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PubMed2001

Mineralogical and hydrochemical effects on adsorption removal of cesium-137 and strontium-90 by kaolinite.

Adsorption characteristics of the nuclides onto kaolinite were investigated by batch experiment under various pH conditions and concentrations of groundwater cations (Ca2+, Mg2+, K+ and Na+) and anions (HCO3-, CO3(2-) and SO4(2-). Adsorption removal of 137Cs and 90Sr by kaolinite greatly increased as the concentration of groundwater cations increased from 10(-5) to 10(-1) M. In contrast, the pH exerted a small effect on the adsorption of 137Cs and 90Sr onto kaolinite. The zeta potential of kaolinite particles showed a negative increase of amphoteric surface charge with increasing pH. The adsorption behavior of 90Sr was also highly dependent on the concentration of bicarbonate. The thermodynamic saturation index indicated that bicarbonate exerts great effect on strontium adsorption by the precipitation of a strontianite (SrCO3) and a change in pH.

Adsorption↗
PubMed1972

Negative conductance caused by entry of sodium and cesium ions into the potassium channels of squid axons.

Internal Cs(+), Na(+), Li(+), and, to a lesser degree, Rb(+) interfere with outward current through the K pores in voltage clamped squid axons. Addition of 100 mM NaF to the perfusion medium cuts outward current for large depolarizations about in half, and causes negative conductance over a range of membrane voltages. For example, suddenly reducing membrane potential from +100 to +60 mv increases the magnitude of the outward current. Internal Cs(+) and, to a small extent, Li(+), also cause negative conductance. Na(+) ions permeate at least 17 times less well through the K pores than K(+), and Cs(+) does not permeate measurably. The results strongly suggest that K pores have a wide and not very selective inner mouth, which accepts K(+), Na(+), Li(+), Cs(+), tetraethylammonium ion (TEA(+)), and other ions. The diameter of the mouth must be at least 8 A, which is the diameter of a TEA(+) ion. K(+) ions in the mouths probably have full hydration shells. The remainder of the pore is postulated to be 2.6-3.0 A in diameter, large enough for K(+) and Rb(+) but too small for Cs(+) and TEA(+). We postulate that Na(+) ions do not enter the narrower part of the pore because they are too small to fit well in the coordination cages provided by the pore as replacements for the water molecules surrounding an ion.

Animals↗
PubMed1973

Differential responses of crab neuromuscular synapses to cesium ion.

Excitatory postsynaptic potentials (EPSP's) generated in crab muscle fibers by a single motor axon, differ in amplitude and facilitation. Some EPSP's are large at low frequencies of stimulation and show little facilitation; others are smaller and show pronounced facilitation. When K(+) is replaced by Cs(+) in the physiological solution, all EPSP's increase in amplitude, but small EPSP's increase proportionately more than large ones. Quantal content of transmission, determined by external recording at single synaptic regions, undergoes a much larger increase at facilitating synapses. The increase in quantal content of transmission is attributable to prolongation of the nerve terminal action potential in Cs(+). After 1-2 h of Cs(+) treatment, defacilitation of synaptic potentials occurs at synapses which initially showed facilitation. This indicates that Cs(+) treatment drastically increases the fraction of the "immediately available" transmitter store released by each nerve impulse, especially at terminals with facilitating synapses. It is proposed that facilitating synapses normally release less of the "immediately available" store of transmitter than poorly facilitating synapses. Possible reasons for this difference in performance are discussed.

Action Potentials↗
PubMed1976

Potassium current and the effect of cesium on this current during anomalous rectification of the egg cell membrane of a starfish.

The kinetics of the membrane current during the anomalous or inward-going rectification of the K current in the egg cell membrane of the starfish Mediaster aequalis were analyzed by voltage clamp. The rectification has instantaneous and time-dependent components. The time-dependent increase in the K conductance for the negative voltage pulse as well as the decrease in the conductance for the positive pulse follows first-order kinetics. The steady-state conductance increases as the membrane potential becomes more negative and reaches the saturation value at about -40 mV more negative than the K equilibrium potential, V(K). The entire K conductance can be expressed by g(K).n; g g(K) represents the component for the time-independent conductance which depends on V-V(K) and [K+]o, and n is a dimensionless number (1 is greater than or equal to n is greater than or equal to 0) and determined by two rate constants which depend only on V-V(K). Cs+ does not carry any significant current through the K channel but blocks the channel at low concentration in the external medium. The blocking effect increases as the membrane potential is made more negative and the potential-dependent blocking by the external Cs+ also has instantaneous and time-dependent components.

Animals↗
PubMed1981

Cesium blockade of delayed outward currents and electrically induced pacemaker activity in mammalian ventricular myocardium.

The effects of Cs+, 5-25 mM, were studied in cat and guinea pig papillary muscles using voltage clamp and current clamp techniques. In solutions containing normal K+, the major effects of Cs+ were depolarization of the resting potential and reduction of the delayed outward current (ixl) between -80 and -20 mV. Both inward and outward portions of the isochronal current voltage relation (l-s clamps) were reduced by extracellular Cs+. This resulted in a substantial reduction of inward rectification and, by subtraction from the normal I-V relationship, the definition of a Cs+-sensitive component of current. Under current clamp conditions, 5-10 mM Cs+ produced a dose-dependent slowing of repetitive firing induced by depolarization. At higher concentrations (25 mM) the resting potential was depolarized and repetitive activity could not be induced by further depolarization. However, release of hyperpolarizing pulses was followed by prolonged bursts of repetitive action potentials, suggesting partial reversal of blockade or participation of another pacemaker process. The experimental results and a numerical simulation show that under readily attainable conditions, reduction in an outward pacemaker current may slow pacemaker activity.

Action Potentials↗
PubMed1984

Calcium-mediated inactivation of the calcium conductance in cesium-loaded frog heart cells.

Ca current inactivation was investigated in frog atrial muscle under voltage-clamp conditions. To inhibit the outward currents, experiments were performed on Cs-loaded fibers and in 20 mM Cs (K-free) Ringer with 4-AP added. Inactivation, produced by a conditioning pulse, was measured by reducing the current during a subsequent test pulse. The extent of inactivation increased initially with prepulse amplitude and then decreased as the prepulse potential became progressively positive. Relative inactivation follows a U-shaped curve. When Sr was substituted for Ca, both the degree and the rate of inactivation decreased. Relative inactivation appeared to be linearly related to the amount of divalent cations (Ca and Sr) carried into the cell during the prepulse. Elevating Ca enhanced peak current and accelerated its decline. Elevating Mg decreased peak current and slowed its decline. An application of Na-free (LiCl) solution resulted in a somewhat smaller but faster inactivating current. Adrenaline increased and D600 decreased the maximal Ca conductance with little alteration in the inactivation rate; Co decreased both peak current and the rate of inactivation. Enhancement of the outward currents, reduced driving force, and intracellular surface charge screening do not adequately account for the above results. Evidence was considered that Ca entry mediates most of Ca current inactivation in frog atrial fibers. Removal from inactivation was also investigated in normal-Ca, Ca-rich, and Sr solutions. Recovery after partial inactivation by high depolarization was biphasic. Recovery was slowed by 10 Ca and accelerated by 1.8 Sr, whereas opposite effects have been shown on activation.

Animals↗
PubMed1984

Changes in external Na induce a membrane current related to the Na-Ca exchange in cesium-loaded frog heart cells.

The effects of transient alterations in Nao were investigated under voltage clamp conditions in frog heart cells previously loaded with Cs. Tetrodotoxin and Cs were used to inhibit Na and K currents. On applying a Na-poor solution (39.2 mM), an outward current was generated during both depolarizations and hyperpolarizations. The current amplitude described a U-shaped function of the membrane potential. On reapplying the standard solution after 15 min equilibration, an inward current was then induced that exhibited a bell-shaped function of the membrane potential. Current amplitude was sensitive to the external Ca concentration. Increasing pHi by 10 mM NH4Cl enhanced this current, while the internal acidification that occurred on switching back to the control solution greatly reduced it. Variations in the amplitude of this current during repetitive stimulations or long pauses are best explained by subsequent alterations in Nai and pHi; no evidence for a time dependence was found. This current was inhibited by La3+, Co2+, and D600, and was sensitive to adriamycin, quinidine, and disopyramide; lidocaine, another local anesthetic, and nifedipine had no effect. These observations extend previous work on intact heart cells and sarcolemmal vesicles. They suggest that the Na-Ca exchange may generate a current that is outward when Ca ions are moving into the cell.

Amiloride↗
PubMed1988

Efficacy of brachytherapy with californium-252 neutrons versus cesium-137 photons for eradication of bulky localized cervical cancer: single-institution study.

A fast-neutron-emitting radioisotope, 252Cf, is being tested in clinical trials of neutron brachytherapy for cervical cancer. The efficacy for histological eradication of bulky stage IB cervical tumors (mean diameter, approximately 6 cm) using combined radiation and surgery was studied in 65 patients treated with 137Cs or 252Cf before surgery during 1983-1986. Forty-four patients were treated with 137Cs and 21 were treated with 252Cf at equivalent doses of radiation. Fifteen of the 44 specimens (34%) were positive after 137Cs therapy. Only one of the 21 specimens was positive after 252Cf therapy (P = .025), and that patient was treated in a delayed schedule 21 days after the start of external-beam irradiation rather than early in the course. 252Cf therapy required a much lower radiation dose and shorter treatment time. The study compared tumor destruction of an identically staged human cervical tumor in situ by direct histological means, using 252Cf neutron therapy or conventional photon therapy at an identical and equivalent dose adjusted by a relative biological effectiveness of 6.0 for 252Cf.

Adult↗
PubMed1976

Propidium diiodide-cesium chloride density gradient centrifugation for buoyant separations of duplex DNA molecules containing single-stranded regions.

At increasing dye concentrations in propidium diiodide-CsCl density gradients, the relative buoyant density shift was largest for open-circular duplex phiX174 DNA (RFII), next largest for single-stranded viral DNA, and least for closed-circular duplex DNA (RFI). These differential relative buoyant density shifts permitted discrete separations of these phiX DNA forms. Further, in propidium diiodide-CsCl density gradients, the distinctive density of single-stranded DNA permitted separations of rolling-circle intermediates with a single-stranded tail that occur during single-stranded phiX DNA synthesis. It is suggested that single-strandedness in a duplex DNA structure influences its buoyand density shift due to differential dye binding to the single-stranded region and is an additional physical basis for relative buoyant separations of DNA molecules in propidium diiodide-CsCl density gradients.

Centrifugation, Density Gradient↗
PubMed1981

Isolation of a 5S RNA-protein L5 complex from 60S subunits of rat liver ribosomes by cesium sulfate density-gradient equilibrium centrifugation.

Upon CS2SO4 density-gradient equilibrium centrifugation, 60S subunits of rat liver ribosomes were dissociated to form three bands at the densities of 1.55, 1.40, and 1.30 g/ml. The bands at 1.55 and 1.30 g/ml were shown to contain exclusively RNA or proteins, respectively, whereas the band at 1.40 g/ml contained both RNA and a protein. The RNA in the 1.40 g/ml band was identified as 5S RNA and the protein in this band was protein L5. An empirical calculation suggested that the 1.40 g/ml band contained an equimolar 5S RNA-protein L5 ribonucleoprotein complex. This finding may indicate that protein L5 is located in very close proximity to 5S RNA in large ribosomal subunits.

Animals↗
PubMed1994

Cesium prevents maintenance of long-term depression in rat hippocampal CA1 neurons.

Long-term depression of field excitatory postsynaptic potentials (EPSP) in the CA1 region of hippocampal slices was evoked by delivering a 15 min train of pulses at 1 Hz to the Schaffer-commissural-CA1 pathway, and prevented by adding an N-methyl-D-aspartate (NMDA) receptor antagonist (AP-5, 50 microM) to the perfusing medium. Superfusion of the slices with Cs (2 mM) during the 1 Hz stimulation period could both inhibit the maintenance phase of the depression itself and elicit spontaneous rhythmic activity. Cs had no effect on the postsynaptic response to the GABA-B agonist, baclofen. As a major effect of Cs is a block of the hyperpolarization-activated current (Ih), these results suggest the possible involvement of Ih in the maintenance of long-term depression.

2-Amino-5-phosphonovalerate↗
PubMed2000

Ca2+-dependent kinetics of hair cell Ca2+ currents resolved with the use of cesium BAPTA.

Hair cells in the frog semicircular canal, studied by the whole-cell patch-clamp technique, display three distinct Ca2+ currents: two non-inactivating components (L type and R type, the latter termed R2 in the following) and a second R type current (termed R1), which runs down first and inactivates in a Ca2+-dependent fashion. Since intracellular EGTA, up to 5 mM, did not display major effects on such inactivation, we used increasing amounts of BAPTA in the patch pipette, to control [Ca2+]i more efficiently and investigate whether modifications in [Ca2+]i at the cytoplasmic side of the channel affect the inactivation of the RI component and in general the gating of all channel types. The results here reported show that (1) K+ currents heavily contaminate recordings obtained using high concentrations of BAPTA in its commercially available K+ salt form; (2) BAPTA Cs+ salt can be satisfactorily employed to obtain reliable recordings; (3) the kinetics of channel gating and R1-channel inactivation are indeed markedly affected by effectively buffering [Ca2+]i.

Animals↗