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PubMed1964

MORPHOGENESIS.

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Amphibians↗
PubMed1964

THE EFFLUX OF SUBSTANCES FROM FROG VENTRICLES TO SUCROSE AND TO RINGER'S SOLUTIONS.

The frog ventricle in sucrose solution contracts for several hours at 25 degrees C, and for as long as 24 hours at 5 degrees G. The possibility that a fraction of the extracellular fluid remains outside of the excitable membrane was examined by measuring the efflux of tracers. The half-time for the efflux to sucrose solution at 25 degrees C of C(14) sucrose is about 1 minute, for Na(24) is 6.5 minutes, and for Cl(86) is 4 minutes. There is no evidence for the retention of an extracellular Na fraction. The Q(10) for Na and Cl efflux is about 1.3. The half-time for K(42) efflux is about 180 minutes; the Q(10) is 1.7. The efflux rates of Na(24), Cl(36) and K(42) to sucrose and to Ringer's solutions are quite similar. Ca(45) efflux is only one-fifth as fast to sucrose solution as to Ringer's; the retention of Ca(++) may be important for maintaining excitability in sucrose solution. P(32) efflux is five times faster to sucrose solution than to Ringer's solution, and there is a similar increase in the rate of inosine loss to sucrose solution. The Q(10) for efflux to sucrose solution is 2.2 for P(32)O(4) and 2.4 for inosine. We suggest that energy metabolism is abnormal in ventricles in sucrose solution and that low temperature prolongs excitability by slowing the metabolic change.

Amino Acids↗
PubMed1991

Isotopic exchange of ingested calcium between labeled sources. Evidence that ingested calcium does not form a common absorptive pool.

We studied the extent of salt dissociation during absorption of calcium from sources of differing absorbability by measuring fractional absorption from loads in the range of 200-300 mg in healthy adult women. Sources were labeled both intrinsically and extrinsically with 45Ca and 47Ca, respectively, and were fed alone and in combination with one another. We first confirmed our previous observation of superior absorbability of calcium oxalate over spinach calcium in a randomized cross-over design in 20 women. Spinach calcium exhibited only half the absorbability of the same load of calcium presented as the oxalate. Then, in 14 women fed spinach with both an intrinsic and an extrinsic label, apparent absorption of the extrinsic label averaged 0.130 +/- 0.041 and of the intrinsic label, 0.029 +/- 0.023. Thus, the extrinsic tag was partially, but not completely, bound by the spinach. In the same 14 women, milk absorption averaged 0.331 +/- 0.092 when ingested alone. However, when co-ingested with spinach, apparent milk calcium absorption fell to 0.267 +/- 0.079 and apparent spinach calcium absorption rose to 0.111 +/- 0.039. Thus, there was significant but incomplete label exchange between the two sources, indicating that at least some of the calcium from both sources enters a common preabsorptive, ionic pool. By contrast, we had previously shown no tracer exchange when labeled oxalate was co-fed with labeled milk. We conclude that (1) the presence of calcium as the oxalate in spinach is not a sufficient explanation for the poor absorbability of spinach calcium; and (2) oxalate calcium and spinach calcium are absorbed by different mechanisms, one involving a common preabsorptive pool and the other not.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗
PubMed1993

Calcium absorption and metabolism in children with juvenile rheumatoid arthritis assessed using stable isotopes.

OBJECTIVE: To assess calcium intake, absorption, urinary excretion and the fraction of urinary calcium originating from bone and diet in patients with juvenile rheumatoid arthritis (JRA). METHODS: A dual tracer stable isotope technique was used to study 6 girls and 3 boys with JRA. RESULTS: Fractional absorption in the 6 girls, ages 4-9, with JRA was significantly lower than that in 10 similar, healthy girls (22.6 +/- 4.7% vs 30.4 +/- 8.4%, p = 0.033). Urinary calcium excretion tended to be higher in the girls with JRA than in controls, (2.9 +/- 1.5 vs 1.6 +/- 1.7, p = 0.15). The urinary calcium in patients with JRA was derived principally from bone, and there was no increase in diet derived urinary calcium. One of the boys with new onset JRA was markedly hypercalciuric and in negative calcium balance (-222 mg/day). CONCLUSION: Our data show that hypercalciuria in patients with JRA results from bone resorption, not hyperabsorption of dietary calcium and suggest that increases in calcium intake may benefit children with JRA.

Adolescent↗
PubMed1972

The efflux of calcium from single crab and barnacle muscle fibres.

1. The efflux of calcium, as the isotope (45)Ca, has been investigated from single muscle fibres from the barnacle Balanus nubilus and from the crab Maia squinado.2. If the isotope was initially injected with sufficient calcium (5-65 mM) to cause a contraction, the efflux did not follow first order kinetics. There was an early rapid phase which reached a peak after 5-10 min and then declined slowly over a period of 50-150 min to a low residual value.3. Injection of the isotope with the calcium-binding agent EGTA, so that the injected free calcium concentration was ca. 2 x 10(-8)M, abolished the initial rapid loss of calcium. The efflux rose to give a steady value after 10-15 min and its magnitude was similar to the value of the residual efflux.4. The rate constant for the low residual loss was ca. 7 x 10(-4) min(-1) for Maia and ca. 17 x 10(-4) min(-1) for Balanus. The rate constant predicted a calcium efflux of 0.4 p-mole/cm(2).sec for Maia and 1-2 p-mole/cm(2).sec for Balanus at 16-25 degrees C based on the total fibre calcium concentration.5. The residual calcium efflux was not affected by 0.5 mM ouabain or 0 potassium salines applied externally. It was stimulated, some 10-15 times in Maia and to a lesser extent in Balanus, by salines containing 600 mM potassium or 2-5 mM caffeine. The increased efflux was associated with a brisk contraction.6. External application of salines containing 20, 40 or 60 mM potassium or 0.5 mM caffeine in Maia produced some stimulation of the residual efflux but no visible contraction.7. Pre-treatment of Maia fibres with 40 mM potassium or 0.5 mM caffeine salines abolished the ability of the fibres to respond to higher concentrations of these agents. A depletion of a releasable calcium fraction by these subthreshold stimuli could explain this phenomenon.8. Electrical stimulation, the injection of 50 mM calcium chloride or 50 mM caffeine produced an elevated calcium efflux which was associated with a contraction.9. Intracellular injections of EGTA only lowered the residual efflux by up to half its initial value. This suggests that calcium can be released rapidly within these muscle fibres and that the sarcoplasmic calcium concentration is not much altered from its normal value by the injection.10. The experiments suggest that in Maia, changes in the calcium efflux reflect in magnitude, but not in time course, the internal calcium changes which can be observed with the calcium-sensitive protein, aequorin.

Action Potentials↗
PubMed1985

Absorption of calcium in premature infants as measured with a stable isotope 46Ca extrinsic tag.

Absorption of dietary calcium was evaluated with the extrinsic tag approach and stable isotope methodology in growing premature infants. Fractional absorption of a bolus dose of 46Ca was determined on 16 occasions in 13 premature infants (birth weight 1135 +/- 40 g, gestational age 29.5 +/- 0.4 wk, mean +/- SE) and was found to be 84.4 +/- 2.2%. Fractional absorption of 46Ca ranged between 65 and 97%, and did not appear to be influenced by postnatal age, postconceptual age, body weight, or intake of preterm human milk, fortified preterm human milk, or premature formula. Therefore, if absorption of the 46Ca dose reflects that of dietary calcium, about 80% of dietary calcium is absorbed.

Absorption↗
PubMed2005

Dietary inulin intake and age can significantly affect intestinal absorption of calcium and magnesium in rats: a stable isotope approach.

BACKGROUND: previous studies have shown that non-digestible inulin-type fructan intake can increase intestinal mineral absorption in both humans and animals. However, this stimulatory effect on intestinal absorption may depend on experimental conditions such as duration of fermentable fiber intake, mineral diet levels and animals' physiological status, in particular their age. OBJECTIVES: the aim of this study was to determine the effect of inulin intake on Ca and Mg absorption in rats at different age stages. METHODS: eighty male Wistar rats of four different ages (2, 5, 10 and 20 months) were randomized into either a control group or a group receiving 3.75% inulin in their diet for 4 days and then 7.5% inulin for three weeks. The animals were fed fresh food and water ad libitum for the duration of the experiment. Intestinal absorption of Ca and Mg was determined by fecal monitoring using stable isotopic tracers. Ca and Mg status was also assessed. RESULTS: absorption of Ca and Mg was significantly lower in the aged rats (10 and 20 mo) than in the young and adult rat groups. As expected, inulin intake increased Ca and Mg absorption in all four rat groups. However, inulin had a numerically greater effect on Ca absorption in aged rats than in younger rats whereas its effect on Mg absorption remained similar across all four rat age groups. CONCLUSION: the extent of the stimulatory effect of inulin on absorption of Ca may differ according to animal ages. Further studies are required to explore this effect over longer inulin intake periods, and to confirm these results in humans.

Aging↗
PubMed1998

Insights into bone metabolism from calcium kinetic studies in children.

Changes in the mineralization rate of the skeleton during childhood are related to normal growth and pubertal development. These may be affected by genetic factors, including race and gender, and by the presence of abnormalities of growth or hormonal abnormalities such as occur in children with chronic illnesses. We have used multicompartmental studies to examine calcium kinetics in healthy children ranging in age from premature infants of 1-2 kg body weight through adolescence. These studies are performed using orally and intravenously administered stable isotopes of calcium. Sample collection requires multiple blood samples to be obtained during the initial time period after isotope dosing, which is feasible in older children using an indwelling catheter. We have found that the peak rate for both bone calcium deposition and removal occurs in girls during the year before menarche. Peak kinetic rates decrease in an exponential fashion post-menarche. On a body-weight basis, the greatest rates of bone calcium deposition and removal are in infants, especially premature infants.

Administration, Oral↗
PubMed1994

Pathophysiology of hypocalciuria in preeclampsia: measurement of intestinal calcium absorption.

OBJECTIVE: To analyze calcium absorption using stable isotopes in patients with preeclampsia and in normotensive controls. METHODS: Fifteen pregnant subjects were studied: eight with preeclampsia (hypertension and proteinuria) and seven normotensive controls. All patients were ingesting their normal diet. The subjects received two stable calcium isotopic tracers. An oral tracer (44Ca, 0.0124 mmol/kg) was given with milk, while an intravenous tracer (42Ca, 0.00249 mmol/kg) was infused over 7-10 minutes. Calcium concentration was determined by atomic absorption spectrophotometry, and isotope ratios by thermal ionization mass spectrometry from pooled 24-hour urine samples. RESULTS: No difference was noted in fractional intestinal absorption between preeclamptic subjects (0.282 +/- 0.051) and normotensive controls (0.306 +/- 0.079) (P = .49). However, the fraction of dietary calcium appearing in the urine differed significantly (0.06 for preeclamptic subjects and 0.087 for normotensive controls; P = .008). CONCLUSIONS: Despite the indirect evidence of others, calcium absorption does not appear to be impaired in patients with preeclampsia. The retention site of the unexcreted calcium is unidentified.

Adult↗
PubMed2004

Calcium kinetics are altered in clinically stable girls with cystic fibrosis.

Reduced bone mass in individuals with cystic fibrosis (CF) may result from alterations in calcium metabolism. Bone calcium deposition and resorption rates, calcium balance, and markers of bone turnover were assessed using stable isotopes of calcium in 22 prepubertal and pubertal girls with CF. Bone calcium deposition was associated with the availability of dietary calcium, total serum osteocalcin, and leptin concentrations. Reduced bone mass in individuals with CF may result from inadequate bone calcium (Ca) deposition, and excessive resorption, although these parameters have not been directly assessed in children with CF. We used stable Ca isotopes to measure rates of bone Ca deposition (Vo+), resorption, and retention in 22 clinically stable girls with CF (aged 7-18 yr). Rates of bone Ca deposition were determined by mathematically modeling the disappearance of iv Ca stable isotope ((42)Ca) for 6 d post dosing. Indirect markers of bone turnover and hormones associated with pubertal development were also assessed. Rates of bone Ca deposition and retention were highest during early puberty (Tanner stages 2 and 3). Calcium deposition rates in prepubertal (Tanner 1) and postmenarchal girls (Tanner stages 4 and 5) did not support substantial bone Ca retention. Net absorption of dietary Ca and serum osteocalcin and leptin concentrations were positively associated with Vo+. Time post menarche and serum leptin concentrations explained 91% of the variability in Vo+ (P = 0.0007). Serum total osteocalcin was low (10.9 +/- 5.4 ng/ml), and a substantial percentage of osteocalcin was undercarboxylated (54.3 +/- 11.8%). We concluded that increased calcium absorption and serum leptin concentrations were significantly associated with rates of bone Ca deposition, demonstrating an impact of nutritional status on this process. Rates of bone Ca deposition were lower than typically reported in healthy children, as were indirect markers of bone formation. These alterations in bone turnover contribute to reduced bone mass in girls with CF.

Absorption↗