The Exchangeability of Potassium and Bromide Ions in Cells of Red Beetroot Tissue

The exchangeability of potassium and bromide ions accumulatedby cells of red beetroot tissue has been examined under variousexperimental conditions by means of radioactive tracers. It is established that the cells contain a certain amount ofeasily exchanged ions which is largely independent of the saltcontent of the tissue. The remainder of the salt does not exchangeappreciably within 24 hours either during absorption or whenaccumulation is stopped by low temperature, potassium cyanide,high internal salt content, or by an insufficient preliminarywashing of the material. An hypothesis is proposed that the easily exchanged ions aredistributed throughout the intercellular spaces, cell walls,and in parts of the protoplasm, whilst those which do not readilyexchange may be situated in the cell vacuoles, or else stronglyassociated with protoplasmic constituents. The results suggestthat a considerable barrier to the free diffusion and exchangeof ions is located in the region of the tonoplast of a plantcell, and the metabolic transport of ions across this membraneis discussed. An examination of the changes which occur in the amounts ofreadily exchanged potassium during the washing of freshly cutbeet disks in aerated distilled water indicates that the protoplasmprobably acquires a capacity to fix ions more strongly as aresult of this treatment. This supports the view that an effectof washing on the capacity of cells to absorb salts metabolicallyis to increase the number of ‘absorption centres’involved.     

A Comparison of Washing Methods for Hair Mineral Analysis: Internal Versus External Effects

A major difficulty in hair elemental (mineral) analysis for biomonitoring is adequate understanding of the effectiveness of washing procedures. A review of washing protocols used in hair analysis publications showed little consensus with regard to solvents and surfactants used, washing times, and number of washing stages. Two washing approaches were subsequently used to compare their influence on internal and external surface elemental signals determined with time-of-flight secondary ion mass spectrometry. Na, K, Ca, Mg, and Fe were assessed with regard to their relative signal compared to carbon. Both washing methods had similar effect. All elements except for Fe appear to be removed from the surface of the hair as well as from inside the hair. Only the internal Fe content changed with washing and could indicate that external surface bound Fe may not be removed with most washing procedures. It is shown that washing procedures can have a significant effect on reducing the internal elemental signal levels in hair.     

The cryptonephridial system in the mealworm Tenebrio molitor: Transport of radioactive potassium,thallium and sodium; a functional and structural study

Larvae of the mealworm Tenebrio molitor were injected with radioactive potassium, sodium or thallium solution. It was found that the rectal complex of the animal was labelled with potassium and thallium, but not with sodium. Potassium and thallium labelled the complex to the same level as if the two ions were tracers for each other. Ramsay has found that potassium is actively transported to the complex from the hemocoel and there are reasons to believe that T1+ follows the same pathway. Therefore animals injected with thallium were investigated both by light and electron microscopy. The results suggest that thallium spreads from the hemocoel through the leptophragma to the neighbouring ordinary tubular cells, and in moist mealworms thallium is further found in the perirectal space. Due to diffusion and washing out of thallium during fixation it can not be determined whether T1+ and K+ follow identical pathways, but it is possible to determine how far thallium has penetrated during the experiments.     

Unmasking of a potassium leak in resealed human red blood cell ghosts

A selective potassium leak is observed in resealed, human red blood cell ghosts when hemolysis is performed with distilled water at pH 6.5, 0° C. The leak, which has a maximum near pH 6.7, is suppressed when either magnesium or a chelating agent is present in the hemolysing medium. The potassium leak has the additional property that it can be suppressed after resealing by washing the ghost membranes in a medium containing a low concentration of ATP or EDTA. The data suggest that through the dilution of endogenous chelating agents at hemolysis a potassium leak may be unmasked.     

Unmasking of a potassium leak in resealed human red blood cell ghosts.

A selective potassium leak is observed in resealed, human red blood cell ghosts when hemolysis is performed with distilled water at pH 6.5, 0 degrees C. The leak, which has a maximum near pH 6.7, is suppressed when either magnesium or a chelating agent is present in the hemolysing medium. The potassium leak has the additional property that it can be suppressed after resealing by washing the ghost membranes in a medium containing a low concentration of ATP or EDTA. The data suggest that through the dilution of endogenous chelating agents at hemolysis a potassium leak may be unmasked.     

Key role of external chloride ions in regulation of fast sodium channels in rat cerebellum Purkinje neurons

A decrease in the external chloride ion concentration to 4 mM caused a decrease in the fast sodium current to 85–100% in rat cerebellum Purkinje neurons in the whole-cell configuration using the patchclamp method. This effect did not depend on the main cation from the internal side of the cell membrane (120 mM of potassium or cesium) and also appeared when Cl^– was substituted with sulfate (SO₂^-4) or phosphate (H₂PO₄^-) anion outside of the cell. The effect was reversible after washing out the low chloride by the standard saline.     

Membrane potentials of BHK (baby hamster kidney) cell line: ionic and metabolic determinants

The transmembrane potential of cells from a continuous cell line (BHK-21) has been investigated by a combination of electrophysiological and flame photometric techniques. The ratio of sodium permeability to potassium permeability (P_Na/P_K) determined from membrane potentials recorded at varying external potassium concentrations was 0.082; from membrane potential measurements and the intracellular sodium and potassium concentrations of cells in 6.8 mM K⁺ media the value was 0.075. The P_Na/P_K ratio was not temperature dependent. Dinitrophenol (1 mM) did not significantly alter the membrane potential of cells incubated for one hour with the inhibitor. However, iodoacetate (1 mM) and sodium fluoride (30 mM) caused a significant depolarization during a one-hour incubation. Measurements of sodium and potassium concentrations during incubation at 4°C showed a decrease in internal potassium and an increase in internal sodium accompanied by a decreased membrane potential. Ion concentrations and membrane potentials were measured in cells recovering at 37°C following 24 hours at 4°C. Membrane potentials in excess of E_K during the first ten minutes of recovery may indicate electrogenic pumping.     

Regulation of internal pH of sea urchin sperm. A role for the Na/K pump

In the absence of sodium, sea urchin sperm have an acidic internal pH. The addition of sodium, lithium, or ammonium, but not of potassium ions, induces an internal alkalization. If potassium is added in the presence of sodium, a further alkalization is obtained; in contrast, potassium addition in presence of Li+ or NH+4 does not change the internal pH. The K+-induced pHi change is inhibited by ouabain and when sperm are depleted of their ATP. A large part of the potassium influx is stimulated by Na+, but not Li+, and inhibited by ouabain and cellular ATP depletion. We conclude that activity of Na/K-ATPase pumps located in the plasma membrane of sea urchin sperm could play a role in regulating the internal pH of sea urchin sperm by recycling sodium ions that enter the cell through Na/H countermovements.     

Exodus of 42K+ and 86Rb+ from rat thymic and human blood lymphocytes exposed to phytohemagglutinin.

We have found that PHA produces an alteration in the lymphocyte membrane which allows 86Rb+ or 42K+ in prelabeled lymphocytes to exchange for cations present in washing solutions. These observations suggested that PHA might induce an increase in the exodus of intracellular potassium during incubation in physiologic media. We, therefore, examined 86Rb+ and 42K+ efflux from rat and human lymphocytes during incubation in tissue culture medium. The rate constant for efflux, Ke, was significantly increased by PHA. 86Rb+ efflux was increased by 27% in rat thymic lymphocytes and by 78% in human blood lymphocytes following PHA treatment.     

Impact of improved potassium accumulation on pH homeostasis, membrane potential adjustment and survival of Corynebacterium glutamicum

Metal ion uptake is crucial for all living cells and an essential part of cellular bioenergetic homeostasis. In this study the uptake and the impact of the most abundant internal cation, potassium, were investigated in Actinobacteria, a group of high G+C Gram-positives with a number of prominent biotechnologically and medically important members. Genome analyses revealed a variety of different potassium uptake systems in this monophyletic group ranging from potassium channels common in virtually all Actinobacteria to different active carriers that were present predominantly in pathogenic members able to cope with various stress conditions. By applying Corynebacterium glutamicum as model system we provide experimental evidence that under optimal conditions a potassium channel is sufficient in bacteria for the maintenance of internal pH and membrane potential ensuring survival of cells under stress conditions. Under potassium limitation, however, viability of C. glutamicum was increased under acidic stress or during desiccation when a functional KtrAB potassium transporter from the pathogen Corynebacterium jeikeium was heterologously expressed. We provide experimental evidence that the KtrAB mediated enhanced potassium accumulation improved maintenance of internal pH and membrane potential. The results indicate that the occurrence of active potassium transport systems correlates with an improved potassium-dependent bioenergetic homeostasis and survival of bacterial cells under stress conditions.     

Interaction of internal anions with potassium channels of the squid giant axon

The interaction of internal anions with the delayed rectifier potassium channel was studied in perfused squid axons. Changing the internal potassium salt from K+ glutamate- to KF produced a reversible decline of outward K currents and a marked slowing of the activation of K channels at all voltages. Fluoride ions exert a differential effect upon K channel gating kinetics whereby activation of IK during depolarizing steps is slowed dramatically, but the rate of closing after the step is not much altered. These effects develop with a slow time course (30-60 min) and are specific for K channels over Na channels. Both the amplitude and activation rate of IK were restored within seconds upon return to internal glutamate solutions. The fluoride effect is independent of the external K+ concentration and test membrane potential, and does not recover with repetitive application of depolarizing voltage steps. Of 11 different anions tested, all inorganic species induced similar decreases and slowing of IK, while K currents were maintained during extended perfusion with several organic anions. Anions do not alter the reversal potential or shape of the instantaneous current-voltage relation of open K channels. The effect of prolonged exposure to internal fluoride could be partially reversed by the addition of cationic K channel blocking agents such as TEA+, 4-AP+, and Cs+. The competitive antagonism between inorganic anions and internal cationic K channel blockers suggests that they may interact at a related site(s). These results indicate that inorganic anions modify part of the K channel gating mechanism (activation) at a locus near the inner channel surface.     

Dantrolene suppresses the hyperpolarization or outward current observed during anoxia in hippocampal neurons

Hyperpolarizations, or outward currents, recorded in CA1 pyramidal cells during brief anoxia (2-3 min) (but not postanoxic hyperpolarizations) are markedly reduced (92 +/- 4.8%) by dantrolene sodium, applied by superfusion (10-20 microM). This effect, which is at least partly reversible by prolonged washing, is in keeping with the idea that anoxia activates a Ca2(+)-sensitive K conductance by releasing Ca2+ from internal stores.     

A new spin label method for the measurement of erythrocyte internal microviscosity

A new spin-label method for the measurement of the internal microviscosity of erythrocyte is presented. The spin label used is 2,2',5,5'-tetramethyl-3-maleimidopyrrolidinyl-N-oxyl (MAL-5) which penetrates inside the red blood cell and binds covalently on cytoplasmic glutathione. After washing off the external label, 98% of the electron paramagnetic signal is due to the labelled glutathione. This signal allows one to measure the rotational correlation time of the label. A calibration curve established with spin-labelled glutathione in sucrose solutions of increasing viscosity is used to convert the measured rotation times into viscosity units. This method avoids the use of unphysiological salts like potassium ferricyanide, and permits the study of red blood cells in various suspension media. In normal human subjects, the mean value of microviscosity is 4.45 +/- 0.16 mPa . s at 20 degrees C in isotonic saline (25 subjects) and 6 +/- 0.25 mPa . s in plasma. The variations of microviscosity as a function of the osmolarity of the medium are explained according to a theoretical model taking into account the variations of the red blood cell volume and the viscometric properties of haemoglobin.     

Disappearance of Mating Reactivity in Paramecium caudatum upon Repeated Washing

SYNOPSIS The appearance of mating reactivity of Paramecium caudatum was retarded by repeated washing of the cells in the logarithmic growth phase with Dryl's and other solutions. Highly reactive cells in the stationary phase also lost reactivity during the same treatment. Dryl's solution, sodium and potassium phosphate buffers, Miyake's physiologic balanced solution and exhausted culture medium were effective but deionized water saturated with CaCO₃ was ineffective. The addition of supernatant fluid from stationary phase cultures restored reactivity in 2 hr but was unable to do so when applied to extremely starved cells. These findings may be useful for study of the synthesis of mating-type substances.     

Regulation of ooplasmic sodium and potassium activities in developing locust eggs

Ooplasmic activities of potassium and sodium were measured with ion sensitive microelectrodes before and during the period of maximal water uptake which occurs 3–5 days after oviposition for eggs incubated at 37°C. Potassium activity increased from 84 mM in eggs before fertilization at 118 mM in eggs 1 day after fertilization (d1). Sodium activity increased from 8 mM to 29 mM over the same period. These changes exceeded those predicted from the decrease in water content (8%) during the first day after oviposition. Between d1 and d3, potassium and sodium activities decreased to values predicted on the basis of the 88% increase in egg water content. Although water content increased an additional 46% between d3 and d5, ooplasmic sodium activity remained constant at 11 mM and potassium activity increased from 64 mM to 74 mM during this time. Declines in concentrations of sodium and potassium measured in whole eggs by atomic absorption spectrometry mirrored the increase in egg water content. The results suggest that regulation of ooplasmic sodium and potassium activities is accomplished by release of these ions from internal stores, possibly the york spheres. © 1992 Wiley-Liss, Inc.     

Long duration responses in squid giant axons injected with 134cesium sulfate solutions

Giant axons from the squid were injected with 1.5 M cesium sulfate solutions containing the radioactive isotopes 42K and 134Cs. These axons, when stimulated, gave characteristic long duration action potentials lasting between 5 and 45 msec. The effluxes of 42K and 134Cs were measured both under resting conditions and during periods of repetitive stimulation. During the lengthened responses there were considerable increases in potassium efflux but only small increases in cesium efflux. The selectivity of the delayed rectification process was about 9 times greater for potassium ions than for cesium ions. The data suggest that internal cesium ions inhibit the outward potassium movement occurring during an action potential. The extra potassium effluxes taking place during excitation appear to be reduced in the presence of cesium ions to values between 7 and 22% of those expected in the absence of cesium inhibition.     

Effects of ouabain and osmolarity on bumetanide-sensitive potassium transport in simian virus-transformed 3T3 cells

Unidirectional potassium influx in simian virus-transformed 3T3 cells was dissected into a ouabain-inhibitable "pump' component, a bumetanide-sensitive and chloride-dependent "cotransport' component, and a residual "leak' flux. The bumetanide-sensitive component was stimulated 2-3-fold by a 60-min preincubation with ouabain. Subsequent washing of the cells and incubation in ouabain-free saline reversed both the inhibition of the Na+ pump and the stimulation of bumetanide-sensitive flux. Bumetanide-sensitive potassium influx was also stimulated by hypertonic cell shrinkage (induced by 0.1 M or 0.2 M sorbitol). This latter observation suggests that the bumetanide-sensitive system may play a role in cellular volume regulation.     

Effects of KC 3791 on sodium and potassium channels in frog node of Ranvier

Effects of a new antiarrhytmic compound KC 3791 on sodium (INa) and potassium (IK) currents were studied in frog myelinated nerve fibres under voltage clamp conditions. When applied externally to the node of Ranvier, KC 3791 (KC) at concentrations of 10(-5)-10(-4) mol.l-1 produced both tonic and cumulative (use-dependent) inhibition of INa. An analysis of the frequency-, voltage- and time dependence of cumulative block by KC suggested that this block resulted from a voltage-dependent interaction of the drug with open Na channels. The progressive decrease in INa during repetitive pulsing was due to accumulation of Na channels in the resting-blocked state: closing of the activation gate after the end of each depolarizing pulse stabilized the KC-"receptor" complex. To unblock these channels a prolonged washing of the node had to be combined with a subsequent repetitive stimulation of the membrane; this suggested that channel could not become cleared of the blocker unless the activation gate has opened. KC also proved to be capable of blocking open K channels at outwardly directed potassium currents (IK). This block increased during membrane depolarization. Unblocking of K channels after the end of a depolarizing pulse proceeded much faster than unblocking of Na channels under identical conditions. Cumulative inhibition of outward IK during high-frequency membrane stimulation was therefore readily reversible upon a decrease in pulsing frequency.     

A method for measuring the internal pH in illuminated chloroplasts based on the stimulation of proton uptake by amines.

A simple method for measuring the internal pH of chloroplasts during steady-state illuminations based on the stimulation of proton uptake by monofunctional amines was developed. Predictions of a mathematical derivation concerning the dependence of the stimulation on the amine concentration, the internal volume, the pK of the amine and the external pH have been verified experimentally. To circumvent uncoupling and swelling due to large internal accumulation of amines extrapolation of the stimulation to low amine concentrations was suggested and shown to lead to valid values. Alternatively, swelling could be largely reduced in a medium containing potassium aspartate and valinomycin.     

Thirst and renal excretion of water and electrolytes during pyrogen fever in dogs.

Body temperature, water intake, urine output, sodium and potassium excretion, osmolal and free water clearance, plasma osmolality, sodium and potassium concentrations and osmotic thirst were examined in conscious dogs during pyrogen fever and compared to those found under control conditions. Arterial blood pressure and central venous pressure were also measured in some experiments. Administration of pyrogen produced transient but significant decreases in urine output and striking increases in the spontaneous water intake in some of the experiments in the phase of increasing fever. Arterial blood pressure decreased, whetreas central venous pressure increased at this stage of fever. No significant changes in renal excretion of solutes and free water as well as sodium and potassium were found. Plasma osmolality and sodium concentration increased and potassium concentration decreased unsignificantly both in control and pyrogen experiments. The main finding was that the thirst threshold to osmotic stimuli increased markedly during the phase of stabilized fever may be caused by significant increase in internal body temperature.