Potassium concentration, effect

Cao, W., Tibbitts, T. W. (1991a). Potassium concentration effect on growth, gas exchange, and mineral accumulation in potatoes. J Plant Nutr, 14, 525-527. 

For analysis, let us assume that the concentration profile migrates inward as shown in Figure 16.1b with an error-function profile whose width increases in proportion to (time), and let us assume for a start that the stress state has no effect on the migration of potassium. Let us assume that the compressive stress at any point tends to rise because of this potassium concentration effect but tends to fall because of creep or relaxation of the glassy host. And let us assume that at small distances (less than 1 pm) from the surface, stress is relieved also by self-diffusion of the glass, so that right... 

The addition of potassium to Fe single crystals also enliances the activity for ammonia synthesis. Figure A3.10.19 shows the effect of surface potassium concentration on the N2 sticking coefficient. There is nearly a 300-fold increase in the sticking coefficient as the potassium concentration reaches -1.5 x 10 K atoms cm ... 

Potassium-sparing by diuretic agents, particularly spironolactone, enhances the effectiveness of other diuretics because the secondary hyperaldosteronism is blocked. This class of diuretics decreases magnesium excretion, eg, amiloride can decrease renal excretion of potassium up to 80%. The most important and dangerous adverse effect of all potassium-sparing diuretics is hyperkalemia, which can be potentially fatal the incidence is about 0.5% (50). Therefore, blood potassium concentrations should be monitored carehiUy. 

However, although high potassium concentration was thought essential in early experimental work (Acquatella etcd., 1972), Fuller and Pe (1976) reported that potassium concentrations much higher than normal plasma levels led to poor renal function. A number of more recent studies have claimed that solutions containing high concentrations of sodium ions were equally or even more effective than those with high potassium (Moen et al., 1989 Sumimoto etal., 1989 Marshall etal., 1991). 

Figure 1. Composition and Concentration Effects of Potassium Based Clear Well Fluids on Core Permeabilities.

In contrast to the metabotropic effects described for presynaptic kainate receptors in CA1 (90,94), the effects of kainate in CA3 appear to be mediated by direct depolarization of the presynaptic terminals. The kainate-induced facilitation is not sensitive to antagonists of other receptors (e.g., GABAb), and can be mimicked by elevating the extracellular potassium concentration (77,100). It has been proposed that the facilitation is owing to increased calcium influx that is induced by modest depolarization of the terminals by kainate receptors, whereas a strong depolarization, in response to activation of a larger receptor population, causes the sodium channels to inactivate and thereby depresses transmission (77,84,88,100-102). 

The side-effects of cardiac glycosides are mostly caused by electrophysiological/neuronal phenomena. Gastro-intestinal adverse reactions are probably triggered by effects on the central nervous system. Various types of cardiac arrhythmias are caused by the influence of the drugs on nodal tissues in the heart. The risk of arrhythmia is strongly enhanced by low plasma potassium concentrations. 

Parenteral /32-agonists such as albuterol (salbuta-mol) increase the activity of the membrane sodium-potassium ATPase, and so increase potassium entry into cells. Nebulized or infused albuterol (salbutamol) significantly lowers serum potassium concentration over 5 hours. A suitable initial dose of nebulized albuterol is 5 mg in adults. It can provoke tremor and tachyarrhythmia, and it is desirable to monitor cardiac rhythm during nebulization. The combination of nebulized albuterol (salbutamol) with infusion of insulin + glucose is more effective than the infusion alone. 

The serum potassium concentration can be effectively reduced by dialysis, and this is often indicated in patients presenting with renal failure and acute hy-perkaleamia. However, dialysis may take some time to institute, especially if the patient has to be transferred to a specialist centre. Calcium polystyrene sulphonate is often used, but there is little evidence of efficacy and its use is not entirely without risk. 

Activated charcoal adsorbs salicylate effectively, and has been given in repeated oral doses (50 g 4 hourly) to enhance clearance, although its effect on outcome is unknown. Fluid and electrolyte replacement are important and special care should be taken to maintain normal potassium concentrations. Patients with signs of poisoning, especially when plasma salicylate concentration exceeds 500 mg/1, should receive specitic elimination therapy. 

Dofetilide blocks IKr in all myocardial tissues. It blocks open channels, and its binding and release from the channels is voltage dependent. The effects of dofetilide are exaggerated when the extracellular potassium concentration is reduced, which is important, as many patients may be receiving diuretics concurrently. Conversely, hyperkalemia decreases the effects of dofetilide, which may limit its efficacy when local hyperkalemia occurs, such as during myocardial ischemia. Dofetilide demonstrates reverse use dependence, that is, less influence on the action potential at faster heart... 

The effect of potassium. Take five replicate emission readings of each of the six potassium standards. Remember to zero the instrument between each standard while aspirating a blank. Calculate the mean emission and RSD for each standard and plot a graph of sodium emission intensity against potassium concentration. The RSD is defined as standard deviation (s) of the emission intensities divided by the mean emission intensity (jf)[RSD = (s/x) x 100]. 

Additive effects with other agents increasing serum potassium concentration. May alter renal excretion of substances other than potassium (eg, digoxin, hydrogen ions). 

Because of the disadvantages of the ICP systems listed above, we chose to do our study on the simpler less expensive sequential direct current plasma system (27, 59-65) It is well to recognize that in any choice of this kind trade-offs may become necessary. For example, the DC plasma is subject to more or less severe matrix effects, and these must be accounted for in setting up the methodology (28 ). These effects are illustrated in Figures 1 and 2 which show the influence of the large potassium concentrations on both the atom and ion lines of barium. 

A 3 per cent solution of hydrazoic acid (synthesis 26A) is neutralized with an aqueous solution of pure potassium hydroxide. The resulting solution of potassium azide is concentrated on the steam bath to incipient crystallization. The solution is then made slightly acid with hydrazoic acid to replace the hydrogen azide lost by hydrolysis. A volume of ethyl alcohol twice that of the solution is added, and the solution is cooled in an ice bath. Since the solubility in alcohol of the alkali and alkaline earth azides is very slight (see table below), precipitation in the form of a white microcrystalline salt takes place readily. From 90 to 95 per cent recovery of the theoretical quantity of potassium azide can be effected. The precipitated azide is filtered on a Buchner funnel and washed with cold absolute alcohol and then with ether. Any traces of adhering solvent may be removed in a vacuum desiccator. In a typical run, 300 ml. of a solution of hydrazoic acid containing 8.5 g. of HN3 was neutralized with potassium hydroxide, and the isolation of potassium azide effected as indicated above. Yield 14.7 g. (91.5 per cent) KN3. 

The developed cesium and potassium extraction model, based on extraction data obtained from simple aqueous media, was tested to ensure the validity of the prediction for the cesium extraction from actual waste.112 The predicted values agreed with the measured values for the simulants predicted values also agreed, with some exceptions, with measured values for the tank wastes. Discrepancies were attributed, in part, to the uncertainty in the cation/anion balance in the actual-waste composition, but likely more so to the uncertainty of the potassium concentration in the waste, given the demonstrated large competing effect of this metal on cesium extraction. It was demonstrated that the upper limit for the potassium concentration in the feed should not exceed 0.05 M, in order to maintain suitable cesium distribution ratios. 

As ice crystals grow in the freezing system, the solutes are concentrated. In addition to increased ionic strength effects, the rates of some chemical reactions—particularly second order reactions—may be accelerated by freezing through this freeze-concentration effect. Examples include reduction of potassium ferricyanide by potassium cyanide (2), oxidation of ascorbic acid (3), and polypeptide synthesis (4). Kinetics of reactions in frozen systems has been reviewed by Pincock and Kiovsky (5). 

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