Changes in radiocaesium uptake and distribution in wheat during plant development: a solution culture study

Spring wheat plants were grown in a ¹³⁷Cs labelled nutrient solution, either in the presence or absence of NH₄ as a secondary N source. Between 11 and 64 days after sowing (DAS), plants were harvested on nine occasions. The plants supplied with NH₄ and NO₃ had lower root ¹³⁷Cs Activity Concentrations (AC) than those supplied with NO₃ only. Shoot AC were equal in both nutrition treatments. Shoot and root ¹³⁷Cs AC (dry weight basis) showed the same trends with plant age in both nutrition treatments. Shoot AC almost doubled between 11 and 28 DAS after which they gradually decreased concomitant with a similar decrease in K concentrations. Root AC were always higher than shoot AC and increased to a maximum at 35 DAS after which they fluctuated. Expressed on a tissue water basis, the ¹³⁷Cs AC varied less during plant age than did dry weight based AC. Furthermore, root and shoot AC expressed on a tissue water basis were almost equal. It is shown that the initial increase in ¹³⁷Cs AC in both root and shoot can largely be explained by the initial dilution of absorbed ¹³⁷Cs in the unlabelled seedling tissues. No correlation was found between K and ¹³⁷Cs distribution among ears, leaves, stems and roots in 64 old wheat plants. NH₄ as a secondary N source in a nitrate nutrient solution marginally affected ¹³⁷Cs distribution.Abbreviations AC activity concentrations - DAS days after sowing FAX no corresponding author: +3216321997     

Analysis of the genotypic variation in radiocaesium uptake from soil

Young spinach (Spinacia oleracea L., cv. Subito) and wheat (Triticum aestivum, cv. Tonic) plants were hydroponically grown in eight different nutrient solutions containing ¹³⁷Cs. Ca, Mg, K and NH₄ concentrations were varied whilst anion concentrations were equal in all solutions. The large differences in potassium content between spinach and wheat were not reflected in similar differences in ¹³⁷Cs content at any nutritive treatment.Both crops were also grown in a potted podzolic soil contaminated with radiocaesium. This experiment was conducted in a phytotron at two climatic conditions (summer and winter) which differed in day length and light intensity. Wheat plants had higher ¹³⁷Cs levels than spinach at both conditions. The ¹³⁷Cs levels furthermore decreased during development. The ¹³⁷Cs plant/soil solution concentration ratio was lower at the summer than at the winter conditions.     

Distribution and tissue retention of cesium-134 and cobalt-6o in the nile catfish clarias lazera (cuv. & val.)

The Nile catfish, Clarias lazera was found to concentrate radioactive cesium-134 and cobalt-6o from the aquatic environment. For cesium-134 the rate of uptake increased by increase of exposure time, while for cobalt-6o maximum uptake occurred after one day of exposure. The corresponding concentration factors at maximum uptake levels were 0.37 and 0.36 for cesium and cobalt respectively.The internal distribution of these radionuclides in the different tissues and organs of the fish due to uptake from the aquatic environment followed the decreasing order:For ¹³⁴Cs: muscle, bone, gills, stomach, kidneys, intestine and liver.For ⁶⁰Co: bone, muscle, gills, intestine, kidneys, stomach and liver.The internal distribution due to ingestion of these radionuclides followed nearly the same order as was found in case of uptake from the aquatic environment.     

Evaluation of the radioactive Cs concentration in brown rice based on the K nutritional status of shoots

The radioactive cesium (^134,137Cs) concentration in brown rice is correlated with that in the straw/husk. The distribution of ^134,137Cs, resembles that of potassium (K), a homologous element of Cs, in the rice plant body. The relative isotopic abundance of ⁴⁰K is 0.0117 %; thus, 1 g K contains 30.4 Bq ⁴⁰K, and the mass of 4,000 Bq ⁴⁰K is 0.0154 g, indicating that the K concentration can be calculated from ⁴⁰K concentration. We examined if the radioactive Cs concentration in brown rice can be estimated from ⁴⁰K concentrations in straw, and especially might be predicted from the ⁴⁰K:^134,137Cs ratio in straw. We determined the concentrations of ⁴⁰K and radioactive Cs in straw and brown rice, and found a strong correlated-equation (y = 72.922 x^?0.759; r = 0.907) between the radioactive Cs concentration in brown rice and the ⁴⁰K:^134,137Cs ratio in straw. The estimated-radioactive Cs concentration in brown rice can be as much as double, depending on the K nutritional status changing the ⁴⁰K:^134,137Cs ratio in straw. We herein propose a nutritional diagnosis that radioactive Cs concentrations in brown rice can be predicted from the ⁴⁰K:^134,137Cs ratio in shoots.     

The effects of K+ growth conditions on the accumulation of cesium by the bacterium Thermus sp. TibetanG6

The accumulation of cesium by the bacterium Thermus sp. TibetanG6 was examined under different K⁺ growth conditions. The effects of external pH and Na⁺ on the accumulation of cesium were also studied, and the mechanism involved was discussed. K⁺ regimes played an important role in the accumulation of cesium by the strain TibetanG6. The quantity of cesium accumulated (24 h) was much higher in K⁺-deficient regime than that in K⁺-sufficient regime. The pH and Na⁺ had different effects on the accumulation of cesium in the two K⁺ regimes. IR spectra analyses indicated that the biosorption is a process of homeostasis with cesium initially accumulated on the cell wall.     

Comparison of the accumulation of 137Cs and 90Sr by six spring wheat varieties

The uptake of ¹³⁷Cs and ⁹⁰Sr by six varieties of spring wheat (Triticum aestivum) was compared in field trials on land contaminated by the Chernobyl accident. All the experimental varieties are officially adopted for agricultural use in Belarus and are used in large-scale production. Under identical conditions of nutrition, the productivity of the varieties varied significantly by a factor of 1.3. The extent of ¹³⁷Cs and ⁹⁰Sr accumulation by wheat grain, quantified as the concentration ratio, differed between the varieties by as much as a factor of 1.6, for both radionuclides. There was a significant linear positive correlation between the ⁹⁰Sr activity concentration in grain and straw, and the calcium concentration. The correlation between ¹³⁷Cs and potassium was not significant. The results suggest that certain varieties of spring wheat used in normal agricultural practice accumulate less ¹³⁷Cs and ⁹⁰Sr into grain than others. Some spring wheat varieties accumulated relatively less ¹³⁷Cs, but did not accumulate less ⁹⁰Sr. One variety, Quattro, had a significantly lower uptake of both ⁹⁰Sr (for grain) and ¹³⁷Cs (for both grain and straw) than that of the other varieties tested. The reduction efficiency achieved by the use of these varieties, however, is not as high as that achieved by soil amelioration techniques in the past. Nevertheless, since there are no additional costs or production losses associated with these varieties, their use in the contaminated areas is worth considering as a simple, practical, and effective contribution to reducing the uptake of both ⁹⁰Sr and ¹³⁷Cs and allowing farmers to produce food-grade grain.     

137Cs uptake in spring wheat (Triticum aestivum L.cv. Tonic) at varying K supply

Spring wheat (Triticum aestivum L. cv. Tonic) was grown for 16 days in a sandy loam soil which was contaminated with ¹³⁷Cs. The soil was fertilised with K at three rates (0,1 and 2 mmol K per 950 g dry soil) and with NO₃ ^--N at two rates (0 and 2 mmol per 950 g dry soil) in a factorial design. The ¹³⁷Cs Activity Concentration (AC) in the shoot tissue significantly reduced 8.2-fold (nil N treatment, p<0.001) and 9.3-fold (highest N dose, p<0.001) with increasing K supply. In contrast, the K application increased the ¹³⁷Cs AC in soil solution 1.7 fold (nil N treatment) or had no significant effect (highest N dose). At similar K application, the application of N increased the ¹³⁷Cs AC in the shoot compared to the control. This effect is most probably due to the increased NH₄ ⁺ concentration in soil solution which increased the ¹³⁷Cs AC in soil solution. The soil solution composition (¹³⁷Cs and K concentration) in the rhizosphere was estimated from the average soil solution composition at day 16 and solute transport calculations. The ¹³⁷Cs AC in the shoot tissue was predicted from the estimated soil solution composition in the rhizosphere and the relationship between K concentration and ¹³⁷Cs uptake derived from a nutrient solution experiment. The predictions of ¹³⁷Cs AC's in the shoot are qualitatively correct for the fertiliser effects but underestimate the observations between 1.4 and 9.9 fold.     

Potential for phytoextraction of137 Cs from a contaminated soil

Potential for phytoremediation of a soil contaminated with radiocesium was investigated in three phases: (1) hydroponic screening for plant species capable of accumulating elevated levels of cesium in shoots, (2) investigation of several amendments for their potential to increase the bioavailability of ¹³⁷Cs in the contaminated soil, and (3) bioaccumulation of radiocesium in shoots of plants grown in¹³⁷ Cs-contaminated soil.The bioaccumulation ratio for Cs in shoots of hydroponically grown plants ranged between 38 and 165. From solution, dicot species accumulated 2- to 4-fold more cesium in shoots than grasses. In studies investigating the bioavailability of ¹³⁷Cs in aged contaminated soil, ammonium salts were found to be the most effective desorbing agents, releasing approximately 25% of the¹³⁷ Cs. The extent of ¹³⁷Cs desorption from the soil increased with ammonium concentration up to 0.2 M. In a pot study conducted in a greenhouse, there was significant species-dependent variability in the ability to accumulate ¹³⁷Cs in the shoot from contaminated soil. The ability to accumulate ¹³⁷Cs from the soil increased in the order: reed canarygrass (Phalaris arundinacea) < Indian mustard (Brassica juncea) < tepary bean (Phaseolus acutifolius)< cabbage (B. oleracea var. capitata). It was also found that addition of NH₄NO₃ solution to the soil elicited a two- to twelve-fold increase in ¹³⁷Cs accumulation in the shoot. The greatest amount of ¹³⁷Cs (40 Bq g^-1 dw) was removed in shoots of cabbage grown in contaminated soil amended with 80 mmols NH₄NO₃ kg^-1 soil. Bioaccumulation ratios of 2–3 were obtained with the best performing plant species. These values are significantly greater than those previously reported in the literature (usually <0.1) for plants grown on aged contaminated soil. These results indicate that careful species selection along with amendments that increase the bioavailability of¹³⁷ Cs in the soil could greatly enhance the prospects for the use of plants to remediate ¹³⁷Cs-contaminated soils.     

Trophic position and metabolic rate predict the long-term decay process of radioactive cesium in fish: a meta-analysis

Understanding the long-term behavior of radionuclides in organisms is important for estimating possible associated risks to human beings and ecosystems. As radioactive cesium (¹³⁷Cs) can be accumulated in organisms and has a long physical half-life, it is very important to understand its long-term decay in organisms; however, the underlying mechanisms determining the decay process are little known. We performed a meta-analysis to collect published data on the long-term ¹³⁷Cs decay process in fish species to estimate biological (metabolic rate) and ecological (trophic position, habitat, and diet type) influences on this process. From the linear mixed models, we found that 1) trophic position could predict the day of maximum ¹³⁷Cs activity concentration in fish; and 2) the metabolic rate of the fish species and environmental water temperature could predict ecological half-lives and decay rates for fish species. These findings revealed that ecological and biological traits are important to predict the long-term decay process of ¹³⁷Cs activity concentration in fish.     

Untersuchung der im Vergleich zur Kalium-Anreicherung bevorzugten Anreicherung von Cäsium 137 im Säugetierorganismus

Zusammenfassung Es werden Untersuchungen zur Kalium-, Rubidium- und Cäsium- Anreicherung am perfundierten Meerschweinchenherzen durchgeführt. Unter Verwendung der Radionuklide⁴²K,⁸⁶Rb und¹³⁷Cs werden mit Hilfe einer Meßeinrichtung Alkaliionenflüsse zwischen Perfusionslösung und Herzmuskelzelle bestimmt. Es wird die Mehrdeutigkeit der Versuchsergebnisse diskutiert und einexperimentum crucis vorgeschlagen, das entscheiden soll, ob das Ruhepotential als Diffusionsoder als Grenzflächenpotential angesehen werden muß. Im Hinblick auf die unterschiedliche Kalium- und Cäsium-137-Anreicherung im Säugetierorganismus zeigen die Versuche, daß sich Cäsium gegenüber der Muskelzelle qualitativ wie Kalium verhält und daß Cäsium im Herzmuskel nicht bevorzugt angereichert wird.

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On the preferred accumulation of cesium 137 in mammalian organism in comparison with the accumulation of potassiumI. Accumulation of potassium, rubidium and cesium in the perfused guinea-pig heart

Summary Experiments concerning the accumulation of potassium, rubidium and cesium in the perfused guinea-pig heart were performed. Using the radionuclides⁴²K,⁸⁶Rb,¹³⁷Cs and a scintillation counter, the alkali ion fluxes between the perfusion solution and the heart muscle cells are evaluated. The ambiguity of the results is discussed and anexperimentum crucis is proposed which shall decide wether the resting potential has the character of a diffusion or of a phase-boundary potential. As to the different accumulations of potassium and cesium in mammalian organism, our experiments demonstrate that the transport mechanism into the cell is similar for potassium and cesium and that cesium is not accumulated at a higher degree than potassium in the heart muscle cell.

     

Biodistribution of 137Cs in a mouse model of chronic contamination by ingestion and effects on the hematopoietic system

The aim of this work was to define the possible occurrence of hematological changes during the course of a chronic ingestion of ¹³⁷Cs. A mouse model was used, with ingestion through drinking water with a cesium concentration of 20 kBq l⁻¹. Ingestion started in parent animals before mating, and ¹³⁷Cs intake and its effect on the hematopoietic system was studied in offspring at various ages between birth and 20 weeks. ¹³⁷Cs content was measured in various organs, indicating that ¹³⁷Cs was distributed throughout the organism including lympho-hematopoietic organs, i.e., femurs, spleen and thymus. However, we did not observe any effect on the hematopoietic system, whatever the parameter used. In fact, blood cell counts, mononuclear cell counts and progenitor frequency in bone marrow and spleen, and Flt3-ligand, Erythropoietin, G-CSF and SDF-1 concentration in plasma remained unchanged when compared to control animals. Moreover, phenotypic analysis did not show any change in the proportions of bone marrow cell populations. These results indicate that, although ¹³⁷Cs was found in all organs implicated in the hematopoietic system, this did not induce any changes in bone marrow function.     

Pilot Study of Bioaccumulation and Distribution of Cesium,Potassium, Sodium and Calcium in King Oyster Mushroom (Pleurotus Eryngii) Grown Under Controlled Conditions

This pilot study presents preliminary results on interrelations between alkali and alkaline earth elements during their transfer to mycelium and fruitbodies of saprophytic fungi. The accumulation and distribution of four elements (cesium, potassium, sodium, and calcium) was evaluated in king oyster mushroom (Pleurotus eryngii) cultivated under controlled conditions. Elemental composition of caps, stipes, and the substrate was analyzed by atomic absorption/emission spectroscopy to evaluate discrimination, concentration, and transfer factors. The transfer factors determined for all the investigated elements were different and can be put in the following order: Cs > K > Na > Ca. There has been a higher accumulation of cesium in caps than in stipes. Distribution of cesium in fruitbodies depended on the presence of other ions in the substrate. The addition of Ca²⁺ limited the transport of cesium and potassium from stipes to caps. Sodium and calcium were mainly accumulated in the stipes. In a control experiment, without supplementation with K⁺, Na⁺, and Ca²⁺, ～ 62% of the cesium present in the substrate was extracted by mycelium and transported to the fruitbodies. Possible applications of fruiting saprophytic fungi in bioremediation are discussed.     

Sediment cores from shallow lakes preserve reliable,informative paleoenvironmental archives despite hurricane-force winds

Comparison of sediment cores collected in 1999 and 2013 from shallow Lake Harris, Florida, USA showed that the sediment maintained stratigraphic integrity despite multiple hurricanes passing through the area in 2004. Sediments less than 50 years old displayed small losses of organic matter (OM), total phosphorus (TP) and heat-extractable (HE-P) through time that are unrelated to hurricane impacts. Nevertheless, sediment that accumulated between the two core collection dates contained 4-fold more TP than was lost from the sediment over the 14-year period, indicating that sediments in Lake Harris are a net sink for water-column TP. Persistent, elevated ¹³⁷Cs activity in sediments deposited since the mid-1960s indicates protracted cesium input to the lake from this subtropical watershed. There is also evidence for downward transport of ¹³⁷Cs in the sediment profile between core collection dates. Prolonged export of ¹³⁷Cs from the watershed and downward mobility of the radionuclide in the sediment profile diminish the utility of ¹³⁷Cs as a dating tool in Lake Harris.     

Natural and Chernobyl-caused radioactivity in mushrooms,mosses and soil-samples of defined biotops in SW Bavaria

Summary Different mushrooms, mosses and corresponding soil samples have been collected mainly from two sites in the alpine region of southwestern Bavaria. At the end of the growthseason, September 1986, gamma spectroscopic analysis showed that the moss-, mould, and needle-layer contained considerably more ¹³⁴Cs and ¹³⁷Cs activity per unit fresh weight than eight different species of mushroom. These two isotopes were carried into the biotop mainly as a consequence of the Chernobyl accident. ¹³¹J could not be found any more in the samples ca. 5–6 months after the catastrophe. The activity of the cesium isotopes decreased with increasing soil depth. In the mushrooms the activity was relatively high in Xerocomus badius and surprisingly low in Boletus edulis; samples of the latter and of Cantharellus cibarius collected in September 1985 (before the accident) and kept deep frozen contained almost identical amounts of ¹³⁷Cs as those collected from August to October 1986. Mushrooms contained considerably more of the natural isotope ⁴⁰K than the needlelayers and the soil samples in the neighbourhood. In all mushrooms except Xerocomus badius the activity of ⁴⁰K was generally higher than the ¹³⁷Cs activity. The results indicate that except Xerocomus badius the analyzed mushrooms do not actively take up Cs from the soil, in contrast to K.     

Kinetics and competitive modeling of cesium biosorption onto iron(III) hexacyanoferrate modified pine cone powder

This study looked at incorporation of iron(III) hexacyanoferrate onto chemically treated pine cone via iron(III) surface loading and its application for cesium (Cs) adsorption in the presence of alkali/alkali earth metals. The optimum iron(III) loading concentration was 2.50 mol l⁻¹ at pH 7, while optimum hexacyanoferrate (HCF) loading was achieved at a hexacyanoferrate concentration of 0.26 mol l⁻¹. The best-fitting kinetic model was confirmed using the closeness of the predicted equilibrium capacities to the experimentally determined capacity, three error determination methods, and the comparative plots of predictive and experimental uptake of Cs with time. The adsorption rate constants were reduced by alkali/alkali metal addition and the reduction was higher in the HCF-modified pine. The mechanism of Cs adsorption onto raw pine followed the pseudo-second-order model and involved stripping of the hydration water from the metal ion. The presence of Na⁺ did not alter the adsorption mechanism but Ca²⁺ addition changed the best-fitting model to pseudo-first-order. The diffusion-chemisorption model best fitted Cs adsorption onto HCF-modified pine and involved adsorption of Cs in its hydrated form, which migrated easily through the zeolite-like lattice of hexacyanoferrate. Addition of Na⁺ and Ca²⁺ changed the best-fitting model to a pseudo-first-order model.     

Autoradiographische Untersuchungen über die zelluläre Verteilung von Cäsium-134 in der Skelettmuskulatur von Mäusen

Zusammenfassung Die zelluläre Verteilung von ¹³⁴Cs in der Skelettmuskulatur von Mäusen wurde histoautoradiographisch untersucht. 4–6 Std nach einer intraperitonealen Applikation von ¹³⁴CsCl zeigte sich eine starke Anhäufung der ¹³⁴Cs-Aktivität im Bereich des Sarkolemms. Die Aktivität folgte den Konturen der Muskelzellmembran, ein Befund, der auf eine Adsorption der Cs-Ionen an das Sarkolemm schließen läßt. Innerhalb der Myofibrillen zeigte sich eine an die Querstreifung erinnernde Anordnung der Schwärzungen.

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Autoradiographic studies on the cellular distribution of ¹³⁴cesium in the skeletal muscle of mice

Summary The cellular distribution of ¹³⁴Cs in the skeletal muscle of mice was investigated by histoautoradiography. A relatively high accumulation of ¹³⁴Cs was found at the sarcolemma 4–6 hours after intraperitoneal application of ¹³⁴CsCl. This permits the conclusion that Cs-ions are probably adsorbed by the sarcolemma before they are moved into the muscle cell. Within the cell ¹³⁴Cs seems to be linked with myofibrils at destinct distances similar to those between isotropic and anisotropic bands.

     

Variability of water content and of depth profiles of global fallout 137Cs in grassland soils and the resulting external gamma-dose rates

¹³⁷Cs from global fallout of nuclear weapon testings in the 1950s and 1960s was determined in successive layers (0–30 cm) of eight undisturbed grassland soils in Bavaria, Germany. The maximum activity concentration was found in soil layers between 4 and 15 cm below the surface. Using the vertical distribution of the cesium activity, which varied considerably from site to site, the mean residence half-time of ¹³⁷Cs from global fallout in each soil layer was evaluated with a compartment model. These values ranged from 1.0 to 6.3 years/cm. The mean residence half-time averaged over all soil layers and all sites was 2.7±1.4 years/cm and, thus, about twice the corresponding residence half-time of the Chernobyl-derived ¹³⁷Cs as determined in the same soil layers (also in 1993). The dose rate of the external gamma-radiation due to ¹³⁷Cs from global fallout in the soil determined from the depth distributions varied between 0.34 and 0.57 (mean: 0.45±0.07) nGy/h per kBq/m². The effect of soil water content on the dose rate was studied by considering four states of the soil, from water content zero to complete water saturation of the total pore volume. It was shown that the difference between the dose rates at the permanent wilting point and the field capacity, which both represent the most relevant water contents of soils, was only 10% of the dose rate at the permanent wilting point for all sites. Received: 8 September 1997 / Accepted in revised form: 15 December 1997     

No Significant Contribution of Arbuscular Mycorrhizal Fungi to Transfer of Radiocesium from Soil to Plants

The diffuse pollution by fission and activation products following nuclear accidents and weapons testing is of major public concern. Among the nuclides that pose a serious risk if they enter the human food chain are the cesium isotopes ¹³⁷Cs and ¹³⁴Cs (with half-lives of 30 and 2 years, respectively). The biogeochemical cycling of these isotopes in forest ecosystems is strongly affected by their preferential absorption in a range of ectomycorrhiza-forming basidiomycetes. An even more widely distributed group of symbiotic fungi are the arbuscular mycorrhizal fungi, which colonize most herbaceous plants, including many agricultural crops. These fungi are known to be more efficient than ectomycorrhizas in transporting mineral elements from soil to plants. Their role in the biogeochemical cycling of Cs is poorly known, in spite of the consequences that fungal Cs transport may have for transfer of Cs into the human food chain. This report presents the first data on transport of Cs by these fungi by use of radiotracers and compartmented growth systems where uptake by roots and mycorrhizal hyphae is distinguished. Independent experiments in three laboratories that used different combinations of fungi and host plants all demonstrated that these fungi do not contribute significantly to plant uptake of Cs. The implications of these findings for the bioavailability of radiocesium in different terrestrial ecosystems are discussed.     

Testicular steroidogenesis is not altered by 137 cesium Chernobyl fallout,following in utero or post-natal chronic exposure

The testis is especially sensitive to pollutants, including radionuclides. Following the Chernobyl nuclear power plant accident, several of these radionuclides were emitted and spread in the environment. Subsequently, children presented some disruptions of the endocrine system. To determine whether these disruptions were due to 137 cesium (¹³⁷Cs) exposure, the effects of chronic contamination with low doses of ¹³⁷Cs in utero or from birth on testicular steroidogenesis in rats were studied. Contamination was continued for 9 months. No modification was observed in circulating level of hormones (17β-estradiol, testosterone, follicle-stimulating hormone, luteinizing hormone) following in utero or post-natal contamination. Expression of several genes involved in testicular steroidogenesis was affected (cyp19a1, fxr, sf-1), without modification of protein expression or activity. Our results suggest that growing organisms may be affected at the molecular level by ¹³⁷Cs contamination at this post-accidental dose.     

The effect of external cesium ions on the muscle fibre resting potential in mealworm larva (Tenebrio molitor L.)

The membrane potential of ventral longitudinal muscles of Tenebrio molitor larvae was studied as a function of time and of cesium substituted for all or part of external potassium. The conventional microelectrode technique was applied. The mean value of resting potential was — 47.4 mV in standard physiological saline which did not change significantly with time (90 min). Cesium caused, almost immediately, a significant hyperpolarization of membrane potential the magnitude of which depended on cesium concentration. The presence of external potassium enhanced the effectiveness of cesium action, resulting in more pronounced hyperpolarization. The effect of Cs ions was fully reversible upon washing. These data support the idea that inward potassium current can be activated at resting potential level, at least in some cells, including the muscles studied. It is presumed that this potassium current might have some contribution to the resting membrane potential generation in mealworm larva muscles.Abbreviations [K ⁺]₀ extracellular concentration of K ions - E _m resting membrane potential of a cell when bathed in normal saline - E _K K ⁺ equilibrium potential - MP membrane potential - RP resting potential - SD standard deviation - SEM standard error of the mean