Cesium Injection Research Articles

Effects of vasoactive intestinal contractor on voltage-activated Ca2+ currents in feline parasympathetic neurons.

Intracellular current-clamp and single-electrode voltage-clamp techniques were used to study in vitro action potentials and the action of vasoactive intestinal contractor (VIC; 0.03-1 microM) on the high-voltage-activated Ca2+ currents (ICa) of neurons in feline colonic parasympathetic ganglia. In the current-clamp recording mode, action potential amplitude was depressed by cobalt (1 mM) and omega-conotoxin (300 nM) or in nominally Ca(2+)-free Krebs solutions. In the single-electrode voltage-clamp recording mode, the ICa was isolated by blocking the voltage-gated Na+ current with tetrodotoxin (1-3 microM) and by Krebs solutions containing a low Na+ concentration. The voltage-activated K+ currents were blocked by intracellular injection of cesium through a recording electrode filled with 2 M CsCl and external application of tetraethylammonium (30-50 mM) and barium (2 mM). The Ca(2+)-dependent Cl- current was blocked by replacement of Ca2+ (2 mM) with equimolar barium. Anomalous rectification was blocked by external application of 2 mM cesium. The ICa was evoked by depolarizing step commands more positive than -40 mV from holding potentials ranging between -80 and -60 mV. ICa was depressed by cobalt (1 mM), cadmium (100 microM), and omega-conotoxin (500 nM) but not by nifedipine (10 microM), nicardipine (10 microM), and verapamil (10 microM). BAY K 8644 (3-10 microM) also did not affect the ICa. VIC (0.1-1 microM), one of the endothelin (ET) isopeptides, caused an inward current followed by an outward current. The VIC-induced inward and outward currents were associated with an increase and decrease in membrane conductance, respectively. VIC also caused an initial depression followed by a long-lasting augmentation of the ICa. ET-1, ET-2, and ET-3 equally mimicked the action of VIC on both holding current and ICa. These data suggest that VIC activates a receptor-operated channel and modulates the omega-conotoxin-sensitive voltage-activated Ca2+ channels through ETB receptor subtypes of neurons in feline colonic parasympathetic ganglia.

20 years of cesium catalysis for negative ion production in gas discharges (invited)

Cesium catalysis, considerable acceleration of negative ion production in a gas discharge by injecting a small admixture of cesium or other substances with low ionization potential (for example, the first or the second group elements), is used now very widely in ion sources. The cesium injection turns on the catalysis of negative ion production on the electrodes surface, bombarded by particles from discharge plasma. The cesium adsorption significantly increases the probability of the electron capture from the electrode surface to the electron affinity levels of sputtered and reflected particles by decreasing the surface work function from 4–5 eV up to 1.5 eV. It increases considerably negative ion containment in particle flux from the surface. Ion sources using cesium catalysis have been named surface plasma sources (SPS), because for their operation a strong interaction of gas discharge plasma with a surface is very important. However, volume negative ion production depends on cesium admixture and surface processes also. Highly efficient cesium catalysis has been discovered in Novosibirsk Institute of Nuclear Physics on July 1, 1971. During 20 years in many laboratories around the world wide investigations of physics processes in surface-plasma sources have been executed. Various types of SPS, optimized for different applications in accelerators, in plasma physics and thermonuclear research, in technology, have been developed. The distinctive features of physical processes in SPS and technological development for high efficient SPS operation are reviewed in presented papers.

Early and Delayed Afterdepolarizations Associated with Cesium Chloride-Induced Arrhythmias in the Dog

Monophasic action potentials (MAPs) were utilized to examine the basis for cesium-induced arrhythmia in the dog. Cesium chloride (1 mmol/kg i.v.) produced an immediate prolongation of MAP (250 +/- 11 to 396 +/- 34 ms, p less than 0.05). Coupled premature ventricular beats (345 +/- 46 ms) and polymorphic ventricular tachycardia developed in association with early afterdepolarizations during the first 1-3 min after cesium administration. A slowing of the sinus heart rate with vagus nerve stimulation exacerbated the arrhythmia. During the subsequent 7 min, the MAP duration decreased from 396 +/- 34 to 316 +/- 19 ms. At 8-10 min, the premature ventricular beats were associated with delayed afterdepolarizations in the MAP recordings. However, there was no change in the coupling intervals of the premature ventricular beats (351 +/- 29 ms). Ventricular arrhythmias and delayed afterdepolarizations during this phase were exacerbated by increasing the heart rate with atrial pacing. T wave alternans and U wave formation in the ECG were associated with early or delayed afterdepolarizations in MAP. Cesium chloride (1 mmol) injected into the left anterior descending coronary artery produced local MAP prolongation and ventricular bigeminy. Although the MAP duration returned to predrug values after intracoronary cesium injection, the severity of ventricular arrhythmia increased with succeeding doses. These data suggest that early and delayed afterdepolarizations, T wave alterations, and ventricular beats can be dissociated from the initial action potential prolongation with cesium and closely resemble altered calcium transients observed in vitro.

Afterhyperpolarization mechanisms in cat sympathetic preganglionic neuron in vitro.

A long-lasting afterhyperpolarization (AHP) follows the antidromic or current-induced action potential of sympathetic preganglionic neurons (SPNs) studied in slices of cat spinal cord maintained in vitro. Duration and amplitude of the AHP that follows a single spike were 2.8 +/- 0.3 s and 16.0 +/- 0.7 mV (mean +/- SE), respectively. In most cases two components could be distinguished, an initial faster and usually larger component [fast (F) AHP] followed by a slowly decaying component [slow (S) AHP]. An increase in membrane conductance was associated with the AHP. The amplitude of both components increased with membrane depolarization and decreased with hyperpolarization. Both fast and slow component were nullified at a voltage of -90 mV in 3.6 mM K+. Peak AHP amplitude decreased as K+ was increased from 1.5 to 7.0 mM. The null point for both fast (F) AHP and slow (S) AHP shifted in the depolarizing or hyperpolarizing direction when K+ was increased or decreased, respectively. These data suggest that an increase in K+-conductance is the mechanism underlying the AHP. The two components of the AHP could be separated by their differential sensitivity to superfusion with the Ca2+-channel blocker cobalt (2 mM) or with low Ca2+ (0.25 mM). These procedures resulted in an AHP of much shorter duration (330 ms, range 150-600), presumably the FAHP. These observations indicate that a Ca2+-activated K+-conductance is likely to be involved in the generation of the SAHP. The FAHP was depressed during superfusion with tetraethylammonium (TEA) (20 mM) and intracellular cesium injection. The SAHP was enhanced by TEA and enhanced or depressed by cesium. In 3.6 mM K+ the FAHP reversed in polarity at membrane voltages more negative than -90 mV. This component had an approximately linear relation of amplitude to membrane potential. The SAHP did not reverse in most cells. In the few cases in which it reversed, the change in amplitude for a given change in membrane voltage was much smaller on the negative than on the positive side of the null potential. Thus the SAHP shows voltage-dependent, nonlinear characteristics. This difference in behavior of the two components was also observed when the null point was displaced in high or low K+. In the presence of tetrodotoxin (TTX) the AHP persisted in temporal association with a high-threshold, TTX-resistant, cobalt-sensitive spike. During the time course of the AHP the efficacy of synaptic input decreased, suggesting that the AHP has an important role in regulating the firing rate of the SPN.

Dynorphin reduces calcium-dependent action potential duration by decreasing voltage-dependent calcium conductance

The opioid peptide dynorphin decreased somatic calcium-dependent action potential duration in a portion of mouse dorsal root ganglion (DRG) neurons without altering resting membrane potential or conductance. Dynorphin action was antagonized by naloxone. Responses of DRG neurons to dynorphin differed from responses to the opioid peptides leucine-enkephalin, which binds preferentially to delta-opiate receptors, and morphiceptin, which binds preferentially to mu-opiate receptors. Firstly, many DRG neurons responded to dynorphin but not to leucine-enkephalin or morphiceptin. Secondly, dynorphin responses, unlike leucine-enkephalin or morphiceptin responses, persisted following intracellular injection of cesium, a potassium channel blocker. We suggest that dynorphin acts at an opiate receptor distinct from mu- and delta-receptors and that this receptor is coupled to a voltage-dependent calcium channel.

Large scientific releases

Mass-injection experiments in space plasmas have been conducted for the last twenty years. These injections trace or stain chemical or physical processes, facilitating diagnosis of the natural state of the space plasma; artificially perturb the space plasma away from equilibrium, isolating and controlling selected parameters; simulate natural or artificial states of space plasmas; and utilize the advantages of space as a laboratory to study fundamental plasma physics. We use the Lagopedo ionospheric-depletion experiments to illustrate the special operational aspects of active experiments, including weather, logistics, communications, and real-time diagnostics. The various objectives and techniques of mass-injection experiments are described by example. The CAMEO experiment, a thermite barium release from a satellite over the nightside polar cap, is an excellent example of the use of barium injections to trace upward ion acceleration. The Periquito Dos experiment provided a “snapshot” view of convection electric fields in the dayside polar cusp region. Project Waterhole, an artificial depletion of the topside auroral ionosphere, attempted to modify the equilibrium character of the field-aligned currents and apparently shut off the aurora in a small space-time volume. The Trigger experiment is another example of an active perturbation experiment, wherein the auroral ionospheric transverse conductivities were modified via a cesium injection. The Buaro experiment, a shaped-charged barium injection perpendicular to the local geomagnetic field, resulted in an ion-beam/background-plasma system being displaced from equilibrium, permitting diagnostics of collisionless coupling of the ion beam to the background plasma.

Rocket observations of stimulated electron acceleration associated with the Trigger Experiment

Evidence for a strong enhancement of the electron flux associated with a cesium cloud release from the ‘Trigger’ rocket payload, launched from Esrange on February 11, 1977, will be presented. The up to three orders of magnitude enhancement of the electron flux first appeared some ˜150 ms after the cesium injection and prevailed for about 1 s. A remarkable feature of this enhancement is that it was not only field aligned (at 2 keV) in the downward direction, but also in the center of this electron ‘burst’, field‐aligned in the upward direction. A possible interpretation for the quasi periodic modulation of the 2 keV electron flux in the center part of the ‘burst’, may be that a ‘bunch’ of electrons was locally trapped between two potential barriers. From the bouncing period, the velocity of the 2 keV electrons, and the time dispersion versus pitch angle, the altitude as well as the relative thickness of these potential barriers could be estimated. The altitude and the average parallel electric field strength of the upper (accelerating) potential drop was estimated to be around 500 km and ∼60 mV/m, respectively. The strong field alignment of the upward directed electrons suggests that a reflecting potential barrier was located below the rocket altitude (∼162 km). Although the most evident consequence of the cesium release from particle point of view was the very intense and short‐lived burst of accelerating electrons, there were also indications of a more prolonged effect on the high energy particle population (>40 keV).

Comparative myocardial distribution patterns after intracoronary injection of cesium and labeled particles.

Simultaneous coronary artery or left atrial injections of cesium 131 and several 99mTc-labeled suspensions were made in dogs to determine if soluble indicators could replace labeled macroaggregates for myocardial scanning after coronary artery injection. Only very small particles (<35 μ) showed uniform distribution comparable to cesium. Perfusion defects and vascular beds were more discretely outlined with particles after atrial injection, but with arterial injection particle distribution determined by in vitro analysis often was markedly irregular. No significant differences were found in vivo. Ionic radiopharmaceuticals, such as 129CS, can be used as a safe substitute for macro-aggregates for intracoronary administration.