Effect Of Calcium Concentration Research Articles

The effect of calcium concentration on mitochondrial respiratory function in hypotherically perfused kidneys

The effect of calcium concentration on mitochondrial respiratory function in hypotherically perfused kidneys

The effect of calcium concentration on spontaneous ventricular defibrillation and VF threshold.

In order to investigate the influence of the effective refractory period on spontaneous ventricular defibrillation, isolated rat hearts were perfused with Krebs-Henseleit solution containing 0.5, 2.7 and 5.1 mM calcium. After measuring the fibrillation threshold at spontaneous rate (SR), ventricular fibrillation (VF) was induced during basic ventricular pacing of 110% SR, or the highest rate permitting 1:1 electromechanical coupling. The VF threshold was significantly reduced from 13.6 +/- 3.5 to 7.9 +/- 5.3 and 5.1 +/- 3.4 mA at 0.5, 2.7 and 5.1 mM Ca++ concentrations, respectively. The incidence of spontaneous recovery from VF, induced during basic pacing, was 100%, 83% and 50% at calcium concentrations of 0.5, 2.7 and 5.1 mM, respectively, (p less than 0.01 for the incidences at 0.5 mM versus 5.1 mM Ca++). The incidence of spontaneous defibrillation decreased when the hearts were driven rapidly, with spontaneous recovery rates of 92%, 58% and 0% (p less than 0.0001] for corresponding increases in Ca++ concentration. Induced ventricular fibrillation of fine morphology was frequently observed at 5.1 mM Ca++. It appears that progressive impairment of spontaneous defibrillation is caused by an increase in calcium concentration, this effect being more pronounced at high ventricular rates. Variations in the effective refractory period, caused by alterations in extracellular calcium concentration and differences in intracellular Ca++ accumulation, may account for the above results.

Effects of Calcium Concentrations on Initial Growth, Nodulation and Nitrogen Fixation in Soybean Plant

Effects of Calcium Concentrations on Initial Growth, Nodulation and Nitrogen Fixation in Soybean Plant

Effects of some Ca2+ blockers on receptor potentials of crayfish retina.

One drug known to inactivate calmodulin and two others to block Ca2+ channels were applied to isolated superfused retinae of the crayfish Astacus leptodactylus and their influence on the receptor potentials (RP) was studied. Trifluoperazine causes an increase of the amplitude of maximum (h max) of RP and a prolongation of the time of half decrease (t2). Furthermore, trifluoperazine could antagonise the effect of raised calcium concentration of superfusate, which decreases h max and shortens t2 of the RP. Iproveratril and D-600 cause a transient increase and thereafter a progressive decrease of h max of the RP. There is a difference between effects of both drugs on t2 of the RP. The mechanisms of effects of these drugs on the sensitivity of the isolated retina are discussed.

Increased Prostaglandin Synthesis by Low Calcium-Regulated Keratinocytes

The effect of calcium concentration on the in vitro prostaglandin production by murine keratinocytes was studied using radioimmunoassay. Keratinocytes grown in low-calcium medium (0.02 mM) maintained intracellular calcium levels adequate for arachidonic acid metabolism and actually showed increased prostaglandin production. Baseline, unstimulated PGE2 production was 4.5 times higher in cells growing in low- compared to normal-calcium (1.2 mM) medium (p = 0.001). PGF2 alpha production was increased 2.5 times in the low-calcium cells (p = 0.002). The calcium ionophore A23187 and 12-O-tetradecanoyl-phorbol-13-acetate (TPA) exhibited differing calcium requirements for activation of the arachidonic acid pathway. A23187 ionophore stimulated prostaglandin synthesis only in cells growing in normal-calcium medium while TPA stimulated prostaglandin production by both low- and normal-calcium cells. Paradoxically, short-term exposure of low calcium-grown cells to normal-calcium medium abolished the TPA effect. These results suggested that calcium can control arachidonic acid metabolism at a number of regulatory points.

Effect of Calcium Concentration on Growth and Ion Uptake in Soybean Plants in Solution Culture

Summary The effect of calcium solutions of a wide range of concentration (6.20 to 1247 μM) on growth, ion uptake and tissue content of soybean plants [ Glycine max (L.) Merr cv. Amsoy] was studied under controlled ecological conditions. The maximum growth was recorded with 249.5 μM Ca. At concentrations below 24.9 μM, symptoms of Ca deficiency were observed. The uptake of NH 4 and total N content in soybean plants were not affected. At low Ca concentrations (up to 124.7 μM) a stimulatory effect was evident. Uptake and tissue concentration of P was independent of strength of Ca up to 249.5 μM and beyond this range an insignificant decrease was noticed. Potassium uptake and tissue concentration increased up to 249.5 μM Ca followed by a reduction up to the maximum concentration studied (1247 μM). However, the maximum concentration of K in plant material was recorded at lower Ca concentration (124.7 μM). Up to 124.7 μM, calcium increased the rate of uptake as well as the tissue concentration of Mg and further augmentation of the strength of the Ca solution resulted in a decreasing trend. The results observed in this study suggest that balanced nutrient level in the soil and nutrient solution is of paramount importance in the mineral nutrition of soybean plants.

Fixation of Iron Applied as FeEDTA: Effect of Calcium Concentration and Soil Solid Phase

AbstractIron fixation from FeEDTA was measured in three soils at various water contents and Ca concentrations as a function of time for periods up to 30 hours, using a batch technique. In the three soils under study the general pattern of the fixation reaction can be described as a first‐order reaction if adsorption is assumed to be much faster than fixation reaction. The rate constant is markedly affected by Ca concentration: in Rehovot sand and Nazaret clay loam (0 and 61% CaCO3, respectively) the reaction rate constant increases sharply as added Ca increases from 0 to 5 mM, followed by a moderate and more or less linear increase up to Ca concentration of 100mM. In Zophar sandy loam (69% CaCO3), the reaction rate constant shows a maximum at Ca concentration of 50mM and then decreases.In Rehovot sand and Nazaret clay loam the fixation process can be described by two independent first‐order reactions taking place simultaneously on the solid phase surface and in the liquid phase. Zophar sandy loam does not fit this model. It is suggested that the solid surface area affects the fixation reaction in addition to the effects of pH and Ca concentration.The effect of Ca on Fe‐FeEDTA fixation is discussed in connection to average and local Ca concentrations. High Ca concentrations near the root surface, formed due to transpiration stream, constitute a “chemical barrier” for the movement of Fe‐FeEDTA toward the root.

Lack of effect of hypocalcemia on renal phosphate handling.

A possible effect of decreased plasma ionized calcium concentration on renal phosphate handling was investigated in dogs with control of parathyroid hormone. Intrarenal artery infusion of either EDTA or sodium citrate decreased ionized calcium concentration 25 per cent in renal vein blood but had no significant effect on fractional phosphate excretion. Similarly, intravenous infusion of chelators had no significant effect on fractional phosphate excretion. It is concluded that acute decreases in ionized calcium have no significant effect on the renal handling of phosphate.

The effect of calcium concentration on ACTH stimulation of steroidogenesis in mouse adrenal tumor cells.

AbstractCalcium is required for ACTH stimulated steroidogenesis in adrenal tumor cells in tissue culture. In the absence of calcium, the dose of ACTH required to induce half maximum steroidogenesis was increased 30 fold. In contrast to intact adrenal glands or isolated adrenal cells, high doses of ACTH (50 mU/ml) maximally stimulated steroidogenesis in the absence of calcium. Growth for up to six days in medium with low calcium did not affect basal or ACTH induced steroidogenesis. The addition of calcium to cells incubated with ACTH produced a maximum steroidogenic response in 15 minutes. In contrast to intact adrenal glands, calcium is not required for adenosine‐3′,5′‐cyclic monophosphate (cyclic AMP) stimulated steroidogenesis in adrenal tumor cells. These experiments support the concept that calcium is important at the level of ACTH‐membrane receptor site interaction or activation of adenyl cyclase in adrenal tumor cells.

Total body calcium and long-term calcium balance in chronic renal disease.

Abstract Renal bone disease is a common cause of morbidity in patients with end-stage renal failure undergoing dialysis. The natural history of this entity and the effect of dialysate calcium concentrations have been studied in 26 chronic dialysis patients by total body calcium (TBC) measurement with neutron activation analysis (NAA), bone biopsies, calcium absorption, hand radiographs, serum chemistry, and skin calcium determinations. Calcium balance was measured by serial NAA over intervals up to 27 months. Total body calcium (TBC) ranged from 503 to 1,392 Gm. and in the 24 males averaged 1,116 Gm. or 96 ± 12 per cent of predicted normal. Bone fractures occurred in 5 of 8 patients with TBC less than 90 per cent of predicted normal and in only 2 of 16 patients with TBC greater than 90 per cent of predicted normal. The relationship of TBC and calcium balance with bone biopsy suggested that osteomalacia and fibrosis may be different disease entities. Osteomalacia was characterized by low TBC (87 per cent of predicted normal) and progressively negative calcium balance (−5.0 per cent TBC per year). Fibrosis was characterized by normal to high TBC (106 per cent of predicted normal) and stable calcium balance (−0.2 per cent TBC per year). A change in dialysate calcium from 3.0 to 4.0 mEq. per liter appeared to have a beneficial effect on calcium balance. Eleven patients observed on a dialysate bath of 3.0 mEq. per liter calcium over 12.2 patient-years experienced a cumulative TBC loss of 34.1 per cent. On the other hand, 10 patients observed on a 4.0 mEq. per liter calcium dialysate over 10.3 patient-years experienced a cumulative gain in TBC of 2.3 per cent.

The effect of calcium concentration on calcium uptake by bone cells treated with thyrocalcitonin (TCT) hormone.

The effect of calcium concentration and thyrocalcitonin (TCT) on the uptake of calcium by bone cells in vitrowas studied. Both TCT and elevated calcium concentrations caused an accumulation of calcium in the cells. Given in conjunction, the effect of the two was larger than the separate effects added together. The amount of radiocalcium released by the cells during incubation was inversely related to the amount of calcium accumulated in the cells. The findings can be explained by assuming two types of calcium fluxes between medium and cells: a) a concentration dependent influx, and b) a constant rate calcium extrusion process subject to TCT inhibition. (Endocrinology92: 550O, 1973)

Erratum

In “Effect of Calcium Concentration on Inhibitors of Hemagglutination of Rubella Virus” by Stella A. Biano, Cecil C. Jenkins, and Joan B. Daniels (April, 1971), page 421, the last sentence on page 421 (continued on page 422) should read: “Supernates from the cell cultures, which may have a higher content of calcium, were not used as a source of antigen.”

Effect of calcium concentration on transmembrane potentials and contraction of myocardial cells

Effect of calcium concentration on transmembrane potentials and contraction of myocardial cells

The effects of calcium on isometric tension in isolated heart muscle during coupled pacing

The effects of calcium concentration on the positive inotropic effects of coupled pacing were studied in a myograph. An increase in calcium concentrations in the muscle bath up to levels of 15.6 mM. per liter resulted in the development of greater isometric tension in guinea pig ventricular strips, but the increment in tension produced by coupled pacing fell progressively at all calcium concentrations above 2.6 mM. per liter. The delay between the basic stimulus and the coupled stimulus to produce maximal enhancement of contractility during coupled pacing decreased progressively with higher concentrations of calcium.

Effect of calcium concentration on the transmembrane potentials of Purkinje fibers.

The effects of variation in calcium concentration on the action potential of Purkinje fibers isolated from the dog heart were studied. Action potentials recorded during perfusion with Tyrode solution containing 2.7 mM calcium chloride were compared with those recorded during subsequent perfusion with solutions containing 0.675 (1/4X), 1.35 (1/2X), 5.4 (2X), or 10.8 (4X) mM calcium chloride. In both 1/2X and 1/4X solutions, the time required to repolarize to minus 60 mv and the duration of the action potential were increased. There were significant decreases in the slopes of phases 2 and 3 and the terminal phase of repolarization, while the slope of phase 1 increased. In 2X or 4X solutions, repolarization was speeded mainly by an earlier onset of phase 3. As a result the time to repolarize to minus 60 mv and the duration of the action potential were decreased significantly. The slope of phase 1 decreased significantly in 4X solution. In both high calcium solutions the rate and magnitude of diastolic depolarization increased. It was shown that the rate of the calcium-enhanced diastolic depolarization was dependent on the stimulus rate. The possible role of these changes in transmembrane potential in causing the ventricular arrhythmias following CaCl 2 infusion in intact animals is discussed.

Viscosity and Flocculation of Heated β-Lactoglobulin Solutions: Effect of Calcium Concentration and pH

Summary The effect of calcium concentration, pH, and heat on the physical properties of β -lactoglobulin solutions was investigated. Viscosity, light transmission, and precipitation were measured. The dependence of viscosity on pH and the effect of certain α-amino group reagents suggested that α-amino groups assist in the binding of calcium ions. Precipitation in calcium-containing heated β -lactoglobulin solutions was sharply dependent on pH; the lower the pH, the smaller the concentration of calcium required. Calcium appears to function in large part to bring about an isoelectric precipitation by neutralizing negatively charged groups. The effects of heat on β -lactoglobulin solutions are discussed in relation to the heat stability of milk.