Measurement of ionized calcium in human plasma with a calcium selective 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.

Determination of Plasma Calcium Fractions

A simple, precise, and sensitive method is described for the determination of ionised calcium in plasma at normal body temperature and pH, using an ultrafiltrate of the plasma. This technique is based on a two-wave-length (480 nm, 550 nm) spectrophotometric method, using pH independent dye ammonium tetramethylmurexide (ATM). By this method, the normal (mean + 2 S.D.) plasma ionised calcium in 19 normal subjects is 1.04 + 0.14 mmol/l which is similar to some of those reported for ion-selective electrode measurements.

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.

Anesthetics and anticoagulants used in the preparation of rat platelet-rich-plasma alter rat platelet aggregation

Aggregation of platelets in heparin- and citrate-anticoagulated platelet-rich-plasma (PRP) from rats anesthetized with methoxyflurane (M), diethyl ether (E), acepromazine/ketamine (A/K), or sodium pentobarbital (P) is described, as are platelet counts. Platelet counts were highest in heparin- or citrate-PRP from E and A/K anesthetized rats. Collagen and arachidonic acid (AA) induced aggregation in heparin-PRP only, and ADP induced greater aggregation in heparin-PRP than in citrate-PRP. Differences between citrate-PRP and heparin-PRP are probably due to citrate inhibition of platelet aggregation, since addition of citrate to heparin-PRP decreased aggregation, while addition of heparin to citrate-PRP did not alter aggregation. Aggregation of hirudin-PRP was slightly less than heparin-PRP. Anesthetics affected rat platelet aggregation: the rank order of the maximal extent of ADP-induced aggregation in citrate-PRP was M greater than E = A/K greater than P, and that for AA and collagen in heparin-PRP was E = A/K greater than M = P. The correlation between the effect of the anesthetics and activation of the sympathoadrenal system is discussed. It appeared that of the commonly used anticoagulants and anesthetics, heparin and methoxyflurane had the least influence on rat platelet aggregation.

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.

A simplified method for measurement of Ca++-activity in serum, using serum-monovettes and a Ca++-selective disk-electrode

A simplified method for the anaerobic measurement of ionized calcium in serum of venous blood by use of ion-selective electrodes--the monovette-technique--is described. For estimation of Ca++ a new electrode type--the disk-electrode (11, 12, 13, 14)--charged with a synthetic, electrically neutral Ca++-carrier of the octandioic acid-type (1), is tested.

Determination of serum ionised calcium by ion-exchange electrode in normal subjects

Serum ionised calcium concentration [Ca2+] was measured with a calcium selective electrode in 65 normal people. A mean value of 1.06 mmol/l (+/- 0.04 S.D.) with an actual range of 0.97 to 1.13 mmol/l was obtained. Serum samples refrigerated at 4 degrees C for 24 h were satisfactory for analysis. Storage of whole blood samples for 6 h at room temperature before separation caused a very small error (+0.04 mmol/l). Mean results and ranges were similar in males and females and there was no significant correlation with age. No significant change in serum [Ca2+] was found following a normal meal. Serum [Ca2+] and total serum calcium showed a very slight correlation (r = 0.35). The method is reproducible and sensitive.

[Investigations on the performance of calcium selective disc-electrodes with electrically charged and neutral ligands in anaerobic serum measurements (author's transl)]

Anaerobically prepared serum samples from healthy subjects were simultaneously analysed for Ca++ in a flow-through-system of three ion selective disc-electrodes (electrochemical multimeasurementsystem). Two of the sensors contained electrically charged ligands, the third contained a neutral carrier. With neutral carriers an improvement of performance was noted in that there was a large increase in selectivity toward H+- and NH+4-ions and a distinct enhancement of reproducibility.

Stimulatory effect of pancreozymin-cholecystokinin on calcium secretion in pancreatic juice of dogs

In four dogs with a permanent duodenal Thomas fistula the secretion of calcium, sodium, potassium, protein, and two pancreatic enzymes in pancreatic juice was studied. Infusion of secretin led to a decrease in concentration of calcium and of protein with increasing rates of fluid production. Pancreozymin-cholecystokinin was given in single injections superimposed on the secretin-stimulated flow of juice. This hormone stimulated the secretion of both calcium and enzyme protein in a parallel and closely correlated fashion. The secretion of this protein-bound calcium fraction I is assumed to occur in the acinar cell. A calcium fraction II, which was independent of protein secretion and pancreozymin stimulation, was demonstrated in concentrations of about 0.4 to 0.6 m-equiv/l. This fraction is thought to originate in the interstitial fluid. The secretion of two calcium-containing fluids is in accordance with the two-component theory of secretion proposed by Hollander and Birnbaum (1952).