Retranslocation of Rb86, Cs137, and K to new leaf growth in bush beans

Summary Bush bean plants were exposed to either Rb⁸⁶ or Cs¹³⁷ with and without carrier rubidium or cesium for 48 hours in a complete nutrient solution. These solutions were then discarded. The plants were then allowed to grow for 11 additional days in complete nutrient solution except that potassium was omitted. Measurement of Rb⁸⁶, Cs¹³⁷, and potassium in new leaves indicated that Cs¹³⁷ was retranslocated to the new growth much slower than was potassium but that proportionately more Rb⁸⁶ was in new leaves than potassium and these results were independent of the presence or absence of the respective carriers. Considerably more Rb⁸⁶ than Cs¹³⁷ was absorbed by the plants either with or without the carriers.     

The uptake,distribution, and translocation of86Rb in alfalfa plants susceptible and resistant to the bacterial wilt and the effect ofCorynebacterium insidiosum upon these processes

Alfalfa (Medicago sativa; L.) plants susceptible (S) and resistant (R) to the bacterial wilt were fedvia roots with a nutrient solution labelled with⁸⁶Rb⁺, at different times after inoculating them withCorynebacterium insidiosum (McCull.) H. L. Jens. The infection did not influence⁸⁶Rb⁺ uptake per plant in the course of a 14-day-period following inoculation, however it did affect its distribution differentially in the S- and the R-plants.⁸⁶Rb⁺ uptake was significantly decreased due to the infection in the S-plants on the day 49 after the inoculation (a 4-h-exposure to⁸⁶Rb⁺), with the iona also being more slowly translocated to the shoots in diseased S-plants than in diseased R-plants. Likely factors causing these effects and their relationship to alfalfa resistance to the bacterial wilt are discussed.     

Adaptation of potassium metabolism and restoration of mitosis during prolonged treatment of mouse lymphoblasts with ouabain

The effects of ouabain on the growth of murine lymphoblasts in vitro have been studied. Exposure of cells to ouabain (0.1 mM) initially inhibited ⁸⁶Rb⁺ uptake rate, reduced the intracellular potassium concentration, and decreased population growth rates. Continued exposure to the same ouabain concentration resulted in an increase of ⁸⁶Rb⁺ uptake rate, intracellular potassium content and population growth rates to control values (adaptation). When treated cells were resuspended in medium free of ouabain after 12 to 15 hours of ouabain treatment, ⁸⁶Rb⁺ uptake rates and intracellular potassium levels exceeded those of untreated cells. Adaptation was inhibited by cycloheximide (3 μg/ml) and by actinomycin D (0.05 μg/ml). Kinetic analysis of transport suggested that while the total capacity of the Na⁺, K⁺ transport system increased, the affinity for both the cation (⁸⁶Rb⁺) and ouabain decreased.     

Ouabain-sensitive 86Rb(K) influx is linked to transepithelial Na transport in pig kidney cell line

The pig kidney cell line, LLC-PK₁, exhibits rheogenic d-glucose coupled transepithelial Na⁺ transport that is inhibited by phlorizin. By measuring the difference in initial rates of influx of ⁸⁶Rb⁺ with and without coupled Na⁺ transport, we can demonstrate an ⁸⁶Rb⁺ uptake linked to Na⁺ transport. The simultaneous determination of phlorizin-inhibited Na coupled d-[³H]glucose uptake and ⁸⁶Rb⁺ influx allows calculation of an Na⁺/Rb⁺ stoichiometry that is consistent with an electrogenic Na⁺ for Rb⁺ exchange.     

Monovalent-ion carrier effects on transport of Rb86 and Cs137 into bush bean plants

Summary Bush bean plants were exposed to either Rb⁸⁶ or Cs¹³⁷ for 24 hours with different monovalent cations as carriers in single-salt solutions except for the presence of 10⁻⁴ M CaCl₂. Ratio of uptake of the radionuclides at 10⁻³ to 10⁻² M was used as an index of the carrier ability of various cations. Different monovalent cations decreased uptake of Cs¹³⁷ and its transport to shoots unequally when 10⁻² M salts were compared with 10⁻³ M salts. Rubidium and cesium salts decreased Cs¹³⁷ uptake equally but potassium salts were less effective in decreasing uptake when the ratios of the two concentrations were considered. All monovalent cations decreased uptake of Cs¹³⁷ at the 10⁻² M carrier concentration but some did not at 10⁻³ M. Nitrate nitrogen was a big factor in these results. Cesium and rubidium salts were most effective. Potassium appeared to increase Cs¹³⁷ transport to shoots particularly at 10⁻³ M KNO₃. Only cesium, rubidium, and potassium salts decreased uptake of Rb⁸⁶ when 10⁻² M salts were compared with 10⁻³ M. Rubidium and cesium salts decreased uptake essentially equally and potassium salts again were less effective. All nitrate salts tended to increase Rb⁸⁶ transport to shoots more consistently than with Cs¹³⁷. It is concluded that absorption and transport to shoots were not equivalent for potassium, rubidium, and cesium.     

22Na+ and 86Rb+ fluxes in spermatozoa and oocytes of arbacia punctulata

The fluxes of ²²Na⁺ and ⁸⁶Rb⁺ in Arbacia sperm and oocytes were studied in order to determine how these cells carry out cation exchange with the sea environment. The uptake of these ions by serum followed a pattern of early rapid influx (initial 0.5 min) and subsequent efflux (1–3 min) followed by a gradual uptake (after 3 min). Neither the uptake nor the efflux of these cations by Arbacia sperm were affected by ouabain, suggesting that influx and efflux of ²²Na⁺ and ⁸⁶Rb⁺ in Arbacia sperm occur predominantly by passive transport. The ²²Na⁺ uptake by Arbacia oocytes showed a steady increase after an initial rapid uptake. A slight but significant inhibition of ²²Na⁺ uptake was observed with ouabain. However, ⁸⁶Rb⁺ uptake by the oocytes reached an early equilibrium and was not affected by ouabain. The uptake of Rb⁺ by Arbacia oocyte is by passive transport while that of Na⁺ is both by passive and active transport.     

Oxidative stress increases potassium efflux from pancreatic islets by depletion of intracellular calcium stores

Oxidative stress to B-cells is thought to be of relevance in declining B-cell function and in the process of B-cell destruction. In other tissues including heart, brain and liver, oxidative stress has been shown to elevate the intracellular free calcium concentration and to provoke potassium efflux. We studied the effect of oxidative stress on Ca²⁺ and K⁺ (Rb⁺) outflow from pancreatic islets using the thiol oxidants DIP and BuOOH. Both compounds reversibly increased ⁸⁶Rb⁺ efflux in the presence of 3 and 16.7 mmol/l glucose. Stimulation of ⁸⁶Rb⁺ efflux was also evident in the absence of calcium. DIP evoked release of ⁴⁵Ca²⁺ from the pancreatic islets both in the presence or absence of extracellular calcium. Employing inhibitors of the calcium-activated potassium channel (K_Ca) and the high conductance K⁺-channel (BK_Ca), the effect of DIP on ⁸⁶Rb⁺ efflux was slightly diminished. Tolbutamide had no effect on ⁸⁶Rb⁺ efflux in the presence of DIP. On the other hand thapsigargin, a blocker of the Ca²⁺-ATPase of the endoplasmic reticulum, completely suppressed the DIP-mediated ⁸⁶Rb⁺ outflow. The data suggest that thiol oxidant-induced potassium efflux from pancreatic islets is mainly mediated through liberation of intracellular calcium and subsequent stimulation of calcium-activated potassium efflux.     

Rb fluxes in Chinese hamster ovary cells as a function of membrane cholesterol content

Steady-state fluxes of ⁸⁶Rb⁺ (as a tracer for K⁺) were measured in Chinese hamster ovary cells (CHO-K1) and a mutant (CR1) defective in the regulation of cholesterol biosynthesis; the membrane cholesterol content of this mutant was varied by growing it on a range of cholesterol supplements to lipid-free medium (Sinensky, M. (1978) Proc. Natl. Acad. Sci. U.S. 75, 1247–1249).Analogous to previous findings in ascites tumor cells, ⁸⁶Rb⁺ influx in the parent strain was differentiated into a ouabain-inhibitable ‘pump’ flux, furosemide-sensitive, chloride-dependent exchange diffusion, and a residual ‘leak’ flux.On the basis of this flux characterization, ⁸⁶Rb⁺ pump and leak fluxes were measured in the mutant as a function of membrane cholesterol content. Pump and leak fluxes, when expressed per ml cell water, were independent of the cholesterol content of the mutant. Moreover, ⁸⁶Rb⁺ fluxes in the mutant were equal to those in the parent strain. Our data imply that the flux behavior of K⁺ in the steady state is independent of the ordering of membrane lipid acyl chains.     

5-Hydroxytryptamine stimulates Rb efflux from pancreatic β-cells

The effects of 5-hydroxytryptamine and 5-hydroxytryptophan on ⁸⁶Rb⁺ efflux from prelabelled ob/ob-mouse islets were studied to better understand the cellular mechanisms underlying the effects of 5-hydroxytryptamine and 5-hydroxytryptophan on insulin release. 5-Hydroxytryptophan (4 mM) had no effect on ⁸⁶Rb⁺ efflux either at a low (3 mM) or at a high (20 mM) d-glucose concentration, whereas 5-hydroxytryptamine (4 mM) stimulated ⁸⁶Rb⁺ efflux at both glucose concentrations. These results indicate that 5-hydroxytryptamine may reduce glucose-induced insulin release by inhibiting early steps in the β-cell stimulus-secretion coupling.     

Delta-endotoxin-induced leakage of 86Rb+-K+ and H2O from phospholipid vesicles is catalyzed by reconstituted midgut membrane

Brush border membrane from Heliothis virescens catalyzed delta-endotoxin-induced leakage of ⁸⁶Rb⁺-K⁺ and H₂O from phospholipid vesicles. Activated delta-endotoxin [CrylA(c)-55 kDa] from Bacillus thuringiensis kurstaki strain EG2244 producing a single CrylA(c) toxin, when incorporated into phospholipid vesicles, made these vesicles more leaky to ⁸⁶Rb⁺-K⁺ than phospholipid vesicles without toxin. This effect was assayed by following the movement of ⁸⁶Rb⁺ into the vesicles in response to a KCl gradient. When toxin was added to the outside of phospholipid vesicles, ⁸⁶Rb⁺ uptake was impeded. Vesicles prepared with H. virescens brush border membrane catalyzed the association of the toxin with the vesicle, and stimulated KCl gradient-induced ⁸⁶Rb⁺ uptake. Toxin did not catalyze the leakage of ³⁶Cl⁻, suggesting that the toxin created a cation-selective leak. Toxin enhanced the permeability of phospholipid vesicles to H₂O, demonstrated by the enhanced rate of vesicle shrinking under increased osmotic pressure. This was analyzed spectrophotometrically by following the rate of vesicle shrinking in response to a 10 mM KCl gradient. In the presence of concentrated phosphatidylcholine vesicles, toxin spontaneously associated with the vesicles so as to enhance the rate of vesicle shrinking in an osmotic gradient. The rate of vesicle shrinking the presence of KCl and toxin was catalyzed by the presence of brush border reconstituted into the vesicles, reducing the effective toxin concentration 1000-fold.     

A single mechanism for the stimulation of insulin release and 86Rb+ efflux from rat islets by cationic amino acids

The mechanisms by which cationic amino acids influence pancreatic B-cell function have been studied by monitoring simultaneously ⁸⁶Rb⁺ efflux and insulin release from perifused rat islets. The effects of two reference amino acids arginine and lysine were compared with those of closely related substances to define the structural requirements for recognition of these molecules as secretagogues. Arginine accelerated ⁸⁶Rb⁺ efflux and increased insulin release in the absence or in the presence of 7mm-glucose. Its effects on efflux did not require the presence of extracellular Ca²⁺ or Na⁺, but its insulinotropic effects were suppressed in a Ca²⁺-free medium and inhibited in an Na⁺-free medium. Among arginine derivatives, only 2-amino-3-guanidinopropionic acid mimicked its effects on ⁸⁶Rb⁺ efflux and insulin release; citrulline, guanidinoacetic acid, 3-guanidinopropionic acid and guanidine were inactive. Norvaline and valine also increased ⁸⁶Rb⁺ efflux, but their effect required the presence of extracellular Na⁺; they did not stimulate insulin release. Lysine as well as the shorter-chain cationic amino acids ornithine and 2,4-diaminobutyric acid accelerated ⁸⁶Rb⁺ efflux in a Ca²⁺- and Na⁺-independent manner. Their stimulation of insulin release was suppressed by Ca²⁺ omission, but only partially inhibited in an Na⁺-free medium. The uncharged glutamine and norleucine increased the rate of ⁸⁶Rb⁺ efflux in the presence of glucose, only if extracellular Na⁺ was present. Norleucine slightly increased release in a Ca²⁺- and Na⁺-dependent manner. The effects of lysine on efflux and release were not mimicked by other related substances such as 1,5-diaminopentane and 6-aminohexanoic acid. The results suggest that the depolarizing effect of cationic amino acids is due to accumulation of these positively charged molecules in B-cells. This causes acceleration of the efflux of K⁺ (⁸⁶Rb⁺) and activation of the influx of Ca²⁺ (which triggers insulin release). The prerequisite for the stimulation of B-cells by this mechanism appears to be the presence of a positive charge on the side chain of the amino acid, rather than a specific group.     

Ba2+-inhibitable86Rb+ fluxes across membranes of vesicles from toad urinary bladder

Summary ⁸⁶Rb⁺ fluxes have been measured in suspensions of vesicles prepared from the epithelium of toad urinary bladder. A readily measurable barium-sensitive, ouabain-insensitive component has been identified; the concentration of external Ba²⁺ required for half-maximal inhibition was 0.6mm. The effects of externally added cations on⁸⁶Rb⁺ influx and efflux have established that this pathway is conductive, with a selectivity for K⁺, Rb⁺ and Cs⁺ over Na⁺ and Li⁺. the Rb⁺ uptake is inversely dependent on external pH, but not significantly affected by internal Ca²⁺ or external amiloride, quinine, quinidine or lidocaine. It is likely, albeit not yet certain, that the conductive Rb⁺ pathway is incorporated in basolateral vesicles oriented right-side-out. It is also not yet clear whether this pathway comprises the principle basolateral K⁺ channel in vivo, and that its properties have been unchanged during the preparative procedures. Subject to these caveats, the data suggest that the inhibition by quinidine of Na⁺ transport across toad bladder does not arise primarily from membrane depolarization produced by a direct blockage of the basolateral channels. It now seems more likely that the quinidine-induced elevation of intracellular Ca²⁺ activity directly blocks apical Na⁺ entry.     

Regulation of 86Rb influx during accumulation of Rb+ or K+ in yeast

The influx rate of ⁸⁶Rb decreases during accumulation of K⁺ or Rb⁺ into metabolizing yeast cells under anaerobic conditions with glucose as substrate. Possible causes for the decrease in the influx rate are examined. It is ruled out that the decrease in the influx rate is caused by an increased turgor pressure of the cells or to an impairment of their energization. During the accumulation of K⁺ or Rb⁺, no decrease but an increase in the protonmotive force of the cells is found. The concomitant increase in cell pH accounts only in small part for the decrease in the influx rates. Acidification of the cells on adding butyrate to the suspension causes a transient increase in the influx rates, whereas the cellular monovalent cation content is still increased. Consequently, no direct relationship is found between the influx rate and the cellular content of K⁺ and Rb⁺.     

Rapid auxin- and fusicoccin-enhanced Rb+ uptake and malate synthesis in Avena coleoptile sections

The short-term effects of auxin (indole-3-acetic acid) and fusicoccin (FC) on Rb⁺ uptake and malate accumulation in Avena sativa L. coleoptile sections have been investigated. FC stimulates ⁸⁶Rb⁺ uptake within 1 min while auxin-enhanced uptake begins after a 15–20-min lag period. Auxin has little or no effect on ⁸⁶Rb⁺ uptake at external pHs of 6.0 or less, but substantial auxin effects can be observed in the range of pH 6.5 to 7.5. Competition studies indicate that the uptake mechanism is specific for Rb⁺ and K⁺. After 3 h of auxin treatment the total amount of malate in the coleoptile sections is doubled compared to control sections. FC causes a doubling of malate levels within 60 min of treatment. Auxin-induced malate accumulation exhibits a sensitivity to inhibitors and pH which is similar to that observed for the H⁺-extrusion and Rb⁺-uptake responses. Both auxin- and FC-enhanced malate accumulation are stimulated by monovalent cations but this effect is not specific for K⁺.Abbreviations FC fusicoccin - IAA indole-3-acetic acid     

Substrate-dependent cadmium toxicity affecting energy-linked K+/86Rb transport inStaphylococcus aureus

Bacteria accumulate high amounts of potassium in the cytoplasm. For studying transport of K⁺ (with⁸⁶Rb as a marker) in bacteria (Staphylococcus aureus 17810S), the cells were depleted of the internal K⁺ pool by a DNP treatment. Kinetics and energetics of⁸⁶Rb transport was assayed with glucose as an exogenous energy source. It was shown that⁸⁶Rb uptake proceededvia a low affinity K⁺ transport system with an apparent,K _m of 2.3 mmol/L Rb⁺. Studies with the lipophilic cation TPP⁺ (tetraphenylphosphonium), the protonophore CCCP (carbonyl cyanide 3-chlorophenylhydrazone) and inhibitors (HQNO-2-heptyl-4-hydroxyquinoline N-oxide; iodoacetate) indicated that⁸⁶Rb transport was driven by Δψ (membrane potential) generatedvia the respiratory chain. The effect of Cd²⁺ on⁸⁶Rb transport was assayed with two energy donors—glucose andL-lactate. It was found that Cd²⁺ strongly inhibited Δψ-dependent⁸⁶Kb transport energized by cadmium-sensitive glucose oxidation, but was not toxic when cadmium-insensitivel-lactate was used as an energy source. The mechanism of these differential, substrate-dependent effects of Cd²⁺ on⁸⁶Rb transport is discussed.     

Effects of acetylcholine and caerulein on 86Rb+ efflux in the mouse pancreas. Evidence for a sodium-potassium-chloride cotransport system

The effect of acetylcholine and the cholecystokinin-like peptide, caerulein on the fractional efflux of ⁸⁶Rb⁺ from preloaded isolated segments of mouse pancreas were studied. Both secretagogues evoked a marked transient increase in ⁸⁶Rb⁺ efflux. The removal of Ca²⁺ from the superfusing medium and addition of 10^?4 M EGTA, markedly reduced, but did not abolish the responses to either acetylcholine or caerulein. Furosemide ($\text{10}{}^{\mathrm{?5}}\text{?10}{}^{\mathrm{?3}}\text{M}$) or piretanide (10^?4 M) reduced the basal efflux and inhibited the secretagogue-elicited responses. Stimulus-induced ⁸⁶Rb⁺ outflow was abolished when the Cl^? component of the superfusing solution was replaced by either NO₃^?, SO₄^2? or I^? but not in case of replacement by Br^?, When Na⁺ was replaced with either Li⁺ or choline⁺ both acetylcholine and caerulein failed to elicit any detectable increase in ⁸⁶Rb⁺ outflow. However, when Tris⁺ was substituted for Na⁺, acetylcholine caused a moderate increase in ⁸⁶Rb⁺ efflux which was abolished by either furosemide (10^?4 M) or chloride depletion (nitrate substitution). The removal of extracellular K⁺ or pretreatment with 10^?3 M ouabain had little effect on secretagogue-evoked ⁸⁶Rb⁺ efflux. These results indicate the presence of a diuretic-sensitive Na⁺-K⁺-Cl^? cotransport system in the mouse pancreatic acinar cell membrane.     

Specific Binding of Rubidium in Chlorella

Specific binding sites for potassium, which may be components of the carriers for active transport for K in Chlorella, were characterized by their capacity to bind rubidium. A dense suspension was allowed to take up Rb⁸⁶ from a low concentration of Rb⁸⁶ and a high concentration of ions which saturate non-specific sites. The amount bound was derived from the increase in the external concentration of Rb⁸⁶ following addition of excess potassium. The sites were heterogeneous. The average affinity of Rb and various other ions for the sites was determined by plotting the degree of displacement of Rb⁸⁶ against log molar concentration of the individual ions. Interpolation gave the concentration for 50 per cent displacement of Rb, which is inversely related to affinity. The order of affinity was not changed when the cells were frozen, or boiled either in water or in 70 per cent ethanol. The affinity is maximal for ions with a crystalline radius of 1.3 to 1.5 A and a high polarizability, and is not related to the hydrated radius or valency. It is suggested that binding groups in a site are rigidly arranged, the irregular space between them being 2.6 to 3.0 A across, so that affinity is high for ions of this diameter and high polarizability.     

Diurnal Rb+ transport inPhaseolus pulvinus

Transport of Rb⁺ from the roots to the pulvinus and its diurnal movement in the pulvinus were investigated. Rb⁺ was given to the roots as its chloride or nitrate. The results showed that (1) Rb⁺ was transported from the roots to the pulvinus through the hypocotyl, epicotyl and petiole, (2) Rb⁺ was absorbed into the pulvinus in exchange for K⁺, (3) the absorbed Rb⁺ moved diurnally in the same phase as the remaining K⁺. Namely, Rb⁺ moved in the pulvinus diurnally just like K⁺.     

Action Spectra for Guard Cell Rb Uptake and Stomatal Opening in Vivia faba

Abaxial epidermal strips, containing guard cells as the only viable cells, were prepared from leaves of Vicia faba following a period in darkness, and floated, under CO₂-free air, on 2 mm RbCl + 0.1 mm CaCl₂ labeled with ⁸⁶Rb⁺. Under white light (high pressure mercury vapor lamp), stomatal opening in these strips approached its maximum at less than 0.02 calorie per square centimeter per minute. Under light of different wavelengths, 20 nanometers apart, and at a low quantum flux density of 7 × 10¹⁴ quanta per square centimeter per second, Rb⁺ uptake and stomatal opening were activated only in the blue and long ultraviolet regions, with a peak at 420 to 460 nanometers. The action spectrum suggests that the underlying process is not photosynthesis. At higher quantum flux density (38 × 10¹⁴ quanta per square centimeter per second), uptake and opening also responded to red (600-680 nanometers) and somewhat to green light, with a minimum at 540 to 560 nanometers, indicating a possible involvement of the photosynthetic process. This light-induced opening appeared not to be mediated by a lowering of CO₂ concentration, since CO₂-free air was used in all treatments and controls. Stomatal opening paralleled Rb⁺ uptake in all cases. This constitutes further evidence for the potassium transport hypothesis of stomatal movement.     

Anti-immunoglobulin-induced potassium flux in relation to capping and DNA synthesis : An analysis in monoclonal human B lymphoma cell populations

F(ab′)₂ anti-μ, as well as anti-δ and anti-γ heavy chains have been found to induce strong increases in the influx of ⁸⁶Rb⁺ (a potassium analogue) in cell suspensions from a proportion of human lymphomas staining monoclonally for B cells. The specificity of the response corresponded to the surface immunoglobulin (sIg) isotype present on lymphoma cells. Even when carried out under closely analogous conditions, no relationship between capping and ⁸⁶Rb⁺ influx was observed. On the other hand, an association between ⁸⁶Rb⁺ influx and mitogenic response to anti-immunoglobulin (anti-Ig) was observed with concordant results in 19 out of 21 comparisons made. These findings suggest that ⁸⁶Rb⁺ influx, which appears to be associated with mitogenic signals, and capping may arise as independent phenomena even when elicited through the same membrane receptor (sIg).