁺⁺+ Mg⁺⁺) ratio. However, the latter is evidently a spurious relationship, arising from the former association, together with an association between Ca⁺⁺ and the (Na⁺+K⁺)/ (Ca⁺⁺+ Mg⁺⁺) ratio. The observed correlation does not persist if account is taken of concomitant variations in the Ca⁺⁺concentration. This conclusion is suggested both by relatively informal analyses (median polish, partial correlation coefficients) and by more formal modelling and testing (stepwise regression, all-subsets regression).     

Uptake of metals by bacterial polysaccharides

J.L. GEDDIE AND I.W. SUTHERLAND. 1993. The binding of cations by a range of bacterial polysaccharides was examined. Comparison of native and deacetylated polymers indicated the influence of polysaccharide acetylation on ion uptake and selectivity. The effects of temperature and pH on ion uptake were also examined. Metal ion uptake was carried out by dialysis and samples were analysed using ion chromatography. The native acetylated polymers showed a selectivity for Ca²⁺ > Mg²⁺ > monovalent cations, whereas samples lacking acetyl groups showed a selectivity for monovalent cations > Mg²⁺ > Ca²⁺. Increased temperatures reduced the capacity for several of the polymers to bind the cations; The Zoogloea ramigera polymer appeared least affected. The pH value also affected uptake.     

Changes in Ion Content in Heat-Treated Tetrahymena Cells

SYNOPSIS Changes in the amounts of Na⁺, K⁺, Mg²⁺ and Ca²⁺ were determined in the supernates of homogenized samples of Tetrahymena cells which were exposed to 7 heat shocks. The amounts of the same ions were also determined in the pH 4.5-soluble fractions after dialysis. During the last shock, i.e., 6.5 hr after the start of heat treatment, there was a change in the ion balance characterized by a gain in Na⁺, Ca²⁺ and non-dialyzable Mg²⁺ and a loss of K⁺. The change was not in phase with the synchronous cell division.     

Uptake of Cd2+ and Fe2+ by excised roots of Tamarix aphylla

The uptake of Cd²⁺ by excised roots of Tamarix aphylla (L.) Karst, was investigated using roots of hydroponically grown plants. The concentration isotherm of Cd²⁺ uptake approached saturation with a single phase hyperbola. The time course of Cd²⁺ absorption was generally hyperbolic, with an apparent linear section between 2 and 30 min. The temperature response varied among different temperature ranges: a Q₁₀ of approximately 1.9 was found between 10 and 20°C, but at higher and lower temperatures Q₁₀ values were only 1–1.3. It is concluded that Cd²⁺ uptake by the roots of T. aphylla at moderate temperatures is mediated by a metabolic process, combined with a passive influx component that becomes dominant at higher and lower temperatures. The distribution of the absorption sites for Cd²⁺ and for Fe²⁺ along the roots of T. aphylla was also investigated. Cadmium uptake showed no apparent pattern, whereas a distinct pattern of uptake was observed for Fe²⁺, with the highest rates at the root tip. Iron absorption was stimulated in the presence of nutrients, whereas that of Cd²⁺ was inhibited. Adsorption and absorption of Cd²⁺ were strongly inhibited by Ca²⁺ and by Mg²⁺, but were unaffected by Fe²⁺. Monovalent ions (Na⁺, K⁺, Li⁺) also reduced Cd²⁺ absorption, but to a lesser extent than Ca²⁺ and Mg²⁺. Uptake of Cd⁺ was reduced at lower pH of the medium. The importance of interfering cations for Cd²⁺ tolerance of T. aphylla is emphasized.     

Pb and Cd uptake in rice roots

Pb and Cd are heavy metal pollutants that inhibit plant growth. Using a cultivated rice variety (Dongjin, Oryza sativa L.), we studied how the transport and toxicity of Pb²⁺ and Cd²⁺ are affected by the presence of K⁺, Ca²⁺ or Mg²⁺. K⁺ had a little effect on uptake or toxicity of Pb²⁺ and Cd²⁺. Ca²⁺ or Mg²⁺ blocked both Cd²⁺ transport into rice roots and Cd²⁺ toxicity on root growth, which suggested that their detoxification effect is directly related to their blocking of entry of the heavy metals. Similarly, Ca²⁺ blocked both Pb²⁺ transport into the root and Pb²⁺ toxicity on root growth. The protective effect of Ca²⁺ on Pb²⁺ toxicity may be related to its inhibition of the heavy metal accumulation in the root tip, a potential target site of Pb²⁺ toxicity. Mg²⁺ did not ameliorate the Pb²⁺ toxicity on root growth as much as Ca²⁺ did, although it decreased Pb²⁺ uptake into roots similarly as Ca²⁺ did. These results suggest that the protective effect of Ca²⁺ on Pb²⁺ toxicity may involve multiple mechanisms including competition at the entry level, and that Pb²⁺ and Cd²⁺ may compete with divalent cations for transport into roots of rice plants.     

Renal excretion in channel catfish following injection of quinaldine sulphate or 3- trifluoromethyl-4-nitrophenol

Channel catfish, Ictalurus punctatus Rafinesque, injected intraperitoneally with 2-methyl-quinoline sulphate (QdSO₄) or 3-trifluoromethyl-4-nitrophenol (TFM) eliminate most of the dose of these compounds by extra-renal routes. Patterns of renal excretion of Na⁺, K⁺, Ca²⁺, Mg²⁺, and Cl⁻ (ρEq kg⁻¹ h⁻¹) appeared to be associated with the 'stress' of the urine collection technique rather than with the elimination of either compound. Concentrations of Na⁺, K⁺, Ca²⁺, Mg²⁺, and Cl⁻ (mEq/1) were determined in urine, plasma and gall bladder bile.     

Regional Calcium Accumulation and Cation Shifts in Rat Brain by Kainate

Abstract: Following local application of kainic acid, changes in the contents of Na⁺, K⁺, Ca²⁺, and Mg²⁺ of the striatum, cerebellum, and hippocampus of the rat were observed at various times after surgery. Within 1 h the levels of K⁺ decreased 20% whereas the levels of Na⁺ and Ca²⁺ increased at least 50% and 20%, respectively. These changes persisted for more than 8 weeks. Ca²⁺ levels rose further, to more than 10-fold during 8 weeks. The Mg²⁺ levels were slightly and only transiently decreased. Unilateral injections of kainate into the striatum affected the contents of these cations not only in this area, but also in the overlying cerebral cortex, the olfactory tubercle, and the ipsilateral substantia nigra. The Ca²⁺ increases were less when rats were kept on a diet deficient in Ca²⁺ and vitamin D. ⁴⁵Ca²⁺, intravenously administered, accumulated significantly more in the kainate-lesioned striatum and substantia nigra than in the homotopic contralateral areas. Electron microscopic examination of the localization of Ca²⁺ with the oxalate-pyroantimonate technique showed the appearance of extracellularly located deposits and the accumulation of Ca²⁺ in (possibly degenerating) myelinated axons in kainate-lesioned striata. This study provides evidence that calcification of cerebral tissue is closely associated with neurodegenerative processes and shows that kainate may serve as a tool to elucidate the mechanism of brain calcification. The results are discussed in relation to idiopathic calcinosis (striopallidodentate calcinosis, Fahr's disease).     

Nitroprusside and Cyclic GMP Stimulate Na+-Ca2+ Exchange Activity in Neuronal Preparations and Cultured Rat Astrocytes

Abstract: The effects of nitric oxide (NO)-generating agents on ⁴⁵Ca²⁺ uptake in rat brain slices and cultured rat astrocytes were studied in the presence of monensin, which is considered to drive the Na⁺-Ca²⁺ exchanger in the reverse mode. Sodium nitroprusside (SNP) at >10 µ M increased monensin-stimulated Ca²⁺ uptake in the slices, although it did not affect high K⁺-stimulated Ca²⁺ uptake. Another NO donor, 3-morpholinosydnonimine, was effective. The effect of SNP was antagonized by hemoglobin (50 µ M ), a NO scavenger, and mimicked by 8-bromo-cyclic GMP (100 µ M ). In rat brain synaptosomes, SNP increased monensin-stimulated Ca²⁺ uptake, but it did not affect high K⁺-stimulated Ca²⁺ uptake. 8-Bromocyclic GMP, but not SNP, increased Na⁺-dependent Ca²⁺ uptake significantly in synaptic membrane vesicles in the absence of monensin. In cultured rat astrocytes, SNP and 8-bromo-cyclic GMP increased Ca²⁺ uptake in the presence of ouabain and monensin, which were required for the Ca²⁺ uptake in the cells. These findings suggest that NO stimulates the Na⁺-Ca²⁺ exchanger in neuronal preparations and astrocytes in a cyclic GMP-dependent mechanism.     

Apoplastic pH and inorganic ion levels in tomato fruit: A potential means for regulation of cell wall metabolism during ripening

Apoplastic pH and ionic conditions exert strong influence on cell wall metabolism of many plant tissues; however, the nature of the apoplastic environment of ripening fruit has been the subject of relatively few studies. In this report, a pressure-bomb technique was used to extract apoplastic fluid from tomato fruit ( Lycopersicon esculentum Mill.) pericarp at several developmental stages. pH and the levels of K⁺, Na⁺, Ca²⁺, Mg²⁺, Cl⁻ and P were determined and compared with the values for the bulk pericarp and locule tissues. The pH of the apoplastic fluid from pericarp tissue decreased from 6.7 in immature and mature-green fruits to 4.4 in fully-ripe fruit. During the same period, the K⁺ concentration increased from 13 to 37 m M . The levels of Na⁺ and divalent cations did not change, whereas the anions P and Cl⁻ increased in ripe fruit. Ca²⁺ levels remained relatively constant during ripening at 4–5 m M , concentrations that effectively limit pectin solubilization. The electrical conductivity of the apoplastic liquid increased 3-fold during ripening, whereas osmotically active solutes increased 2-fold. Pressure-treated fruit retained the capacity to ripen. The decline in apoplastic pH and increase in ionic strength during tomato fruit ripening may regulate the activity of cell wall hydrolases. The potential role of apoplastic changes in fruit ripening and softening is discussed.     

Effect of Mg2+ and Ca2+ on the response to nickel toxicity in a serpentine endemic and nickel-accumulating species

The effect of Ca²⁺, Mg³⁺ and Ni²⁺ on root elongation was studied in Alyssum bertolonii Desv., a nickel-accumulating and serpentine endemic species. The results confirm the detoxifying action of Ca²⁺ which reduces the toxic effect of Mg²⁺ and Ni²⁺ on root development. In addition, Ca²⁺ and Mg²⁺ interact positively in depressing Ni²⁺ uptake. The combined effect of these two ions is of relevance for the mechanism of nickel tolerance in A. bertolonii.     

Ontogenesis of Ca++ and Mg++ Contents of Embryonic Chick Heart

The Ca⁺⁺ and Mg⁺⁺ contents of embryonic chick heart were studied by atomic absorption spectrophotometry during a period from 48 h of foetal development until 2-3 days post-hatching. The hearts were isolated and incubated for 40 min at 22°C in three different media aerated with 95% 0₂-5% C0₂. The media included: normal Ringer's; Ca⁺-free Ringer's with 3 mM EGTA; and Ca⁺⁺-free Ringer's with 3 mM EDTA. At 48 h, the tubular myocardium contained 7-3 mM Ca⁺⁺ per wet weight which decreased rapidly to 1-2 mM by 10 days of development and remained between 0-9 and 1-1 mM until hatching. The Ca⁺⁺ content paralleled the changes in Na⁺ content reported earlier. Treatment with excess chelators, EGTA or EDTA, resulted in removal of 65-75% of the Ca⁺⁺ content throughout development until the time of hatching, when 50% of the Ca⁺⁺ became firmly bound. In contrast to the results with Ca⁺⁺, myocardial Mg⁺⁺ content rose rapidly from an initial value of 3.2 mM at 48 h to 6.7 mM by the 5th day of development, and then gradually declined throughout the remaining foetal development to 4.8 mM 2-3 days post-hatching. The Mg⁺⁺ contents closely paralleled changes in K⁺ content during development, which were reported earlier. Treatment with EGTA and EDTA removed 13-22% and 19-28% of the myocardial Mg⁺⁺, respectively, during development until just prior to hatching, when only 10-12% could be removed by chelation.