Serum ionized calcium by specific ion electrode

Calcium Regulation of Bacterial Virulence

Calcium (Ca²⁺) is a universal signaling ion, whose major informational role shaped the evolution of signaling pathways, enabling cellular communications and responsiveness to both the intracellular and extracellular environments. Elaborate Ca²⁺ regulatory networks have been well characterized in eukaryotic cells, where Ca²⁺ regulates a number of essential cellular processes, ranging from cell division, transport and motility, to apoptosis and pathogenesis. However, in bacteria, the knowledge on Ca²⁺ signaling is still fragmentary. This is complicated by the large variability of environments that bacteria inhabit with diverse levels of Ca²⁺. Yet another complication arises when bacterial pathogens invade a host and become exposed to different levels of Ca²⁺ that (1) are tightly regulated by the host, (2) control host defenses including immune responses to bacterial infections, and (3) become impaired during diseases. The invading pathogens evolved to recognize and respond to the host Ca²⁺, triggering the molecular mechanisms of adhesion, biofilm formation, host cellular damage, and host-defense resistance, processes enabling the development of persistent infections. In this review, we discuss: (1) Ca²⁺ as a determinant of a host environment for invading bacterial pathogens, (2) the role of Ca²⁺ in regulating main events of host colonization and bacterial virulence, and (3) the molecular mechanisms of Ca²⁺ signaling in bacterial pathogens.

Measurement of Total, Ultrafilterable and Ionised Serum Calcium

The development and assessment of methods for measurement of total, ultrafilterable and ionised serum calcium is given. An existing fluorimetric technique for total calcium has been automated and modified for routine use. A device for rapidly preparing serum ultrafiltrates has been developed and an electrometric method for ionised calcium measurement assessed. Values in normal subjects are given for all three fractions and compared with the findings of other workers.

A calculation model for serum ionized calcium based on an equilibrium equation for complexation

Measurement of ionized calcium is more important than measurement of total calcium in serum samples. In the present study, equations were derived from complexation and acid dissociation equilibrium equations, and were used to determine the concentration of ionized calcium from the observed serum concentrations of total calcium, albumin, total protein, and inorganic phosphate. The ionized calcium concentration was calculated in 67 serum samples from healthy subjects and 34 outpatients previously identified as having abnormal serum calcium levels. The correlation coefficient between our method (y) and the calcium-ion-selective electrode method (x) was 0.953 and the linear regression equation was y = 0.97x at pH 7.4 with a factor of α = 0.21, which was based on the differences between the concentrations of calcium phosphorus compounds obtained by the electrode method and by calculation. The developed calculation is as useful and accurate as the electrode method, and therefore extremely useful for clinical diagnoses.

Effects of YM175, a new-generation bisphosphonate, on hypercalcemia induced by tumor-derived bone resorbing factors in rats

YM175 (disodium cycloheptylaminomethylenediphosphonate monohydrate) is a new-generation bisphosphonate with stronger inhibitory activity on bone resorption than first-generation bisphosphonates. In the present study, the effect of YM175 on hypercalcemia induced in rats by single administration of either parathyroid hormone-related protein (PTHrP) or concomitant administration of PTHrP and interleukin 1beta (IL-1beta) was investigated. YM175 (0.01-1 mg/kg, i.v.) inhibited the increase in serum free calcium concentration induced by continuous administration of PTHrP alone (3 microg/rat/day, s.c., 7 days) dose-dependently. The inhibitory effect of YM175 appeared the day after administration and remained 3 days after administration. The effect of YM175 reached a maximum 2 days after administration, at which time the ED50 value of YM175 was calculated to be 0.041 mg/kg, i.v., revealing a potency approximately 50- and 10-fold stronger than those of either pamidronate or alendronate, respectively. In contrast, elcatonin (1-10 units/kg, s.c.) only transiently inhibited PTHrP-induced free calcium increase. YM175 (0.1-3 mg/kg, i.v.) also inhibited the increase in the serum free calcium concentration induced by continuous concomitant administration of both PTHrP and IL-1beta in a dose-dependent manner. These results indicated that YM175 is expected to be a useful drug for hypercalcemia associated with malignant tumors due to its efficacy and range of effect.

Chronic respiratory alkalosis induces renal PTH-resistance, hyperphosphatemia and hypocalcemia in humans

The effects of chronic respiratory alkalosis on divalent ion homeostasis have not been reported in any species. We studied four normal male subjects during a four-day control period (residence at 500 m), during six days of chronic respiratory alkalosis induced by hypobaric hypoxia (residence at 3450 m), followed by a six-day eucapnic recovery period (500 m) under metabolic balance conditions. Chronic respiratory alkalosis (delta PaCO2, -8.4 mm Hg, delta[H+] -3.2 nmol/liter) resulted in a sustained decrement in plasma ionized calcium concentration (delta[IoCa++]p, -0.10 mmol/liter, P less than 0.05) and a sustained increment in plasma phosphate concentration (delta[PO4]p, +0.14 mmol/liter, P less than 0.005) associated with increased fractional excretion of Ca++ (+0.5%, P less than 0.005), decreased phosphate clearance (-6.1 ml/min, P less than 0.025) and decreased excretion of nephrogenous cAMP (-1.5 nmol/100 ml GFR, P less than 0.0025). Urinary phosphate excretion decreased by 15.4 mmol/24 hr on day 1 of chronic respiratory alkalosis (P less than 0.0025), but returned to control values by day 6 despite hyperphosphatemia. Serum intact [PTH] did not change. Sustained hypomagnesuria (-0.8 mmol/24 hr, P less than 0.05) occurred during chronic respiratory alkalosis and was accounted for, at least in part, by decreased fractional excretion of Mg++ (-0.7%, P less than 0.05) in the absence of change in plasma magnesium concentration. Serum 1,25(OH)2D levels were unchanged by chronic respiratory alkalosis. In conclusion, the decrease in nephrogenous cAMP generation despite unchanged serum intact PTH concentration suggests that chronic respiratory alkalosis results in impaired renal responsiveness to PTH as manifested by alterations in PTH-dependent renal calcium and phosphate transport.(ABSTRACT TRUNCATED AT 250 WORDS)

A comparison of serum ionized calcium in arterial and mixed venous blood during CPR

Changes in the actual ionized calcium level (aCa2+) of serum in arterial and mixed venous blood during CPR were investigated in 22 patients with intrinsic cardiopulmonary arrest. Measurements were carried out at an average of 5.4 +/- 0.6 minutes (group 1) and 30 minutes (group 2) after the beginning of CPR, using simultaneously taken blood samples. The aCa2+ of groups 1 and 2 revealed no difference between arterial and mixed venous bloods. As CPR proceeded, the aCa2+ of both bloods diminished, and group 2 had a significantly lower value than did group 1 (arterial blood: 2.36 +/- 0.04 mEq/L vs 2.09 +/- 0.09 mEq/L, P less than .01; mixed venous blood: 2.37 +/- 0.05 mEq/L vs 2.13 +/- 0.06 mEq/L, P less than .001). Conversely, pH values were significantly higher for arterial blood rather than for mixed venous blood, but there was no significant change in pH between groups 1 and 2 (arterial blood, 7.11 +/- 0.05 vs 7.14 +/- 0.04; mixed venous blood, 6.93 +/- 0.04 vs 6.98 +/- 0.03). Furthermore, an analysis of the aCa2+ serum level measurements was carried out in relation to survivors and nonsurvivors and to the presence or absence of a witness at the time of the cardiac arrest. In all groups, there was no difference in aCa2+ between arterial and mixed venous blood. As CPR proceeded, however, the aCa2+ showed a significant decrease in all groups. This decrease was accompanied by a pH increase in arterial blood of patients with a witnessed cardiac arrest and in mixed venous and arterial blood of survivors.

Variation in serum ionized calcium on cardiopulmonary resuscitation

Changes in serum ionized calcium (Ca(++)) levels during cardiopulmonary resuscitation (CPR) and before and after CaCl(2) administration have been examined and investigated in 30 patients with cardiopulmonary arrest on arrival (dead on arrival patients) when a significant negative correlation was found to exist between the transportation time and aCa(++), as the aCa(++) level decreased with an increase in the transportation time. Upon arrival, the pH had fallen due to acidosis so that aCa(++) and cCa(++) levels were virtually normal. After admission, the pH rose as a result of CPR, resulting in a significant drop in both Ca(++) levels, so that in most cases resuscitation was not possible. Those successfully resuscitated took over 60 min to return to normal Ca(++) levels. Administration of approximately 6.6 mg/kg of CaCl(2) led to significant increases in aCa(++) and cCa(++) to essentially normal levels, even with some patients recording extremely elevated Ca levels, even with some patients recording extremely elevated Ca levels. However, the success rate of resuscitation was not found to show any significant difference according to whether CaCl(2) had or had not been administrated.Thus, it is felt necessary to re-examine the use of calcium chloride on CPR.

Plasma ionized calcium during open-heart surgery

Plasma ionized calcium has been measured in eighteen patients undergoing open heart surgery. No change in ionized calcium concentration was found during the period of cardiopulmonary bypass. In the early postbypass period, a wide range of ionized calcium concentrations was found, but this did not obviously affect myocardial performance. Factors influencing the ionized calcium concentration under these circumstances are discussed.

Free ionised calcium--a critical survey

It is our aim to summarise and discuss procedures for the evaluation of the concentration of free ionised calcium in serum or plasma. Stress is laid upon the interrelations and relative validity of the most common algebraic expressions to appraise the calcium status. The multitude of formulae proposed in the literature are, by mathematical discussion, reduced to variations on a single theme. A second topic is the direct potentiometric measurement of free ionised calcium concentration. Finally we review the literature on the clinical utility of measuring or calculating the free ionised calcium concentration.

The effect of temperature on plasma ionized calcium measured in whole blood in vitro

Plasma calcium ion concentration (cCa2+) in samples from 50 healthy volunteers was measured at four temperatures (21, 26, 31 and 37 degrees C) using a calcium electrode based on a neutral carrier ligand. A small negative correlation was found between temperature and cCa2+, the coefficient being -0.0017 mmol . l-1 . degrees C-1 (P less than 0.001). The significance of this in clinical, physiological and instrumentation fields is discussed. The effect on measured cCa2+ of overnight storage at 4 degrees C was slight, but did increase the variance of the results. It is suggested that the most accurate results of cCa2+ will be obtained from fresh samples measured at body temperature.

Calcium measurements in serum and plasma--total and ionized

This article will review the methods currently employed for measuring the concentrations of total and ionized calcium in serum or plasma. As far as total calcium is concerned, various techniques such as atomic absorption spectrometry, spectrophotometry, fluorometry, complexometric titration, and flame photometry will be described and compared. Particular emphasis will be given to the accuracy and precision of each technique. Possible sources of error and interfering agents will be identified and the various procedures for the taking and handling of blood samples evaluated. Inter-laboratory variation in the measurement of calcium will be studied. An assessment will be made of a new reference method for measuring total calcium in serum using isotope-dilution mass spectrometry. The usefulness of the total calcium measurement in clinical medicine will be briefly discussed. Within the last decade the refinement of spectrophotometric techniques and the improvements in ion-selective electrode technology have revolutionized the measurement of ionized calcium in serum, such that it may now be possible to replace total calcium measurements with ionized calcium measurements on a routine basis. The various techniques currently in use for measuring ionized calcium will be described and evaluated. Particular attention will be paid to the preparation of standards, the procedures for taking blood samples, and the handling of the samples prior to and during measurement. An assessment of the relative value of measuring total and ionized calcium will be presented.

Determination of blood ionized calcium in a large segment of the normal adult population

In two different laboratories ionized calcium was determined by use of a calcium selective electrode system of recent design in specimens of whole blood drawn from a total of 100 volunteers. Identical mean values were obtained in each laboratory. A small standard deviation was found supporting the view that [Ca2+] is normally maintained within a narrow range. Ancillary factors in [Ca2+] determination were evaluated, including effects of in-vivo produced changes in pH, and effects of addition of small amounts of heparin to the whole blood sample. A veno-arterial difference in [Ca2+] was insignificant.

An improved procedure for the electrochemical determination of serum ionized calcium

The "Orion model 99-20 serum calcium flow-through system" has been rendered insensitive to protein poisoning by the plascing of a dialysis membrane in front of the electrode membrane, making the addition of trypsin and triethanolamine to standards unnecessary. Flow dependency of the results obtained has been investigated.

Serum ionized calcium by electrodes: new technology and methodology

We report experience measuring serum ionized calcium (Ca2+) with new solid-state, specific calcium ion dip electrodes in a commercially available system for automated electrode measurments which permits stable measurements on thirty samples with up to six different electrodes simultaneously. The system provides electrostatic shielding, temperature regulation at 37degreeC, and adjustment of serum pH with CO2 gas, thereby making practical the use of serum standards and routine measurements on sera. When the electrodes are used with the rest of the measuring system and with serum standards, the system provides serum Ca2+ measurements with high precision (C.V. of 0.7%) and the calcium electrodes maintain good slopes for 50 to 150 hours of cumulative wet immersion. Response to new calcium activity is rapid, and wide variations in serum Ca2+ are readily measured.

The effects in the rat of varying intakes of dietary calcium, phosphorus, and hydrogen ion on hyperparathyroidism due to chronic renal failure

Renal failure of 4 wk duration in rats led to parathyroid enlargement, increased bone resorption, and decreased tubular reabsorption of phosphate by the remnant kidney. The degree of hyperparathyroidism was influenced by each of the three dietary factors investigated. In the first study increasing calcium intake reduced the size of the parathyroids by increasing calcium and reducing phosphate absorption. In the second study phosphate intake was linearly related to parathyroid gland size in the uremic animals and associated with rising plasma phosphate levels. In the last study acidosis led directly to increased bone resorption but small parathyroid glands associated with elevated ionized calcium levels. Alkalosis lowered the serum ionized calcium and led to parathyroid enlargement and the expected associated findings. It was shown that parathyroid weight reflected both metabolic activity as judged by amino acid uptake, and the content of immunoassayable parathyroid hormone. In all studies gland weight was inversely related to serum ionized calcium.