Potassium Ions are More Effective than Sodium Ions in Salt Induced Peptide Formation

Prebiotic peptide formation under aqueous conditions in the presence of metal ions is one of the plausible triggers of the emergence of life. The salt-induced peptide formation reaction has been suggested as being prebiotically relevant and was examined for the formation of peptides in NaCl solutions. In previous work we have argued that the first protocell could have emerged in KCl solution. Using HPLC-MS/MS analysis, we found that K⁺ is more than an order of magnitude more effective in the L-glutamic acid oligomerization with 1,1'-carbonyldiimidazole in aqueous solutions than the same concentration of Na⁺, which is consistent with the diffusion theory calculations. We anticipate that prebiotic peptides could have formed with K⁺ as the driving force, not Na⁺, as commonly believed.     

Absorption of Potassium and Sodium Ions by Carrot Root Tissue Cultures

The absorption of potassium and sodium ions by cultured explantsof young secondary phloem of carrot has been examined. Muchsmaller differences were observed between slowly growing andrapidly growing tissues than in the work of Steward and Millar(1954). This discrepancy is attributed to the use by Stewardand Millar of media of dissimilar mineral salts compositionto grow the two types of tissue. At first, potassium uptake per unit of fresh weight proceededmore rapidly in the actively proliferating cultures than theslowly growing ones, but these ultimately had the greater capacityfor potassium absorption. The rapidly growing cultures showeda higher selectivity towards potassium vis-à-vis sodiumions than did those growing slowly. The effect was evident throughouta culture period of 5 weeks, but was most marked during theearly stages of growth. Some possible explanations of theseobservations are discussed.     

Extrusion of Sodium Ions by Barley Roots: III. The Effect of High Salinity on Long-distance Sodium Ion Transport

The quantity of sodium transported to the shoots of intact barleyplants was stimulated by 0·5 mM ouabain when the sodiumchloride level of the bathing medium was below 100 mM. At sodiumchloride concentrations of 100 mM or more this ouabain-stimulatedsodium transport was not observed. Equiosmotic mannitol, equimolarpotassium chloride or equivalent calcium chloride solutionsdid-not affect the ouabain-stimulated sodium transport froma basic medium containing 10 mM sodium chloride. It is suggestedthat under the present experimental conditions the increasedsodium uptake by the root cells at sodium chloride concentrationsof 100 mM or more masks the extrusion process.     

The Condensation of DNA by Chromium (III) Ions

Abstract

Cr(III), one of the most potent inorganic carcinogens, induces condensation of DNA into a very compact product at 37°, as shown by electron microscopy. The condensation begins with the appearing of some supercoil structures and complete condensation occurs at relatively low Cr(III) concentrations; for 3 and 30 mM ionic strength they are 4.5 and 45 μM, respectively. Under these conditions, Cr(III) inhibits the interaction between ethidium and DNA as shown by absorption and fluorescence spectra.     

Contrasty Staining And Quantitative Determination Of Mucopolysaccharides On Filter Paper By Means Of Colloidal Iron

The contrast between the Prussian blue color of the mucopolysaccharide spots and paper background was increased by differentiation of the paper strips (dyed in acid colloidal iron solution made up in 60% ethanol) with thioglycolic acid. Thus the trivalent iron bound to the paper background was reduced but that adsorbed by the mucopolysaccharides was precipitated as ferric ammonium thioglycolate. This procedure was found to stain equally well acid (including sulfated) and neutral mucopolysaccharides, even though these varieties exhibited different staining properties by the periodic acid-Schiff and toluidine blue dyeing procedures. Staining of different depolymerization products of hyaluronate was little influenced by their chain lengths. Quantitative determination of the mucopolysaccharide content of the spots was performed by elution of ferrocyanide with hot sodium hydroxide and measuring of the Prussian blue color of the extracts, developed on acidification and addition of FeCl₃.     

Extrusion of Sodium and Hydrogen Ions as the Primary Process in Potassium Ion Accumulation by Streptococcus faecalis

Glycolyzing cells of Streptococcus faecalis accumulate K(+) with concurrent extrusion of equivalent amounts of H(+) and Na(+). An attempt was made to clarify the retionship between the movements of Na(+) and K(+). Sodium was displaced from cells glycolyzing in the presence of ammonia, diethylamine, tris(hydroxymethyl)aminomethane, and other nitrogenous cations; by contrast, K(+) was completely retained. Accumulation of K(+) by heterologous exchange for Na(+) was not inhibited by antibiotics which facilitate diffusion of K(+) across the membrane, but was blocked by proton conductors. The results indicate that extrusion of Na(+) and H(+) from the cells is a primary, energy-linked process which generates an electrical potential (interior negative); K(+) accumulation occurs in response to this potential. Two mutants deficient in K(+) accumulation and retention were examined in terms of this model. One mutant is apparently defective in exchange of K(+) for H(+). In the other mutant, exchange of K(+) for Na(+) is impaired.     

Effects of Intracellular Adenosine-5''-diphosphate and Orthophosphate on the Sensitivity of Sodium Efflux from Squid Axon to External Sodium and Potassium

A study was made of sodium efflux from squid giant axon, and its sensitivity to external K and Na. When sodium efflux from untreated axons was strongly stimulated by K_o, Na_o was inhibitory; when dependence on K_o was low, Na_o had a stimulatory effect. Incipient CN poisoning or apyrase injection, which produces high intracellular levels of ADP¹ and P_i, rendered sodium efflux less dependent on external K and more dependent on external Na. Injection of ADP, AMP, arginine, or creatine + creatine phosphokinase, all of which raise ADP levels without raising P_i levels, had the same effect as incipient CN poisoning. P_i injection had no effect on the K sensitivity of sodium efflux. Axons depleted of arginine and phosphoarginine by injection of arginase still lost their K sensitivity when the ATP:ADP ratio was lowered and regained it partially when the ratio was raised. Rough calculations show that sodium efflux is maximally K_o-dependent when the ATP:ADP ratio is about 10:1, becomes insensitive to K_o when the ratio is about 1:2, and is inhibited by K_o when the ratio is about 1:10. Deoxy-ATP mimicked ADP when injected into intact axons. Excess Mg, as well as P_i, inhibited both strophanthidin-sensitive and strophanthidin-insensitive sodium efflux. An outline is presented for a model which might explain the effects of ADP, P_i and deoxy-ATP.     

Effects of Sodium, Potassium, and Calcium Ions on Slow and Spike Potentials in Single Photoreceptor Cells

The influence of changes in the ionic composition of the bathing medium on responses of the retinula cell of the honeybee drone to light was examined by means of intracellular microelectrodes. The resting potential of the cell was influenced mainly by the concentration of K. The peak of the receptor potential (the transient), which in a normal solution and with strong light approaches zero membrane potential, overshot this level in a K-rich solution. An increase in the concentration of K also raised the level of the steady-state phase of the receptor potential (the plateau). The amplitude of the receptor potential was decreased and the spike potential rapidly abolished when Na was replaced by either sucrose, choline, or Tris. In a Ca-free solution the amplitude of the response and especially that of the plateau, was increased. An increase in Ca had the opposite effects. All these changes were reversible. An attempt was made to interpret the receptor and spike potentials in terms of passive movements of Na and K across the membrane of the retinula cell. The major difficulty encountered was to find an explanation for the persistence of an appreciable fraction of the transient and the plateau in preparations kept up to 12 hr in a solution in which all the Na had been replaced by choline, Tris, or sucrose.     

Homeostasis of Sodium and Potassium Ions in Erythrocytes of the Lamprey Lampetra fluviatilis: Effect of Ion Transport and Metabolic Blockers, and Ionophores

After incubation of lamprey Lampetra fluviatilis erythrocytes in the standard medium for 90–120 min, intracellular Na⁺ and K⁺ content remained unchanged (28.7 ± 1.1 and 66.3 ± 1.5 mmol/l cells, respectively, n = 33). The erythrocyte ion content also did not change after treatment of the cells with ion transport inhibitors, Ba^{2 +} and amiloride. Addition of 0.1 mM ouabain to the incubation medium led to a decrease of K⁺ content by 8.4 ± 1.2 and to an increase of Na⁺ content by 2.4 ± 0.8 mmol/l/2 h. Similar reciprocal changes in the cellular ion composition were observed after treatment of the erythrocytes by oxidative metabolism inhibitors (rotenone and CCCP—carbonyl cyanide m-chlorophenyl-hydrazone). The metabolic blockers produced more significant ion composition changes in comparison with ouabain. An increase of intracellular Na⁺ content under effect of CCCP was completely inhibited by amiloride. It can be suggested that inhibition of oxidative metabolism is accompanied by a cell acidification and Na⁺/H⁺ exchange activation. Erythrocyte acidification by a K⁺/H⁺ ionophore led to a rapid cellular Na⁺ accumulation, which indicates the presence of a Na⁺/H⁺ exchanger with high activity. The K⁺ ionophore valinomycin produced a relatively small K⁺ loss from the lamprey erythrocytes to indicate a low anion conductance of the cells. The data obtained indicate an important role of oxidative metabolism in the monovalent ion homeostasis in the lamprey red blood cells.     

The Dual Effect of Lithium Ions on Sodium Efflux in Skeletal Muscle

Sartorius muscle cells from the frog were stored in a K-free Ringer solution at 3°C until their average sodium contents rose to around 23 mM/kg fiber (about 40 mM/liter fiber water). Such muscles, when placed in Ringer''s solution containing 60 mM LiCl and 50 mM NaCl at 20°C, extruded 9.8 mM/kg of sodium and gained an equivalent quantity of lithium in a 2 hr period. The presence of 10^-5 M strophanthidin in the 60 mM LiCl/50 mM NaCl Ringer solution prevented the net extrusion of sodium from the muscles. Lithium ions were found to enter muscles with a lowered internal sodium concentration at a rate about half that for entry into sodium-enriched muscles. When sodium-enriched muscles labeled with radioactive sodium ions were transferred from Ringer''s solution to a sodium-free lithium-substituted Ringer solution, an increase in the rate of tracer sodium output was observed. When the lithium-substituted Ringer solution contained 10^-5 M strophanthidin, a large decrease in the rate of tracer sodium output was observed upon transferring labeled sodium-enriched muscles from Ringer''s solution to the sodium-free medium. It is concluded that lithium ions have a direct stimulating action on the sodium pump in skeletal muscle cells and that a significantly large external sodium-dependent component of sodium efflux is present in muscles with an elevated sodium content. In the sodium-rich muscles, about 23% of the total sodium efflux was due to strophanthidin-insensitive Na-for-Na interchange, about 67% being due to strophanthidin-sensitive sodium pumping.     

Effect of Sodium Ions on Calcium-Loaded Rat Heart Mitochondria and Frog Myocardium

Journal of Evolutionary Biochemistry and Physiology - The effect of calcium load on rat heart mitochondria [RHM(K+)], in which K+ ions in the matrix were partially replaced by Na+ ions [RHM(Na+)],...     

On the Physiology Of Attention (1)

In the course of organizing teaching practice in the schools for student physiologists of the university, we became convinced that holding the children's attention to the subject of the lesson is one of the most difficult tasks not only for a teacher at the beginning of his career, but for an experienced one.     

A Quantitative Study of the Enhancing Effect of Nickel Ions on the Taste Response to Sodium Ions of Single Fibers of the Frog Glossopharyngeal Nerve: Competitive Inhibition by Calcium Ions of the Nickel-Enhanced Response to Sodium Ions

Single water fibers of the frog glossopharyngeal nerve respondto relatively high concentrations of NaCl (>80 mM). NiCl₂at 1 mM enhanced the Na⁺ response and reduced the thresholdconcentration for NaCl to 20 mM. CaCl₂ at 0.5–1 mM inducedan inhibition of the Ni²⁺-enhanced response to Na⁺ ions. A quantitativeexplanations for these results is provided by the hypothesisthat Ni²⁺ ions secondarily affect a sodium receptor or channel(designated X_Na^*) that is responsible for the Na⁺ response andthat Ca²⁺ ions inhibit the Ni²⁺-enhanced response to Na⁺ ionsby competing with Na⁺ ions for X_Na^*. Double-reciprocal plotsof the experimental data indicate that the affinity of X_Na^*for both Na⁺ ions (agonist) and Ca²⁺ ions (competitive antagonist)in the presence of 1 mM NiCl₂ was five times higher than thepreviously reported values obtained in the absence of NiCl₂(Kitada, 1991). Ni²⁺ ions at 1 mM enhanced the maximal responseto Na⁺ ions by 190%. It appears that a sodium receptor (or channel)interacts with a Ni²⁺-binding element that is affected by Ni²⁺ions and, thus, Ni²⁺ ions can induce both an increase in theaffinity of the sodium receptor for the respective cations andan enhancement of the Na⁺ response. Chem Senses 21: 65–73,1996.     

Accumulation of Iron in the Rabbit Erythroid Cell As Affected by Ouabain, Sodium and Potassium Ions, and Temperature

Reticulocytosis was induced in rabbits with phenylhydrazine. The accumulation of a small part of ⁵⁹Fe in blood cells of these animals was inhibited by ouabain and related to changes in extracellular sodium and potassium concentrations. Sodium increases movement from the cell surface into the cell, whereas potassium and ouabain decrease this movement. ⁵⁹Fe movement was found to be temperature-dependent. Thus, the Na-K ATPase system appears to be important in the movement of iron from the cell membrane (stroma) to the cell interior, but influences only a small part of the total iron transport.     

Effect of chromium(III) on poly(dG-dC) conformation

The interaction of chromium(III) with poly(dG-dC) inhibits the B to Z transition and results in the condensation of the polymer at high Cr/nucleotide ratios. At low Cr/nucleotide ratios chromium(III) enhanced the ability of ethanol to induce the B to Z transition of poly(dG-dC). The effects of chromium(III) on the conformation of DNA may be related to the carcinogenicity of chromium compounds.     

Properties of (Sodium Potassium)-Stimulated ATPases in English Ryegrass Roots and Implications in Ion Transport

Maximum ATPase activities in the cell wall fraction of English ryegrass (Lolium perenne L.) roots were stimulated by foru discrete millimole ratios of (Na⁺+ K⁺); 40:0, 35:5, 5:35, and 0:40. The optimal pH for stimlation was found to be 6.5. Contrary to data in the literature, Mg²⁺ inhibited all stimulatory ratios of (Na⁺+ K⁺) when plants were cultured on an adequate nutrient solution. When grown on a dilute solution, Mg²⁺ enhanced (Na⁺+ K⁺)-stimulated ATPase activity in this membrane preparation. The single optimal combined concentration of (Na⁺+ K⁺) for all stimulatory ratios was 40 MM. The ratios of (Na⁺+ K⁺) which stimulated ATPase activity in the cell wall fraction varied with position along the root axis such that all rarely existed simultaneously nor did any exist in the terminal millimetre of the root. Both cell wall and microsomal fractions showed stimulation by (Na⁺+ K⁺) at all the above ratios indicating the possible presence of plasma membrane fragments in both fractions. Only the 35:5 ratio was stimulations were found in the supernatant. Implications of ion-stimulated ATPase involvement in ion transport were drawn from the appearance of ATPase activity at a 40:0 ratio of (Na⁺+ K⁺) and the disappearance of stimulations at 35:5, 5:35, and 0:40 ratios when plants were moved from a strong (35 mM total concentration) to a dilute (0.75 mM) nutrient solution.