Gastrointestinal transport of Ca<Superscript>2+</Superscript> and Mg<Superscript>2+</Superscript> during the digestion of a single meal in the freshwater rainbow trout

A diet containing an inert marker (ballotini beads, quantified by X-radiography) was used to quantify the transport of two essential minerals, Ca²⁺ and Mg²⁺ from the diet during the digestion and absorption of a single meal of commercial trout food (3% ration). Initially, net uptake of Ca²⁺ was observed in the stomach followed by subsequent Ca²⁺ fluxes along the intestine which were variable, but for the most part secretory. This indicated a net secretion of Ca²⁺ along the intestinal tract resulting in a net assimilation of dietary Ca²⁺ of 28%. Similar handling of Ca²⁺ and Mg²⁺ was observed along the gastrointestinal tract (GI), although net assimilation differed substantially between the cations, with Mg²⁺ assimilation being close to 60%, mostly a result of greater uptake by the stomach. The stomach displayed the highest net uptake rates for both cations (1.5 and 1.3 mmol kg⁻¹ fish body mass for Ca²⁺ and Mg²⁺, respectively), occurring within 2 h following ingestion of the meal. Substantial secretions of both Ca²⁺ and Mg²⁺ were observed in the anterior intestine, which were attributed to bile and other intestinal secretions, while fluxes in the mid and posterior intestine were small and variable. The overall patterns of Ca²⁺ and Mg²⁺ handling in the GI tract were similar to those observed for Na⁺ and K⁺ (but not Cl⁻) in a previous study. Overall, these results emphasize the importance of dietary electrolytes in ionoregulatory homeostasis.     

Branchial and renal ion fluxes and transepithelial electrical potential differences in rainbow trout,Oncorhynchus mykiss: effects of aluminium at low pH

Synopsis Adult rainbow trout, Oncorhynchus mykiss, were acutely exposed for 4 hours to low pH (4.4) and elevated Al-concentrations (300 µgI^–1) in soft water (Ca²⁺ + Mg²⁺ = 25 µmolI^–1). Comparison of branchial and renal ion fluxes (Na⁺, Cl^–, Mg²⁺, Ca²⁺ and NH₄ ⁺) gave evidence that pH and Al effects were primarily localized at the gill site. The negative whole body ion balance seemed to be caused by stimulatory effects on Na and Cl efflux especially under Al stress and to a lesser extent by inhibition of influx. Measurements of gill potentials indicated positive shifts, which were similar in response to increasing levels of H⁺ ions and Al. It is suggested that Al-induced changes of branchial potentials causes high diffusable loss of ions through interference with membrane-bound Ca²⁺ at the gill site.     

Assessment of ability of endangered Caspian brown trout, <Emphasis Type="Italic">Salmo trutta caspius</Emphasis> (Salmonidae) in production of semen with desirable quality

To assay the effects of stripping frequency on semen characteristics of Caspian brown trout, Salmo trutta caspius, the chemical composition of seminal fluid, sperm production (semen volume, sperm density, spermatocrit,) and sperm motility characteristics (percentage and duration of motility) were investigated over four times stripping during the spawning season. According to data, semen volume, sperm density, osmolality and the concentrations of Na⁺, Cl⁻, K⁺, Ca²⁺, Mg²⁺ and total protein gradually decreased by increasing of stripping frequency. The values of glucose and triglyceride had no significant changes over four times stripping. Also, the values of semen pH, the percentage (5 s after activation) and duration of motility were statistically stable until third stripping but a decrease was recorded for these parameters in the fourth stripping. As well as, significant positive correlations were found for sperm density vs. K⁺, Cl⁻, Na⁺, Ca²⁺, Mg²⁺, total protein, spermatocrit; the percentage of motile spermatozoa vs. Ca²⁺, Mg²⁺, K⁺, Cl⁻, Na⁺, total protein, and also the duration of motility vs. K⁺, Cl⁻, total protein and pH. In text, specific objectives of this study have been expressed.     

Protein digestion and ion concentrations in rainbow trout (Salmo gairdnerii Rich.) digestive tract in sea- and fresh water

• 1.1. Rainbow trout maintained in fresh water or Actapted to sea-water for 24 hr were fed casein-based dry diet. After feeding, fish were kept in fresh water (FW) or transferred to artificial sea-water (SW) and sacrificed after 10 or 20 hr.
• 2.2. The digestive tract was separated into five parts: stomach, pyloric caeca region, middle intestine and two equal lengths of rectum.
• 3.3. The content of these parts was analysed for ions Na⁺, K⁺, Cl⁻, Mg²⁺ and for free, peptide and total amino acids.
• 4.4. In the fish stomach all ions, with the exception of Ca²⁺, indicate drinking of sea-water. In the pyloric caeca region Na⁺ appears to be efficiently absorbed in SW fish but influxed in FW fish. In the rectum of SW fish K⁺ appears to be reabsorbed but Na⁺ concentrated in faeces.
• 5.5. Free amino acid concentrations were always higher in gut lumen of SW than in FW fish in respect to time after feeding and portion of intestinal content. Free amino acids constitute at most 7.4–8.7% of total amino acids in the content of pyloric caeca region.
• 6.6. Peptide amino acids, being mostly di-, tri- and tetra-peptides, increased in stomach content from 14.7 to 28.4% of the total, from 6 to 10 hr after a meal in SW fish. Peptide amino acids constituted 80.3–89.0% of total amino acids in intestinal content of the pyloric caeca region. These peptide portions decreased in the mid-intestine (47.5–52.5%) and increased again in the rectum (73.6–76.0%).
• 7.7. It was concluded that in rainbow trout fed in both sea- or fresh water, ion concentrations do not seem to interfere with protein digestion and nutrient absorption in alimentary tract.

     

Hemolymph ion composition and volume changes in the supralittoral isopod Ligia pallasii Brandt, during molt

We analyzed ion composition and volume of the hemolymph of Ligia pallasii in four different stages of the molt cycle using capillary electrophoresis and ³H-inulin. The main ions in the hemolymph were Na⁺, K⁺, Mg²⁺, Ca²⁺, and Cl⁻. The Ca²⁺concentration increased significantly during the molt by 47% from intermolt to intramolt and by 37% from intermolt to postmolt, probably due to resorption of Ca²⁺ from the cuticle and sternal CaCO₃ deposits. The K⁺ concentration increased significantly by 20% during molt. The hemolymph volume normalized to the dry mass of the animals decreased by 36% from intermolt to late premolt. This was due to a reduction in the hemolymph volume and to an increase in dry mass of the animals during premolt. A sudden increase in the hemolymph volume occurring between late premolt and intramolt served to expand the cuticle. Since the Na⁺, K⁺, Mg²⁺, and Cl⁻ concentrations did not change significantly from late premolt to intramolt, the increase in hemolymph volume suggests an uptake of seawater rather than freshwater. Accepted: 7 March 2000     

The ionic hemolymph composition of the terrestrial isopod Porcellio scaber Latr. during molt

We analyzed the ionic composition of the hemolymph of Porcellio scaber in four different stages of the molt cycle using capillary electrophoresis and calcium selective mini- and microelectrodes. The main ions in the hemolymph were K⁺, Ca²⁺, Na⁺, Mg⁺, and Cl⁻. The values for total calcium obtained by means of capillary electrophoresis and calcium selective minielectrodes did not differ significantly from each other. In situ measurements of the free Ca²⁺ concentration ([Ca²⁺]) by means of calcium-selective microelectrodes indicated that Ca²⁺ is not bound in the hemolymph. During molt the [Ca²⁺] is significantly larger than during intermolt. The [Ca²⁺] increased by 13%, 19% and 18% during premolt, intramolt, and postmolt, respectively. The concentration of the other cations and of Cl⁻ decreased significantly between premolt and intramolt. Thus, the rise of the [Ca²⁺] in the hemolymph is not due to a general increase in all ions, but rather to the resorption of cuticular calcium. Furthermore, the results suggest that K⁺, Na⁺, Mg⁺, and Cl⁻are extruded from the hemolymph during and/or after posterior ecdysis. Accepted: 5 August 1997     

Effects of ionic environment on viscosity of Triton-extracted catch connective tissue of a sea cucumber body wall

Mechanical properties of catch connective tissue are greatly affected by its ionic environment. In order to understand the role of ions, a preparation was developed in which cellular activities were suppressed by treatment with 1% Triton X-100.The material used was body-wall dermis of the sea cucumber Holothuria leucospilota Brandt.The effects of the main cations in seawater (H⁺, Na⁺, K⁺, Ca²⁺, Mg²⁺) on the creep viscosity of the Triton model were compared with those of intact dermis.The comparison distinguished the site of action of ions. K⁺ had its main effect on cells that control the catch mechanism, whereas Ca²⁺ worked directly on extracellular materials. H⁺, Na⁺ and Mg²⁺ had both effects.     

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.     

基于典范对应分析的滨海湿地土壤季节性盐渍化特征

为了更好地开发利用黄河三角洲湿地土壤资源和生态环境建设,运用单因素方差分析(One-way ANOVA)和典范对应分析方法(CCA),对黄河口湿地0—10 cm土壤全盐量(TS)、盐分离子组成、pH、钠吸附比(SAR)、电导率(EC)的季节性变化特征及数量关系进行了分析。结果表明:该区土壤属于盐土类型,春季(5月)、夏季(8月)、秋季(10月)全盐含量均高于17.9 g/kg,且春季、秋季的含盐量高于夏季,造成春、秋季积盐,夏季脱盐。盐分阳离子以Na~+为主,阴离子以Cl~-为主,除Mg~(2+)在夏季、秋季和Cl~-在秋季表现出强烈的变异性外,其余离子在不同季节均表现出中等强度的变异性。春季,Cl~-与Na~+、Mg~(2+),SO■与K~+;夏季,Cl~-与HCO~-_3,SO■与Mg~(2+)、Ca~(2+),Ca~(2+)与Mg~(2+);秋季,Cl~-与SO■,SO■与Mg~(2+),Ca~(2+)与Mg~(2+),均有很好的关联性。pH值均介于7.7—8.1之间,各个季节受盐分离子的影响较小,分布较为均匀。SAR介于3.08—5.29之间,春季受控于HCO~-_3;夏季受控于K~+;秋季受各离子的影响均较小,分布较为均匀。EC介于7.16—13.04 mS/cm,春季受各离子的影响均较小,其空间分布较为均匀;夏季受控于SO■、Ca~(2+)、Mg~(2+);秋季受控于Na~+。TS与Cl~-、Na~+、Mg~(2+)在季节变化上的差异性一致,且各个季节均受控于Cl~-。故通过合理的措施控制或减少Cl~-来源是一条减轻黄河口湿地土壤盐渍化的合适途径。     

Osmoregulation in the brook trout,Salvelinus fontinalis—II. Effects of size,age and photoperiod on seawater survival and ionic regulation

• 1.1. Brook trout (Salvelinus fontinalis) of a single genetic stock, and hatched at the same time, were raised under two photoperiod and two feeding regimes to obtain fish of the same age but with different sizes and photoperiod experiences. In 11 experiments over 1.5 firs, fish were gradually exposed to 32 ppt seawater for 20 days to investigate the ontogeny of salinity tolerance.
• 2.2. Daily changes in plasma osmolarity, [Na⁺], [Cl⁻], [K⁺], [Mg²⁺], thyroxine, hematocrit and gill Na⁺,K⁺-ATPase during adaptation to 10, 20 and 32 ppt were examined in one experiment.
• 3.3. Size was the primary determinant of seawater survival (r² = 0.77) the effect of size on seawater survival slowed after fish reached a fork length of 14 cm. The effect of age on seawater survival (r² = 0.65) was through its covariance with size.
• 4.4. Photoperiod affected seawater survival only through its influence on the timing of male maturation, which decreased salinity tolerance.
• 5.5. Regulation of plasma osmolarity, [Na⁺], [Cl⁻], [K²⁺], [Mg²⁺] and hematocrit in sea water increased linearly with size over the entire range of sizes (6–32 em).
• 6.6. Gill Na⁺,K⁺-ATPase activity after 20 days in seawater decreased with increasing size of brook trout, possibly reflecting decreased demand for active ion transport in larger fish.
• 7.7. Plasma thyroxine concentrations declined in seawater, but no definitive role of this hormone in seawater adaptation was found.
• 8.8. Size dependent survival and osmoregulatory ability of brook trout is compared to other salmonids and a conceptual model is developed.

     

Effects of Seawater Cations and Temperature on Manganese Dioxide-Reductase Activity in a Marine Bacillus

The seawater cations, Na⁺, K⁺, Mg²⁺, and Ca²⁺, each stimulated MnO₂-reductase activity of whole cells and cell extracts of Bacillus 29. Concentrations of Na⁺ and K⁺ which stimulated whole cells and cell extracts maximally were equivalent to those in two- to fivefold diluted seawater. Cell-extract activity was strongly stimulated by Ca²⁺ and Mg²⁺ up to a concentration of 0.01 M Mg²⁺ and 0.002 M Ca²⁺, with little additional stimulation above these concentrations. Whole-cell activity was stimulated biphasically with increasing concentrations of Ca²⁺ and Mg²⁺. Comparison of the effects of individual cations or mixtures of them at concentrations equivalent to their concentration in fivefold diluted seawater showed that more activity was obtained with 0.01 M Mg²⁺ or 0.002 M Ca²⁺ than with 0.1 M Na⁺, and more with 0.1 M Na⁺ than with 0.0022 M K⁺. Fivefold diluted seawater permitted as much or more activity as solutions of individual or synthetic mixtures of the cations. Pre-exposure experiments showed that the ionic history of whole cells was important to their ultimate activity. The MnO₂-reductase activity of induced whole cells exhibited a temperature optimum near 40 C. Cell extracts had different temperature optima (T_opt), depending on whether induced glucose-linked activity (T_opt = 25 C), uninduced glucose-linked, ferricyanide-dependent activity (T_opt = 30 C), or uninduced ferrocyanide-linked activity (T_opt = 40 C) were being measured. Some of these optima are higher than previously reported.     

ROLE OF INORGANIC IONS IN CONTROLLING SEDIMENTATION RATE OF A MARINE CENTRIC DIATOM DITYLUM BRIGHTWELLI1,2

The settling rates and intracellular levels of K⁺, Na⁺, Cl^-, Mg²⁺ and Ca²⁺ were measured in Ditylum bright-welli (West) Grunow, grown axenically in an enriched seawater medium at 20 C at 4,000 lx on an 8:16 LD schedule. Cells at the end of the dark period have high Na⁺ (118 mM), low K⁺ (64 mM) and low Cl^- (117 mM) relative to levels at the end of the light period when K⁺ (126 mM) and Cl^- (154 mM) are high and Na⁺ (101 mM) is low. There is no significant change in Mg²⁺ (16–18 mM) or Ca²⁺ (3–4 mM) with time. The net result of the ion changes during the light period is to increase cell density by about 3.4 mg ml^-1. This change can account for the increase in settling rate of ca. 0.3 day^-1 during the same interval. The density of the cell contents, calculated from observed ion concentrations, is 15–18 mg.ml^-1 less than that of the seawater medium. The ion and settling rate changes are light-dependent and do not persist in the dark or under constant light (ca. 850 lx), but cells do exhibit a free-running circadian rhythm in cell division under continuous dim illumination. The cell vacuole expands during the light period and contracts during the dark, apparently in response to the net ion fluxes. D. brightwelli appears to regulate its density by active ion selectivity accompanied by trans-vacuolar water movement.     

Nonequilibrium Statistical Model of Active Transport of Ions and ATP Production in Mitochondria

A model of the active transport of ions through internal membranes of mitochondria is proposed. If concentrations of ions in a cell are known, this model allows calculating concentrations of all main ions (H⁺, Ca⁺², K⁺, Mg²⁺, Na⁺, Cl⁻) in the mitochondrion matrix and the resting potential across the membrane. The theoretical values satisfactorily agree with available experimental data on the concentrations and the potentials, including different operating regimes of the adenosine triphosphate (ATP) synthetase (the main regime, short circuiting or ATP synthetase blocking). The active transport of Mg²⁺ ions in exchange for protons was assumed. In accordance with the model, the ATP synthetase operation is possible only if the stoichiometric coefficient of protons is 3.     

Inorganic speciation of organotin(IV) cations in natural waters with particular reference to seawater

Abstract

This paper examines the inorganic complexing capacity of seawater, where chloride and sulfate ions are present in high concentration, towards mono- di- and tri-organotin(IV) cations which show a different trend of acidity, depending on cation charges, and a corresponding tendency to hydrolysis. By considering hydrolytic species and chloride and sulphate complex formation, a basic inorganic speciation model of organotins in synthetic seawater (Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl^?, SO₄^2?) has been built up. The model has been extended to also consider interactions of organotins with carbonate and fluoride ions, which are other important components of seawater. Because of the strength of hydrolysis processes, the main complexes formed are in general mixed hydroxo-species. No species are formed by organotin cations and/or their hydroxo-species with fluoride owing to their very low concentration in fluoride, in comparison to the other components of seawater. In order to simplify calculations and to establish a cumulative inorganic binding capacity for seawater, we applied a chemical complexation model, according to which the major inorganic components of seawater are considered as a single salt BA.     

Salicylic Acid Induced Salinity Tolerance Through Manipulation of Ion Distribution Rather than Ion Accumulation

In this research, the effect of different SA concentrations (0, 0.5, 1.0, 1.5, and 2.0 mM) on biological and grain yield as well as Na⁺, K⁺, Cl^?, Ca²⁺, and Mg²⁺ distribution and accumulation in barley plants was examined under nonsaline (2 dS m^?1) and saline (12 dS m^?1) conditions in a three-year field study (2012–2015 growing seasons). Storage factor (SF) was defined as the concentration of an ion in the root, as a proportion of total uptake of that ion, to quantify ion partitioning between root and shoot. Salt stress decreased SF for K⁺, Ca²⁺, and Mg²⁺ and enhanced it for Na⁺ and Cl^?, which led to reduce grain and biological yield. Nonetheless, foliar-applied SA in varying concentrations could lower some of these adverse effects on ion transport and accumulation. At the 2nd and 3rd years, unfavorable climatic conditions such as less precipitation and higher temperature intensified salt stress and decreased the alleviating impact of SA. Foliar application of SA at higher levels increased SF for Na⁺ and Cl^? ions and decreased that for K⁺ indicating that SA helped barley plants keep more Na⁺ and Cl^? and less K⁺ ions in the root system, which suggested the probable role of SA in altering ion transport within the plant in favor of salt stress tolerance. SF was found to be more correlated with grain yield under both nonsaline and saline conditions. Overall, SF might be considered as a potential criterion for salt tolerance in barley plants.     

Evidence that arbuscular mycorrhizal and phosphate-solubilizing fungi alleviate NaCl stress in the halophyte Kosteletzkya virginica: nutrient uptake and ion distribution within root tissues

The effects of an arbuscular mycorrhizal (AM) fungus, Glomus mosseae, and a phosphate-solubilizing microorganism (PSM), Mortierella sp., and their interactions, on nutrient (N, P and K) uptake and the ionic composition of different root tissues of the halophyte Kosteletzkya virginica (L.), cultured with or without NaCl, were evaluated. Plant biomass, AM colonization and PSM populations were also assessed. Salt stress adversely affected plant nutrient acquisition, especially root P and K, resulting in an important reduction in shoot dry biomass. Inoculation of the AM fungus or/and PSM strongly promoted AM colonization, PSM populations, plant dry biomass, root/shoot dry weight ratio and nutrient uptake by K. virginica, regardless of salinity level. Ion accumulation in root tissues was inhibited by salt stress. However, dual inoculation of the AM fungus and PSM significantly enhanced ion (e.g., Na⁺, Cl^?, K⁺, Ca²⁺, Mg²⁺) accumulation in different root tissues, and maintained lower Na⁺/K⁺ and Ca²⁺/Mg²⁺ ratios and a higher Na⁺/Ca²⁺ ratio, compared to non-inoculated plants under 100 mM NaCl conditions. Correlation coefficient analysis demonstrated that plant (shoot or root) dry biomass correlated positively with plant nutrient uptake and ion (e.g., Na⁺, K⁺, Mg²⁺ and Cl^?) concentrations of different root tissues, and correlated negatively with Na⁺/K⁺ ratios in the epidermis and cortex. Simultaneously, root/shoot dry weight ratio correlated positively with Na⁺/Ca²⁺ ratios in most root tissues. These findings suggest that combined AM fungus and PSM inoculation alleviates the deleterious effects of salt on plant growth by enabling greater nutrient (e.g., P, N and K) absorption, higher accumulation of Na⁺, K⁺, Mg²⁺ and Cl^? in different root tissues, and maintenance of lower root Na⁺/K⁺ and higher Na⁺/Ca²⁺ ratios when salinity is within acceptable limits.     

Growth characteristic and ion contents of rice callus under the influence of NaCl and hydroxyproline

Calli of salt tolerant (Bhoora rata) and salt susceptible (GR₁₁) rice varieties were cultured on Linsmaeir and Skoog’s medium containing LD₅₀ concentration of NaCl (200 mM) and hydroxyproline (10 mM). Growth rate of callus and Na⁺, K⁺, Cl⁻, Mg⁺², and Ca⁺² contents of the cultured rice tissues were determined at the end of 0, 2, 4 and 6 weeks of incubation. Hydroxyproline resistant calli of both rice varieties when cultured on Linsmaeir and Skoog’s medium containing both NaCl and hydroxyproline showed increased dry weight and enhanced intracellular levels of K⁺, Mg⁺² and Ca⁺². The accumulation of Na⁺ and Cl⁻ ions was less in the hydroxyproline resistant calli.     

Environmental gradients,plant distribution,and species richness in arctic salt marsh near Prudhoe Bay,Alaska

Spatial patterns of plant cover and species composition in arctic salt marsh and salt affected tundra near Prudhoe Bay, Alaska reflect gradients in elevation, soil conductivity, and soil concentrations of the ions prevalent in seawater. Soil conductivity and soil concentrations of Ca²⁺, Mg²⁺, Na⁺, K⁺, SO₄ ⁼ and Cl^– were significantly related to site elevation, decreasing as elevation increased. Vascular plant species richness increased significantly as soil conductivity and soil ion concentrations decreased, and site elevation increased. Puccinellia phryganodes was the only species present in low elevation sites with low plant cover, high soil conductivity and high soil concentrations of Ca²⁺, Mg²⁺, Na⁺, K⁺, SO₄ ⁼ and Cl^–. Mid-gradient sites were dominated by Carex subspathaceae. Plant cover at these sites was greater than at lower elevation sites, but bare ground was still present. Higher elevation sites had the lowest concentrations of soil ions and the lowest soil conductivities. These sites had little bare ground, contained as many as 16 species, and were dominated by Dupontia fischeri and Eriophorum angustifolium. Ordinations indicated that a complex topographic gradient related most closely to elevation and site distance from the coast best explains variation in the vegetation cover. Irregular deposition along the coastline partially or completely buried three sites in peat or sand up to 20 cm deep. Such rapid changes in plant cover and species composition contributes to the community patch mosaic typical of these marshes. Results suggest an individualistic response of plant species to the environmental gradients in salt marsh and salt affected tundra and are indicative of successional models developed in other marginal arctic environments.     

Role of the choline exchanger in Na-independent Mg efflux from rat erythrocytes

Two types of Na⁺-independent Mg²⁺ efflux exist in erythrocytes: (1) Mg²⁺ efflux in sucrose medium and (2) Mg²⁺ efflux in high Cl⁻ media such as KCl-, LiCl- or choline Cl-medium. The mechanism of Na⁺-independent Mg²⁺ efflux in choline Cl medium was investigated in this study. Non-selective transport by the following transport mechanisms has been excluded: K⁺,Cl⁻- and Na⁺,K⁺,Cl⁻-symport, Na⁺/H⁺-, Na⁺/Mg²⁺-, Na⁺/Ca²⁺- and K⁺(Na⁺)/H⁺ antiport, Ca²⁺-activated K⁺ channel and Mg²⁺ leak flux. We suggest that, in choline Cl medium, Na⁺-independent Mg²⁺ efflux can be performed by non-selective transport via the choline exchanger. This was supported through inhibition of Mg²⁺ efflux by hemicholinum-3 (HC-3), dodecyltrimethylammonium bromide (DoTMA) and cinchona alkaloids, which are inhibitors of the choline exchanger. Increasing concentrations of HC-3 inhibited the efflux of choline and efflux of Mg²⁺ to the same degree. The K_d value for inhibition of [¹⁴C]choline efflux and for inhibition of Mg²⁺ efflux by HC-3 were the same within the experimental error. Inhibition of choline efflux and of Mg²⁺ efflux in choline medium occurred as follows: quinine>cinchonine>HC-3>DoTMA. Mg²⁺ efflux was reduced to the same degree by these inhibitors as was the [¹⁴C]choline efflux.