Influence of the production system on the surface properties of influenza A virus particles

In this study, influenza A/Puerto Rico/8/34 H1N1 virus particles (VP) produced in adherent and suspension Madin Darby canine kidney cells were investigated with a broad analytical toolbox to obtain more information on the VP's surface properties potentially affecting their aggregation behavior. First, differences in aggregation behavior were revealed by VP size distributions obtained via differential centrifugal sedimentation and confirmed by dynamic light scattering. The VP produced in adherent cells showed increased levels of aggregation in a 20 mM NaCl 10 mM Tris‐HCl pH 7.4 low‐salt buffer. This included the formation of multimers (dimers up to pentamers), whereas VP produced in suspension cells displayed no tendency toward aggregate formation. To investigate the cause of these differences in aggregation behavior, the VP samples were compared based on their zeta potential, their surface hydrophobicity, their lipid composition, and the N‐glycosylation of their major VP surface protein hemagglutinin. The zeta potential and the hydrophobicity of the VP produced in the adherent cells was significantly decreased compared to the VP produced in the suspension cells. The lipid composition of both VP systems was approximately identical. The hemagglutinin of the VP produced in adherent cells included more of the larger N‐glycans, whereas the VP produced in suspension cells included more of the smaller N‐glycans. These results indicate that differences in the glycosylation of viral surface proteins should be monitored to characterize VP hydrophobicity and aggregation behavior, and to avoid aggregate formation and product losses in virus purification processes for vaccines and gene therapy.     

Effect of internal and external K+ on Na+−Ca2+ exchange in dialyzed squid axons under voltage clamp conditions

The effect of external and internal K⁺ on Na_o⁺-dependent Ca²⁺ efflux was studied in dialyzed squid axons under constant membrane potential. With axons clamped at their resting potentials, external K⁺ (up to 70 mM) has no effect on Na⁺?Ca²⁺ exchange. Removal of K_i⁺ causes a marked inhibition in the Na_o⁺-dependent Ca²⁺ efflux component. Internal K⁺ activates the Na⁺?Ca²⁺ exchange with low affinity $\text{(K}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 90 mM)}$. Activation by K_i⁺ is similar in the presence or in the absence of Na_i⁺, thus ruling out a displacement of Na_i⁺ from its inhibitory site. Axons dialyzed with ATP also show a dependency of Ca²⁺ efflux on K_i⁺. The present results demonstrate that K_i⁺ is an important cofactor (partially required) for the proper functioning of the forward Na⁺?Ca²⁺ exchange.     

Acclimation to humic substances prevents whole body sodium loss and stimulates branchial calcium uptake capacity in cardinal tetras Paracheirodon axelrodi (Schultz) subjected to extremely low pH

Kinetics of sodium (Na⁺) and calcium (Ca²⁺) uptake were studied in cardinal tetras Paracheirodon axelrodi acclimated to humic substances (HS, 35 mg C l^?1) and low pH (pH 3·72), parallel to analysis of whole body Na⁺ and Ca²⁺ content. This species had a high uptake capacity (J_max) for both Na⁺ and Ca²⁺ in soft, ion‐poor water. The affinity constant (K_m) did not vary significantly among treatments for either Na⁺ or Ca²⁺. J_max Na⁺ increased 30% in fish acclimated to HS for 5 weeks. Acclimation to low pH had no effect on J_max Na⁺ but this treatment was associated with a 32% decrease on whole body Na⁺ content, suggesting that fish were unable to compensate for the increased Na⁺ loss induced by extreme acidity. Exposure of fish to HS + low pH, the treatment most closely approximating to the conditions experienced by the species in its native environment, resulted in an increase in whole body Na⁺ by 31% relative to acclimation to low pH alone. J_max Ca²⁺ in cardinal tetras was high relative to that documented in other freshwater species acclimated to soft water (J_max= 30 nmol g^?1 h^?1). Prolonged exposure of fish to pH 3·72 inhibited J_max Ca²⁺ by 53%, although whole body Ca²⁺ content remained unchanged relative to control. Acclimation of fish to HS + low pH resulted in an increase of J_max Ca²⁺ by 166% relative to low pH alone. Collectively, these results suggest that HS protect cardinal tetras acclimated to soft, acidic waters by preventing excessive Na⁺ loss (as indicated by whole body Na⁺ content) and by stimulating Ca²⁺ uptake (as indicated by increased J_max Ca²⁺) to ensure proper homeostasis.     

Humic substances and the water calcium content change the toxicity of malachite green

Laboratory experiments were conducted to test interactive effects of calcium (Ca²⁺) content and the presence of humic substance (HS) on malachite green (MAG)‐induced toxicity in fish embryos and larvae by means of a semistatic 144‐h‐embryo‐larval‐test with zebrafish (Danio rerio). Two kinds of reconstituted water samples were used to produce the test media by mixing salts into deionized water resulting in either hard water (↑Ca ? HS), or soft water (↓Ca ? HS). By adding HS two additional test media were produced (↑Ca + HS, ↓Ca + HS). MAG was tested in concentrations of 0.05, 0.10, 0.15, 0.20, 0.25 mg L^?1. The toxicity ranking of MAG (mg L^?1) to embryos based on 96‐h‐LC₅₀ in the different test water samples is: ↑Ca ? HS (0.061) > ↑Ca + HS (0.123) = ↓Ca ? HS (0.12) ≥ ↓Ca + HS (0.134) and on 144‐h‐LC₅₀ to larvae is: ↑Ca ? HS (0.038) > ↑Ca + HS (0.06) > ↓Ca ? HS (0.077) = ↓Ca + HS (0.077). Mortality of all the groups was significantly different (P < 0.05). Increased Ca²⁺ concentrations did not protect zebrafish embryos and larvae from MAG‐induced toxicity. At high Ca²⁺ conditions, the mortality of the embryos as well as of the larvae is reduced in the ↑Ca + HS group relative to the ↑Ca ? HS group. Thus, at high Ca²⁺ conditions the HS does affect the MAG‐induced mortality. The mechanism which causes the higher toxicity of MAG in the presence of higher Ca²⁺ concentrations is poorly understood. A probable explanation could be the stimulation of the calcium‐binding protein calmodulin as well as the calmodulin kinase II in cell membranes in the presence of high Ca²⁺ concentrations.     

The role of Ca<Superscript>2+</Superscript>, H<Superscript>+</Superscript>, and Cl<Superscript>−</Superscript> ions in generation of variation potential in pumpkin plants

The contributions of Ca²⁺, H⁺, and Cl⁻ in generation of variation potentials (VP) in 3- to 4-week-old pumpkin (Cucurbita pepo L., cv. Mozoleevskaya) plants were assessed. During VP generation, transient alkalinization of the medium around the stem was recorded with a potentiometric method. The pH changes were kinetically similar to the electric potential changes and were apparently due to temporal suppression of the plasma-membrane electrogenic H⁺ pump. These data and the observed inhibition of VP in the stem zone treated locally with a metabolic inhibitor (NaN₃) indicate that the VP generation is related to the reversible suppression of the H⁺-pump. The anion channel blocker (ethacrynic acid) decelerated significantly the front slope of VP and reduced the VP amplitude. A short-term increase in external Cl⁻ concentration around the stem was observed during potential transients representing the VP front slope and the pulses integrated into VP. The removal of Ca²⁺ from extracellular medium inhibited the VP generation. It is proposed that Ca²⁺ plays a role in activation of anion channels and in the H⁺-pump inactivation. The VP generation is probably determined by a complex mechanism, with contributions from passive ion fluxes (Ca²⁺, Cl⁻) moving along the electrochemical gradients and from changes in the electrogenic pump activity.     

The ionic components of the current pulses generated by developing fucoid eggs.

Using a newly developed, extracellular vibrating electrode, we studied the ionic composition of the current pulses which traverse the developing Pelvetia embryo. External Na⁺, Mg²⁺, or SO₄^2?, are not needed for the first 20 min of pulsing. In fact, lowering external Na⁺ or Mg²⁺ (or K⁺) actually stimulates pulsing. Since tracer studies show that Ca²⁺ entry is speeded by Na⁺, Mg²⁺, or K⁺ reduction, these findings suggest that Ca²⁺ entry triggers pulsing. A sevenfold reduction in external Cl^? raises pulse amplitudes by 60%. Moreover, Cl^? is the only major ion with an equilibrium potential near the pulse reversal potential. These facts suggest that Cl^? efflux carries much of the “inward” current. We propose a model for pulsing in which increased Ca²⁺ within the growing tip opens Cl^? channels. The resulting Cl^? efflux slightly depolarizes the membrane and thus drives a balancing amount of K⁺ out. Thus, the pulses release KCl and serve to relieve excess turgor pressure. By letting Ca²⁺ into the growing tip, they should also strengthen the transcytoplasmic electrical field which is postulated to pull growth components toward this tip.     

Permeability to ions of bovine retinal disk membrane vesicles in the bleached state

The permeability of the bleached disk membrane of retinal rod outer segments to univalent and divalent ions is studied by light scattering. The membranes are isolated from frozen dark-adapted bovine retinae, swollen into spherical vesicles in a hypotonic medium and bleached in dilute suspension and their size is determined by elastic and quasi-elastic light scatterings. Various electrolytes are then added to the suspending medium in order to examine their osmotic activity relative to the vesicles deformation characteristics. By following the deformation behavior of the membrane vesicles by elastic light scattering in terms of the oblate ellipsoidal shell model, the osmotic activity of a given electrolyte is qualitatively deduced and thereby the permeability of the membrane to the electrolyte is ranked in reference to a chosen standard, i.e., sucrose. By this method, we show that the permeabilities to Na⁺, K⁺, Mg²⁺ and Ca²⁺ are all alike, and those to halides (F^?, Cl^?, Br^?, I^?), nitrate and phosphates (HPO₄^2?/H₂PO₄^?) are similar. Acetate, however, is about 3-times more permeative, while sulfate is less permeative than the other anions by about the same factor. The viability of our method is checked with use of an ionophore, lasolocid (X-537A), by establishing partial recovery from the osmotic deformation through the suppression of the cation osmotic effect. Ion-induced aggregation and pH-dependent size and shape changes are both found to be insignificant.     

Effects of Monovalent and Divalent Cations on Ca2+ Fluxes Across Chromaffin Secretory Membrane Vesicles

Abstract: Bovine chromaffin secretory vesicle ghosts loaded with Na⁺ were found to take up Ca²⁺ when incubated in K⁺ media or in sucrose media containing micromolar concentrations of free Ca²⁺. Li⁺- or choline⁺loaded ghosts did not take up Ca²⁺. The Ca²⁺ accumulated by Na⁺-loaded ghosts could be released by the Ca²⁺ ionophore A23187, but not by EGTA. Ca²⁺ uptake was inhibited by external Sr²⁺, Na ⁺, Li ⁺, or choline ⁺. All the ⁴⁵Ca²⁺ accumulated by Na⁺-dependent Ca²⁺ uptake could be released by external Na ⁺, indicating that both Ca²⁺ influx and efflux occur in a Na⁺-dependent manner. Na ⁺ -dependent Ca²⁺ uptake and release were only slightly inhibited by Mg²⁺. In the presence of the Na⁺ ionophore Monensin the Ca²⁺ uptake by Na ⁺-loaded ghosts was reduced. Ca²⁺ sequestered by the Na⁺-dependent mechanism could also be released by external Ca²⁺ or Sr²⁺ but not by Mg²⁺, indicating the presence of a Ca²⁺/Ca²⁺ exchange activity in secretory membrane vesicles. This Ca²⁺/Ca²⁺ exchange system is inhibited by Mg²⁺, but not by Sr²⁺. The Na ⁺ -dependent Ca²⁺ uptake system in the presence of Mg²⁺ is a saturable process with an apparent K_m of 0.28 μM and a V_max= 14.5 nmol min^?1 mg protein^?1. Ruthenium red inhibited neither the Na⁺/Ca²⁺ nor the Ca²⁺/Ca²⁺ exchange, even at high concentrations.     

A possible involvement of cytoplasmic Ca2+ in sodium dependency of neurite outgrowth of rat pheochromocytoma PC12 cells

The effects of extracellular Na⁺, K⁺ and Cl^? on neurite outgrowth of PC12 pheochromocytoma cells were studied. Nerve growth factor (NGF)-induced neurite formation was inhibited upon substitution of choline chloride for NaCl under normal culture conditions. It was found that neurite formation increased proportionately with the concentration of Na⁺ in medium up to 150 mM. When PC12 cells were exposed to NGF in suspension culture followed by transfer to new dishes, they showed neurite extention in response to NGF in an RNA- and protein synthesis-independent manner. Under these conditions, neurite outgrowth occurred normally in 60–150 mM Na⁺, whereas it decreased significantly at lower concentrations of Na⁺. Na⁺ dependency was also observed for cyclic AMP-mediated neurite formation of PC12 cells. In contrast, neurite outgrowth was independent of K⁺ in the range 5–106 mM, suggesting that membrane potential did not play a role in this process. No alterations were observed in neurite outgrowth with Cl^? replaced by NO^?₃, SO^2?₄, or 2-hydroxyethanesulfonate. Thus, extracellular Na⁺ plays a role in controlling neurite formation of these cells. An attempt was made to relate this effect to a decrease in cytoplasmic Ca²⁺ concentration monitored by a fluorescent dye sensitive to Ca²⁺.     

Rapid calcium exchange for protons and potassium in cell walls of Chara

Net fluxes of Ca²⁺, H⁺ and K⁺ were measured from intact Chara australis cells and from isolated cell walls, using ion-selective microelectrodes. In both systems, a stimulation in Ca²⁺ efflux (up to 100 nmol m^?2 s^?1, from an influx of ～40 nmol m^?2 s^?1) was detected as the H⁺ or K⁺ concentration was progressively increased in the bathing solution (pH 7.0 to 4.6 or K⁺ 0.2 to 10mol m^?3, respectively). A Ca²⁺ influx of similar size occurred following the reverse changes. These fluxes decayed exponentially with a time constant of about 10 min. The threshold pH for Ca²⁺ efflux (pH 5.2) is similar to a reported pH threshold for acid-induced wall extensibility in a closely related characean species. Application of NH₄⁺ to intact cells caused prolonged H⁺ efflux and also transient Ca²⁺ efflux. We attribute all these net Ca²⁺ fluxes to exchange in the wall with H⁺ or K⁺. A theoretical treatment of the cell wall ion exchanges, using the ‘weak acid Donnan Manning’ (WADM) model, is given and it agrees well with the data. The role of Ca²⁺ in the cell wall and the effect of Ca²⁺ exchanges on the measured fluxes of other ions, including bathing medium acidification by H⁺ efflux, are discussed.     

Daily Patterns under the Life Cycle of a Maize Crop

Together with photosynthesis, transpiration and respiration, the daily uptake of NO₃^?, NH₄⁺, H₂PO₄^?, K⁺, Ca²⁺, Mg²⁺, SO₄^2?, the root respiration, root volume increase and root excretions have been studied by daily measurements during the growth period of whole maize plants (Zea mays L. cv. INRA F7 × F2) raised until complete maturity on nutrient solution. The uptake patterns show a maximum absorption of NO₃^?, K⁺ and Ca²⁺ during the vegetative growth phase. The absorption of these ions declines during maturation while that of H₂PO₄^? reaches a maximum. Root respiration and particularly the uptake of NO₃^? and K⁺ are well correlated with the rate of root growth. Root excretion is more notable in young plants than in the old. It represents less than 0.2% of the net assimilation of adult plants.     

Measurements of intracellular ionized calcium in squid giant axons using calcium-selective electrodes

Ca²⁺-selective electrodes have been used to measure free intracellular Ca²⁺ concentrations in squid giant axons. Electrodes made of glass cannulas of about 20 μm in diameter, plugged with a poly(vinyl chloride) gelled sensor were used to impale the axons axially. They showed a Nernstian response to Ca²⁺ down to about 3 μM in solutions containing 0.3 M K⁺ and 0.025 M Na⁺. Sub-Nernstian but useful responses were obtained up to pCa 8. The electrodes showed adequate selectivity to Ca²⁺ over Mg²⁺, H⁺, K⁺ and Na⁺. To calibrate them properly, a set of standard solutions were prepared using different Ca²⁺ buffers (EGTA, HEEDTA, nitrilotriacetic acid) after carefully characterizing their apparent Ca²⁺ association constants under conditions resembling the axoplasmic environment. In fresh axons incubated in artificial seawater containing 4 mM Ca²⁺, the mean resting intracellular ionized calcium concentration was 0.106 μM ($\text{n = 15}$). The Ca²⁺-electrodes were used to investigate effects of different experimental procedures on the [Ca²⁺]_i. The main conclusions are: (i) intact axons can extrude calcium ions at low [Ca²⁺]_i levels by a process independent of external Na⁺; (ii) poisoned axons can extrude calcium ions at high levels of [Ca²⁺]_i by an external Na⁺-dependent process. The level of free intracellular Ca attained at these latter conditions is about an order to magnitude greater than the resting physiological value.     

KCl loss and cell shrinkage in the ehrlich ascites tumor cell induced by hypotonic media, 2-deoxyglucose and propranolol

Ehrlich ascites tumor cells lose KCl and shrink after swelling in hypotonic media and in response to the addition of 2-deoxyglucose, propranolol, or the Ca²⁺ ionophore, A23187, plus Ca²⁺ in isotonic media. All of these treatments activate cell shrinkage via a pathway with the following characteristics: (1) the KCl loss responsible for cell shrinkage does not alter the membrane potential; (2) NO₃^? does not substitute for Cl^?; (3) the net KCl movements are not inhibited by quinine or DIDS; and (4) early in this study furosemide was effective in inhibiting cell shrinkage but this sensitivity was subsequently lost. This evidence suggests that the KCl loss in these cells occurs via a cotransport mechanism. In addition, hypotonic media and the other agents used here stimulate a Cl^? -Cl^? exchange, a net loss of K⁺ and a net gain of Na⁺ which are not responsible for cell shrinkage. The Ehrlich cell also appears to have a Ca²⁺-activated, quinine-sensitive K⁺ conductive pathway but this pathway is not part of the mechanism by which these cells regulate their volume following swelling or shrink in isotonic media in response to 2-deoxyglucose or propranolol. Shrinkage by the loss of K⁺ through the Ca²⁺ stimulated pathway appears to be limited by Cl^? conductive movements; for when NO₃^?, an anion demonstrated here to have a higher conductive movement than Cl^?, is substituted for Cl^?, the cells will shrink when the Ca²⁺-stimulated K⁺ pathway is activated.     

Pacemaking mechanism of the afterdischarge of the ovulation hormone-producing caudo-dorsal cells in the gastropod mollusc Lymnaea stagnalis

The ovulation hormone-producing caudo-dorsal cells (CDC) of Lymnaea stagnalis have three states of excitability (active, inhibited, and resting), which are related to the egg-laying cycle. Active state CDC produce a firing pattern of prolonged spiking activity (1 spike/2 s), which in the animal occurs shortly before egg laying. In preparations it is evoked as an afterdischarge upon repetitive stimulation of CDC. The afterdischarge is not synaptically driven, but rests on a pacemaking mechanism. CDC are silent in the inhibited and resting states, which follow egg laying. In these states the membrane potential is mainly dependent on [K⁺]₀. In the active state the ratio of the K⁺, Na⁺, and Ca²⁺ permeabilities has changed considerably, probably resulting from an increased permeability to Na⁺ and Ca²⁺. The firing rate in the afterdischarge is dependent on the membrane potential, which is confirmed experimentally by varying [K⁺]₀.[Na⁺]₀ and [Ca²⁺]₀ directly influence the firing rate. Firing stops in Na⁺-free saline, but is enhanced by Ca²⁺-free or high-Mg²⁺ saline. TTX does not affect firing. Relatively high concentrations of Co²⁺ and La³⁺ (2 × 10^?3M) strongly inhibit CDC. Regular firing can be changed into bursting by various means, such as high K⁺ or addition of 1 mM Ba²⁺. Bursting normally occurs at the beginning of the afterdischarge. Postburst hyperpolarizations are reduced in Ca²⁺-free saline and by low Co²⁺ (10^?4-5 10^?4M). Active CDC are driven by a pacemaking mechanism constituted by a voltage-dependent Na⁺/Ca²⁺ channel and a Ca²⁺-dependent K⁺ channel, thus resembling that of bursting pacemakers. The pacemaking mechanism is inactive in the resting and inhibited state.     

Mathematical model of action potential in higher plants with account for the involvement of vacuole in the electrical signal generation

Electrical signals, including action potential (AP), play an important role in plant adaptation to the changing environmental conditions. Experimental and theoretical investigations of the mechanisms of AP generation are required to understand the relationships between environmental factors and electrical activity of plants. In this work we have elaborated a mathematical model of AP generation, which takes into account the participation of vacuole in the generation of electrical response. The model describes the transporters of the plasma membrane (Ca²⁺, Cl^–, and K⁺ channels, H⁺- and Ca²⁺-ATPases, H⁺/K⁺ antiporter, and 2H⁺/Cl^– symporter) and the tonoplast (Ca²⁺, Cl^–, and K⁺ channels; H⁺- and Ca²⁺-ATPases; H⁺/K⁺, 2H⁺/Cl^–, and 3H⁺/Ca²⁺ antiporters), with due consideration of their regulation by second messengers (Ca²⁺ and IP3). The apoplastic, cytoplasmic and vacuolar buffers are also described. The properties of the simulated AP are in good agreement with experimental data. The AP model describes the attenuation of electrical signal with an increase in the vacuole area and volume; this effect is related to a decrease in the Ca²⁺ spike magnitude. The electrical signal was weakly influenced by the K⁺ and Cl^– content in the vacuole. It was also shown that the contribution of vacuolar IP₃-dependent Ca²⁺ channels into the generation of calcium spike during AP was insignificant with the given parameters of the model. The results provide theoretical evidence for the significance of the vacuolar area and volume in plant cell excitability.     

Conversion of phosphatidylinositol (PI) to PI4‐phosphate (PI4P) and then to PI(4,5)P2 is essential for the cytosolic Ca2+ concentration under heat stress in Ganoderma lucidum

How cells drive the phospholipid signal response to heat stress (HS) to maintain cellular homeostasis is a fundamental issue in biology, but the regulatory mechanism of this fundamental process is unclear. Previous quantitative analyses of lipids showed that phosphatidylinositol (PI) accumulates after HS in Ganoderma lucidum, implying the inositol phospholipid signal may be associated with HS signal transduction. Here, we found that the PI‐4‐kinase and PI‐4‐phosphate‐5‐kinase activities are activated and that their lipid products PI‐4‐phosphate and PI‐4,5‐bisphosphate are increased under HS. Further experimental results showed that the cytosolic Ca²⁺ ([Ca²⁺]_c) and ganoderic acid (GA) contents induced by HS were decreased when cells were pretreated with Li⁺, an inhibitor of inositol monophosphatase, and this decrease could be rescued by PI and PI‐4‐phosphate. Furthermore, inhibition of PI‐4‐kinases resulted in a decrease in the Ca²⁺ and GA contents under HS that could be rescued by PI‐4‐phosphate but not PI. However, the decrease in the Ca²⁺ and GA contents by silencing of PI‐4‐phosphate‐5‐kinase could not be rescued by PI‐4‐phosphate. Taken together, our study reveals the essential role of the step converting PI to PI‐4‐phosphate and then to PI‐4,5‐bisphosphate in [Ca²⁺]_c signalling and GA biosynthesis under HS.     

Lyotropic effects of simple anions on the conformation and interactions of kappa-carrageenan

The effect of different co-anions on the formation and aggregation of the ordered structure of the anionic polysaccharide kappa-carrageenan has been investigated by optical rotation, differential scanning calorimetry, and halide-n.m.r. spectroscopy. The mid-point temperature (T_m) of the disorder—order transition increases systematically with the Hofmeister number for the anion through the lyotropic series SO₄^2? < F^? < Cl^? < Br^? < NO₃^? < I^? < SCN^? when salt concentration and cation (Me₄N⁺ or K⁺) are held constant. A corresponding increase is observed in transition enthalpy (ΔH_cal) and entropy (ΔS_cal). Helix—helix aggregation (as indicated by turbidity, gel formation, and hysteresis between heating and cooling scans) also shows a systematic dependence on the Hofmeister number for the anion, but in the opposite sense. Thus, with tetramethylammonium as the sole counterion present, clear solutions with no thermal hysteresis in the order—disorder transition are observed at all temperatures with I^?, Br^?, NO₃^?, or Cl^? as co-anion, whereas weak, turbid gels with significant thermal hysteresis between melting and setting are formed in the presence of SO₄^2?, and to a lesser degree F^?. With K⁺ as counterion, a similar regular progression is observed through the anion lyotropic series from rapid formation of very turbid gels in the presence of F^?, to very slow development of clear gels with I^? or SCN^?. In agreement with previous studies, an increase in ¹²⁷I-n.m.r. linewidth was observed on conformational ordering of kappa-carrageenan (Me₄N⁺ salt form) in the presence of Me₄NI. However, closely similar behaviour was observed for ³⁵Cl and ⁸¹Br, indicating a simple charge-cloud interaction rather than the specific site-binding of I^? which has previously been suggested.     

Nutrient hot spots in some sierra Nevada forest soils

Re-examination of data distributions from several forested sites in the eastern Sierra Nevada Mountains shows consistent, positive outliers and skew for NH₄ ⁺, NO₃ ^?, and mineral N in resin lysimeters and resin capsules, indicating that most values were low but hotspots of high N flux were present in most cases. Exact causes of these N flux hotspots is not known, but could include water flux hotspots (e.g., preferential flowpaths), microbial hotspots, and possibly the entry of N-enriched O horizon interflow. Soil and resin stake (PRS probe) data from one site (North Lake Tahoe) also showed consistent, positive outliers and skew for NH₄ ⁺, NO₃ ^? , and mineral N, suggesting the presence of microbially produced hotspots. Bicarbonate-P data from soils and ortho-P data from PRS probes also showed highly positive skew and extreme outliers, but Bray (HCl/NH₄F-extractable) P in soils did not. Other measured nutrients (extractable Mg²⁺, K⁺, SO₄ ^2?, and Ca²⁺) also showed positive skew and outliers, but less so than NH₄ ⁺, NO₃ ^?, and mineral N. Calcium stood out among measured nutrients as the most abundant nutrient with the least outliers and the lowest (sometimes negative) skew. The differences in distributions of NH₄ ⁺, NO₃ ^?, and mineral N and those of Ca²⁺ may reflect relative abundance: the most abundant ion, Ca²⁺, shows little evidence of hotspots whereas the much less abundant ions, NH₄ ⁺, NO₃ ^? consistently show evidence of hotspots. We hypothesize that the differing distributions of N and Ca reflect the relative biological competition for these nutrients and that positively-skewed distributions and hotspots will be characteristic of any other nutrient when it is in limited supply relative to biological demand.     

Effects of monovalent cations and anions on ADP-induced aggregation of bovine platelets, and mechanism thereof

The effects of monovalent cations - inorganic alakali metal cations and organic quanternary ammonium cations - and monovalent inorganic anions on ADP-induced aggregation of bovine platelets were investigated. In the presence of K⁺, Rb⁺, Cs⁺, choline or tetramethylammonium, aggeregation proceeded. However, aggregation was markedly restricted in media containing Li⁺, Na⁺, tetrabutylammonium or dimethyldibenzylammonium. With anions, aggregation proceeded in the order Cl⁻ > Br⁻ > I⁻ > Clo₄⁻ > SCN⁻. The effects of cations significantly depended on Ca²⁺ concentration, whereas those of the anions depended little of Ca²⁺. Anions such as SCN⁻ and ClO₄⁻ markedly decreased the fluorescence of the surface charge probe 2-p-tuluidinylnaphthalene-6-sulfonate, whereas cations had less pronouced effects. The relative effects of the anions on the fluorescence were consistent with their relative inhibitory effects on aggregation. These results suggest that inhibition of platelet aggregation by the anions is due to a change in the surface change of the platelet plasma membrane. On the other hand, kinetic analysis suggests that the effects of monovalent cations on platelet aggregation are due to their competition with Ca²⁺ during the process of aggregation.