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PubMed1964

[PAGET'S DISEASE].

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Calcium Metabolism Disorders↗
PubMed1990

Ion microscopic imaging of calcium transport in the intestinal tissue of vitamin D-deficient and vitamin D-replete chickens: a 44Ca stable isotope study.

The intestinal absorption of calcium includes at least three definable steps; transfer across the microvillar membrane, movement through the cytosolic compartment, and energy-dependent extrusion into the lamina propria, Tracing the movement of calcium through the epithelium has been hampered by lack of suitable techniques and, in this study, advantage was taken of ion microscopy in conjunction with cryosectioning and use of the stable isotope 44Ca to visualize calcium in transit during the absorptive process. The effect of vitamin D, required for optimal calcium absorption, was investigated. Twenty millimolar 44Ca was injected into the duodenal lumen in situ of vitamin D-deficient and vitamin D-replete chickens. At 2.5, 5.0, and 20.0 min after injection, duodenal tissue was obtained and processed for ion microscopic imaging. At 2.5 min. 44Ca was seen to be concentrated in the region subjacent to the microvillar membrane in tissue from both groups. At 5.0 and 20.0 min, a similar pattern of localization was evident in D-deficient tissues. In D-replete tissues, the distribution of 44Ca became more homogenous, indicating that vitamin D increased the rate of transfer of Ca2+ from the apical to the basolateral membrane, a function previously ascribed to the vitamin D-induced calcium-binding protein (28-kDa calbindin-D). Quantitative aspects of the calcium absorptive process were determined in parallel experiments with the radionuclide 47Ca. Complementary information on the localization of the naturally occurring isotopes of calcium (40Ca) and potassium (39K) is also described.

Animals↗
PubMed1984

Calcium release from sarcoplasmic reticulum of normal and dystrophic mice.

Contraction of skeletal muscle is triggered by release of calcium from the sarcoplasmic reticulum. In this study, highly purified normal and dystrophic mouse sarcoplasmic reticulum vesicles were compared with respect to calcium release characteristics. Sarcoplasmic reticulum vesicles were actively loaded with calcium in the presence of an ATP-regenerating system. Calcium fluxes were followed by dual wavelength spectrophotometry using the metallochromic indicators antipyrylazo III and arsenazo III, and by isotopic techniques. Calcium release from sarcoplasmic reticulum vesicle was elicited by (a) changing the free calcium concentration of the assay medium (calcium-induced calcium release); (b) addition of a permeant anion to the assay medium, following calcium loading in the presence of a relatively impermeant anion (depolarization-induced calcium release); (c) addition of the lipophilic anion tetraphenylboron (TPB-) to the assay medium and (d) using specific experimental conditions, i.e. high phosphate levels and low magnesium (spontaneous calcium release). Drugs known to influence Ca2+ release were shown to differentially affect the various types of calcium release. Caffeine (10 mM) was found to enhance calcium-induced calcium release from isolated sarcoplasmic reticulum. Ruthenium red (20 microM) inhibited both calcium-induced calcium release and tetraphenylboron-induced calcium release, and partially inhibited spontaneous calcium release and depolarization-induced calcium release. Local anesthetics inhibited spontaneous calcium release in a time-dependent manner, and inhibited calcium-induced calcium release instantaneously, but did not inhibit depolarization-induced calcium release. Use of pharmacological agents indicates that several types of calcium release operate in vitro. No significant differences were found between normal and dystrophic sarcoplasmic reticulum in calcium release kinetics or drug sensitivities.

Animals↗
PubMed2003

(18)O isotope exchange measurements reveal that calcium is involved in the binding of one substrate-water molecule to the oxygen-evolving complex in photosystem II.

Direct evidence is presented to show that calcium is inherently involved in the binding of one of the two substrate-water molecules to the oxygen-evolving complex in photosystem II. Previous rapid (millisecond range) (18)O isotope exchange measurements between added H(2)(18)O and the photogenerated O(2) have shown that the two substrate-water molecules bind to separate sites throughout the S-state cycle, as revealed by their kinetically distinct rates of (18)O exchange [Hillier, W., and Wydrzynski, T. (2000) Biochemistry 39, 4399-4405]. Upon extraction of the functionally bound calcium using a either a low-pH/citrate treatment or a NaCl/A23187/EGTA treatment and subsequent reconstitution of activity with strontium, we show for the first time a specific increase in the slow rate of (18)O exchange by a factor of 3-4. This increase in the slow rate of exchange is consistently observed across the S(1), S(2), and S(3) states. In contrast, the fast phase of (18)O exchange in the S(3) state appears to be affected little upon strontium reconstitution, while the fast phases of exchange in the S(1) and S(2) states remain largely unresolvable, at the detectable limits of the current techniques. The results are discussed in terms of a possible substrate bridging structure between the functional calcium and a catalytic manganese ion that gives rise to the slowly exchanging component.

Binding Sites↗
PubMed1979

[Evaluation of intestinal absorption of calcium by means of double-isotope methods and oral administration of the tracer].

The percent intestinal absorption of calcium was measured in normal volunteers and in patients with idiopathic hypercalciuria employing the deconvolution method, the ratio of the two administered isotopes at equilibrium and the percent of dose present in plasma 2 hr after oral administration of the tracer. Comparison of results obtained showed that the technique based on the ratio between the two radioisotopes overestimates intestinal absorption by about 9% with respect to values calculated with the deconvolution method, but gives results comparable to those determined by oral administration of the isotope. The percent dose of the tracer 2 h after i.v. administration is closely correlated with the size of the miscible calcium pool. A less significant correlation exists between the size of the pool and percent of the dose 2 h after oral administration.

Administration, Oral↗
PubMed2000

Radiochemical analysis of 41Ca and 45Ca.

The radioactive isotopes of calcium, 41Ca (t1/2 = 1.03 x 10(5) yr) and 45Ca (t1/2 = 163 d), are produced by neutron capture in the stable isotopes 40Ca and 44Ca, respectively. These radionuclides are present in the environment due to the reactions between the galactic cosmic rays and the earth's surface, and in nuclear power plants by the activation of the structural components of nuclear reactor vessels. The aim of this paper is to propose a radiochemical separation method of 41Ca and 45Ca from the other beta gamma emitters present in radioactive materials, based on selective precipitation reactions. The activities were measured by liquid scintillation counting (LSC). The obtained decontamination factors are satisfactory for each radioactive component of the initial sample in that their activities in the final product were lower than the minimum detectable activity (MDA) due to the effectiveness of the radiochemical procedure. The sensitivity of the method allows the radiological characterization of 41Ca and 45Ca content in radioactive materials.

Beta Particles↗