Concentration Of 45Ca Research Articles

Effects of cytochalasin B and dihydrocytochalasin B on calcium transport by intestinal absorptive cells.

In vivo calcium absorption was studied in normal and rachitic chicks. Cytochalasin B (CB) at a concentration of 25 microgram/ml added to the medium inside the duodenal lumen inhibited calcium absorption (20 min) from 82.5 +/- 1.9% of calcium absorbed in the controls to 59.2 +/- 3% in normal and from 70.0 +/- 2.3% to 47.0 +/- 2.1% in rachitic chicks. In vitro studies by everted ileal sacs of young rabbits also showed an inhibition of active transport of calcium due to CB. Whereas in the controls the ratio of 45Ca concentrations in serosal and mucosal media (60 min) was 7.2 +/- 0.32, the ratios were 5.24 +/- 0.52; 4.40 +/- 0.36; 3.40 +/- 0.42; 5.77 +/- 0.52; 1.38 +/- 0.08; and 1.06 +/- 0.02 in the presence of CB at concentrations of 5, 10 and 25 microgram/ml; colchicine 10(-4)M, Na citrate 0.02M, and heat-devitalized conditions, respectively. 45Ca concentration in the mucosal scrapings was also affected. It showed an increase from controls (15,101 +/- 404 cpm/mg) and correlated with CB concentration: 17,378 +/- 489, 19,015 +/- 1000, and 20,201 +/- 362 at 5, 10, and 25 microgram/ml, respectively. Dihydrocytochalasin B also inhibited active calcium transport and caused an increase in 45Ca concentration in the mucosal scrapings. Correlated electron microscopic studies showed certain changes in the brush border, especially in some actin microfilaments in the terminal web region. It seems that these morphological alterations may be related to transcytoplasmic movement of calcium.

Effects of CO2, acetylcholine and caerulein in 45Ca efflux from isolated mouse pancreatic fragments.

Mouse pancreatic fragments were loaded with45Ca and placed in a flow cell. The concentration of45Ca in the effluent was measured. The effects of changing the tension of carbon dioxide on45Ca efflux were observed and compared with effects of pancreatic secretagogues.

Uptake in vivo of 45Ca in male accessory sex organs of the rat: Effect of estramustine phosphate and diethylstilbestrol diphosphate

The radioactivity following a single i.v. injection of 45Ca into male rats was found to be significantly higher in seminal vesicles, dorsolateral prostate, coagulating glands and ventral prostate than in muscle. The acute effect of a single dose given intraperitoneally of estramustine phosphate (Estracyt ®) and diethylstilbestrol diphosphate (Honvan ®) were examined on 45Ca uptake. Generally, the 45Ca concentration in the accessory sex organs with the exception of the dorsolateral prostate increased after administration of estramustine phosphate. Diethylstilbestrol phosphate treatment also significantly increased 45Ca uptake in the ventral prostate when measured on the basis of tissue wet weight but not on the basis of protein. The implications of these findings are discussed in relation to the therapeutic action of Estracyt in prostatic carcinoma.

Endogenous nature of circadian rhythms in calcium metabolism.

Rats studied when the lights are on from 0600 to 1800 daily and fed only in the dark period displayed circadian rhythms in plasma calcium (ionized and total) and 45Ca concentrations, 6 and 8 days after 45Ca administration. In rats fed a calcium-deficient diet, the amplitude of daily variation of plasma ionized and total calcium increased markedly whereas plasma 45Ca daily fluctuation remained essentially unchanged. In the calcium-deficient rats, significant correlations between plasma calcium and 45Ca and between plasma calcium and magnesium were observed throughout the 24 h; circadian periodicity of calcium metabolism persisted in rats fasted overnight, regardless of the illumination schedule. Normal daily fluctuations in plasma 45Ca, lost after thyroparathyroidectomy (TPTX), were restored by feeding the TPTX rats a high-calcium diet. These results demonstrate clearly that circadian rhythms of calcium metabolism occurred irrespective of the light-dark schedule, the calcium supply through intestines and the thyroparathyroid system. An attractive suggestion is that circadian rhythmicity originates as a result of dynamic properties involving nonlinear processes of calcium metabolism.

Accumulation and localization of radiocalcium in the rat thyroid gland.

To determine the rate of accumulation of radiocalcium (45Ca) in the thyroid gland, the concentration of radiocalcium was measured in the blood serum and thyroid gland at various time intervals up to 7 days after a single ip injection of 45Ca in rats. The ratio of the 45Ca concentration in thyroid gland to serum (T:S) increased with the time interval after injection. Thyroid activity was varied by hypophysectomy or by feeding a low iodine diet with or without added thiouracil. The more active the gland, the faster it equilibrated with the serum 45Ca and the less was the T:S in the steady state. The equilibration was much slower than for radioiodide, taking several days in normal control rats and hours in very active glands. Autoradiographs showed that the 45Ca concentration was higher in association with the follicular epithelium than with the follicular lumen at 1 h or less after injection. However, at 24 h, the concentration of 45Ca was higher in the lumen than elsewhere in the gland. To determine rate constants describing the equilibration, the data in the normal gland were fitted with a model that took account of the differing rates of equilibration in cell and lumen. The presence of calcium in the lumen indicates that each time the follicular epithelial cell endocytosed stored luminal colloid before secretion, it also took in an appreciable amount of calcium.

An interpretation of acute changes in plasma 45Ca following parathyroid hormone administration to thyroparathyroidectomized rats.

Acute changes in plasma calcium and 45Ca were studies in young adult male thyroparathyroidectomized (TPTX) rats injected with moderate doses of parathyroid hormone (PTH). For plasma calcium changes, comparison was made between rats fasted or fed prior to PTH injection. For plasma 45Ca changes, the effect of the time of administration of the radionuclide was also studied; this included rats injected with PTH 1 h after radionuclide ("1 h 45Ca"), 18 h later ("18 h 45Ca") and more than 6 days later ("6 day 45Ca"). The results can be summarized as follows: (1) Plasma calcium changes were greater when PTH was injected into "fed" rather than into "fasted" rats. (2) PTH always produced a relative increase (compared to controls tested concurrently) in plasma 45Ca concentrations. This increase was the same in the "1 h 45Ca" and the "18 h 45Ca" group. (3) Plasma 45Ca rose at least temporarily following PTH injection in the "18 h 45Ca" group. (4) The 45Ca rise following PTH was always greater in "fed" than in "fasted" groups. (5) Plasma 45Ca specific activities (S.A.) tended to rise in the "6 day 45Ca" group and to fall in the "18 h 45Ca" group, following PTH injection. However, the 45Ca S.A. was always higher in fed than fasted groups. (6) In a few experiments in which 32P was injected with 45Ca, specific activity changes in plasma 45Ca following PTH injection were not accompanied by similar changes in 32P specific activity. These results could not be adequately explained by PTH effects on bone resorption, but the data supported the postulate that PTH controls plasma calcium concentrations by increasing transport of calcium through the osteocyte-lining cell (osteoblast) bone cell complex from the bone fluid compartment to the ECF.

Calcitonin and the Bone Fluid Compartment

Changes in plasma calcium and 45Ca concentrations were followed after injection of calcitonin or a combination of calcitonin (CT) and parathyroid hormone (PTH) into thyroparathyroidectomized rats maintained on thyroxine. Comparison was made between rats injected with the hormone(s) after a recent feeding and after an overnight fast. Also cor (18 hr 45Ca) before, and more than 6 days (greater than 6 day 45Ca) prior to hormone administration. The following results were obtained: The action of CT predominated over that of PTH for the first few hours after injection. However, the effects of PTH were eventually manifested even when additional CT was administered. In the "greater than 6 day" 45Ca groups, PTH normally produced an increase in plasma 45Ca specific activity. However, in fasted rats, plasms 45Ca fell with total calcium with no change in specific activity following CT injection. In fed rats CT injection was followed by a decrease in plasma 45Ca specific activity. When both hormones were administered plasma 45Ca specific activity changes mimicked those produced by CT alone even after PTH plasma effects were manifested. In the "18 hr" 45Ca groups, CT produced first a drop in plasma 45Ca, followed by a reduction in the rate of its removal from plasma. It is concluded that the data can best be explained by the postulate that plasma calcium concentrations are maintained by the control of fluxes between bone fluid in the osteocyte-lining cell bone unit and the extracellular fluid. PTH increases the efflux from this bone fluid compartment while CT restricuts the source of calcium and, therefore, the efflux. Plasma 45Ca changes are due to a combination of changes in flux rates and mixing processes between the extracellular fluid compartment and the bone fluid compartment.

Relationship of blood concentrations of calcium, phosphate, gastrin and calcitonin to the onset of feeding in the rat.

Daily fluctuations in plasma calcium concentrations in rats trained to a closely regulated feeding pattern have been compared to corresponding plasma gastrin and calcitonin concentrations. The time period studied was that extending from 4 hr prior to the start of the feeding. Both plasma calcium and phosphate levels fedd prior to the start of the feeding period and remained low at least for the first 2 hr of feeding. This pattern was also observed in rats in which food was withheld for 2 hr past the regular feeding time. Plasma 45Ca and 32P concentrations (radionuclide injected at least one week prior to sampling) did not follow the pattern of their stable counterparts. Instead, these values rose or remained constant until after feeding had commenced, after which they fell precipitously. Both plasma calcitonin and gastrin levels rose rapidly after the start of the feeding period. The primary point of emphasis is that calcitonin secretion was produced in these rats by an intestinal related stimulus and not by a rise in plasma calcium concentration.

Evidence for the role of calcium ions and mitochondria in the maintainance of anaesthesia in the rat

Alphaxalone, the major component of the steroid anaesthetic, Althesin, inhibited the uptake of 45Ca 2+ into mitochondria isolated from rat brain. The subcellular distribution of calcium in the brain was measured after intraperitoneal injection of 45Ca 2+. The concentration of 45Ca 2+ in the brain reached a maximum after 3min, the greatest concentration being found in the mitochondrial fraction. Pre-treatment of rats with Althesin, hexobarbitone or halothane reduced the accumulation of 45Ca 2+ by brain mitochondrial fractions. The possible involvment of calcium ions in the mechanism of action of general anaesthetics is discussed.

Effect of fasting and parathyroid hormone injection on plasma 45Ca concentrations in rats.

Young male rats were administered 45Ca 5 days to 2 weeks prior to use. All rats were either parathyroidectomized (PTX) or thyroparathyroidectomized (TPTX) and given several days to recover from surgery. The first group of rats were maintained on a 12 h dark-fed and 12 h light-fasted daily cycle. The remainder of the rats were used for parathyroid hormone (PTH) studies (0.1-0.6U/g body weight) following which blood samples were obtained from the tail for 1 to 6 h. Two groups of these rats were bilaterally nephrectomized 18 h before PTH injection. Two contrasting results were obtained: in PTX (or TPTX) rats maintained on the closely regulated food and light regime, plasma 45Ca concentrations rose markedly each day at the start of the fasting period and then fell slowly. Total plasma calcium values fell throughout the fasting period. A similar rise and fall was also observed in 45Ca values of rats experimentally fasted after being maintained with food continuously available. In contrast, in all PTX or TPTX rats, PTH injections was followed by an equal rise in both plasma calcium and 45Ca values so that for the first few hours plasma 45Ca specific acitvity was unchanged. These data are consistent with the concept of a bone fluid compartment (BFC) separated by a cellular interface from the primary extracellular fluid space (ecf). It is postulated that through this cellular interface calcium is actively "pumped" from the BFC to the ECF. The rise in plasma 45Ca values at the start of fasting is explained on the basis of decreased entry of stable calcium from the gastrointestinal tract and a continued movement of calcium and 45Ca from the BFC to the ECF. The concomitant increase in plasma calcium and 45Ca during the first few hours after PTH injection is explained by a rapid action of PTH to increase the rate of calcium movement from BFC to ECF by its action at the cellular interface, without altering 45Ca specific activity until such time as dissolution of bone crystals is required as a supply of calcium.

Effects of long-term administration of bendroflumethiazide on bone metabolism in the rat.

Abstract: 45Ca was injected subcutaneously in 160 g rats kept in metabolic cages. After an adjustment period of 10 days, bendroflumethiazide was given orally for another 10 days. The concentration of 45Ca and the specific activity in the bones was significantly higher in the thiazide treated animals than in controls. The excretion of hydroxyproline decreased slowly during the thiazide administration period. The results suggest that the breakdown of both bone mineral and bone matrix was reduced during bendroflumethiazide administration. Bone matrix metabolism was not normalized until 7 days after cessation of thiazide administration as judged by the time required for reversion of the hydroxyproline excretion.

Mechanism of the hypocalcaemic action of parenterally administered magnesium.

ABSTRACT Subcutaneous injection of 300 μmol magnesium raised the serum magnesium to 4.00 mmol/l after 30 min in 150 g male rats and reduced the serum calcium concentration by 0.17 mmol/l after 60 min. Magnesium also acutely diminished the serum concentration of 45Ca given three weeks previously. The administration of magnesium did not reduce the serum concentration of 45Ca and did not increase the rate of disappearance of 45Ca from the serum, when subcutaneous or intravenous labelling took place 180–210 min before the magnesium injection. The magnesium-induced hypocalcaemia therefore cannot be explained by an increased removal of calcium from the circulation. The results are compatible with the hypothesis that the magnesium-induced hypocalcaemia is caused by the release of calcitonin. Injections of 300 μmol magnesium chloride at 12 h intervals for 72 h trebled the 24 h renal excretion of both 40Ca and 45Ca given three weeks previously. The 24 h renal excretion of hydroxyproline was unaltered. Thus there was no indication that the intermittent magnesium injections produced any long-term inhibition of the turnover of bone matrix and bone mineral.

Effect of recent red leaf virus infection on the distribution of 65Zn, 45Ca, and 54Mn in subterranean clover

Subterranean clover (Trifolium subterraneurn L. cv. Yarloop) was grown in nutrient solutions which were supplied with 45Ca, 65Zn, or 54Mn either before (series A) or at the same time as (series B) the plants \+ere inoculated with subterranean clover red leaf virus (SCRLV) by means of the aphid vector Acyrthosiphon solani Kltb. SCRLV infection affected the distribution of each isotope, but less in series A than in series B plants. In both series, movement of the isotopes from the petiole (P) into the lamina (L) was retarded. In series B this resulted in a significant decrease in the concentration of 45Ca, 65Zn, or 54Mn in the lamina. The L/P ratios of concentration and the total contents of 65Zn and 54Mn in the leaves of SCRLV-infected plants from both series were also reduced. In addition SCRLV infection reduced the 54Mn concentration in the distal third more than in the remainder of the lamina. SCRLV infection increased the dry weight of the lamina and/or the LIP ratio of dry weight of the younger leaves of the series B plants.

Mid-season movement of 45Ca in apple trees

Apple trees (cv. Granny Smith) were grown in sand or water cultures supplied with a complete nutrient solution. 45Ca added to this solution c. 11–14 weeks after full bloom became distributed throughout each tree. It moved preferentially into the interveinal tissues of the young rather than the old leaves of the terminal growth. The 45Ca concentration was highest in the petiole, midrib, and veins and comparable for both types of leaf in these tissues. In the tree trunk, leaders, and fruit spurs the 45Ca concentration was much higher in the bark than in the wood. Although the isotope entered the bark and leaves of the fruit spurs it was not detected in the flesh of the attached fruits. It occurred in low concentration in the pedicels of a few fruits. When supplied to trees 4–5 weeks after full bloom, 45Ca did enter the fruits, but its concentration was much less than in the bark of the fruit spurs. In such fruit the concentration of 45Ca was highest in the core towards the stem end, least in the flesh, and intermediate in the peel.

Parathyroid hormone and thyrocalcitonin function in adrenalectomized rats.

The effect of adrenalectomy on the ability of the parathyroids or appropriate cells in the thyroid in the rat to respond to low or high calcium challenge was studied. Using 200 g male rats the following experimental groups were included: controls, parathyroidectomized (PTX), adrenalectomized (ADX), parathyroidectomized- adrenalectomized concurrently, parathyroidectomized 5 days after adrenalectomy, thyroidectomized (TX) and thyroidectomizedadrenalectomized concurrently. High calcium challenge was administered by intraperitoneal injection of 5 mg Ca/100 g body wt in 2 injections. The following results were noted: 1) Adrenalectomy alone had little or no effect on plasma calcium and phosphate levels under the conditions of these experiments, though it decreased urinary excretion of phosphate and increased by 30% the plasma concentration of 45Ca administered 2 weeks prior to the experimental studies. 2) Parathyroidectomy in adrenalectomized rats differed from that in adrenal-intact rats in that the rate of fa...

Distribution of orally administered 45Ca in rat intestinal tissues and vitamin D3 effect.

The effects of vitamin D3 and actinomycin D on the radioactive calcium distribution were studied in the rat intestinal mucosa and muscle 5 and 30 minutes after the oral administration of 45Ca.1. Serum 45Ca concentration at 30 min was increased significantly in the vitamin D3 treated rat, and this vitamin D3 effect was inhibited by actinomycin D. The action of vitamin D3 and actinomycin D was not observed at 5 min. 2. 45Ca was observed in the proximal parts of intestinal mucosa (from pyloric end to 30cm) at 5 min, and at 30 min it came to be observed in the distal (40-60cm). 45Ca in the proximal parts at 5 min was reduced with vitamin D3, and actinomycin D did not seem to be influenced on this vitamin D3 action. 45Ca in the distal (at 30 min) was enhanced with vitamin D3 and this action was partially inhibited by actinomycin D. 3. 45Ca in muscle was lower than in mucosa. Observed pattern of 45Ca distribution at 5 min in muscle was not so different in vitamin D deficient and D3 treated rats. Actinomycin D did not exert its action on muscle at 5 min. Distribution patterns of 45Ca in muscle at 30 min were almost similar to the mucosal patterns. 4. Subcellular distribution of 45Ca was observed in the duodenal mucosa. Nuclei and cell debris (brush borders) have relative amounts of 45Ca 5 min after 45Ca administration. At 30 minutes, 45Ca of subcellular fraction was significantly decreased, especially in nuclei, cell debris and mitochondria. This reduction was moderated by vitamin D3. Actinomycin D inhibited this vitamin D3 action in microsomes and supernatants.From these results, it was suggested that calcium transport would be carried out in two ways, membrane permeable system (actinomycin D insensitive) and the system involving calcium carrier protein (actinomycin D sensitive).

Calcium accumulation by isolated nerve ending particles from brain. II. Factors influencing calcium movements.

AbstractA synaptosomal preparation from rat brain accumulated 45Ca by a temperature‐sensitive process requiring ATPd̊ and Mg++. The uptake of 45Ca was correlated with a net increase in total calcium, and after brief incubations the concentration of 45Ca in the particles was several hundred times that remaining in the medium. Calcium accumulation was associated with a corresponding stoichiometric accumulation of phosphate. Synaptosomes that had accumulated 45Ca during a prior incubation lost the radioactivity during a subsequent incubation in the absence of ATP. NaCl increased the efflux of accumulated 45Ca, a process distinguishable from the non‐specific inhibition of 45Ca accumulation by various solutes corresponding with their effects on intra‐synaptosomal volume. The Na+‐induced efflux of 45Ca was not affected by ouabain. Since the intrasynaptosomal mitochondria have been identified as the site of 45Ca accumulation in synaptosomes, the data suggest that these mitochondria may function as reservoirs of releasable Ca++ within the nerve ending, possibly participating in the Ca++‐dependent process of neurotransmitter release.

Enhanced permeability to sugar associated with muscle contraction. Studies of the role of Ca++.

When contractures were induced in isolated frog sartorius muscles with 4 mM caffeine, there was an increase in permeability of the muscle cells to 3-methylglucose. This observation suggests that the changes in permeability to sugar that are known to occur in electrically stimulated muscles may not be intimately related to the depolarization phase of the tissue response. Contractures that were elicited by exposing the muscles to a high concentration of K+ were also associated with an increased permeability to sugar. As the concentration of 45Ca in the medium was raised, more 45Ca entered the muscles during potassium contractures, and the contractures lasted longer, in agreement with the observations of other investigators. There was also a greater change in permeability to sugar when potassium contractures were elicited in the presence of higher concentrations of Ca++. The possibility that the enhanced permeability to sugar may be related to changes in the intracellular concentration of Ca++ is discussed.

Placental Transfer and Fetal Utilization of Calcium in Developing Swine

Radioisotopic chemical balance and tissue distribution studies were used to investigate the source and fetal-maternal behavior of retained calcium in 38 gilts as a function of gestation age and of time after administration of radioactive calcium. Sows killed during the first, second and third trimester, following oral or intravenous dosing with 45Ca showed no significant effects of pregnancy on maternal absorption, plasma 45Ca or tissue calcium concentration. At 35, 70, 105 and 114 days' gestation, 0.9, 60, 17.8 and 21.3%, respectively, of the absorbed 45Ca was transferred to litters standardized to 8 pigs, whereas less than one per cent was retained in the combined placenta and fluids after 168 hours. Fetal bone calcium values, reflecting degree of mineralization, increased rapidly between trimesters 1 and 2, with less change to parturition. Tissue distribution patterns for retained 45Ca paralleled those for the dam, but utilization rate and fetal specific activity values were greater. Fetus-to-dam concentration and fetal specific activity ratios were higher for bone than soft tissue, and decreased generally with gestation age and with time after dosing. Utilization efficiency of absorbed maternal calcium for fetal development increased as pregnancy advanced, reaching 21.3% of the 45Ca dose at 114 days' gestation.

軟体動物石灰化組織の鉱物化に関する研究-III

1) The localization of 45Ca in the mantle and on inner shell surface was determined for several marine molluscs with radioautographic stripping film, and discussed calcification of shell in special reference to mineralization and crystalline structure of shell. 2) Specific and local differences of calcium deposition revealed in amount and mode on the inner surface of a shell of experimental specimens and whereby specific patterns might result. 3) Specific pattern suggested the mode of development and formation of shell, while local pattern took place in close connection with crystalline structure in the corresponding areas and appeared to be characterized depending on tension and elongation of mantle tissue. 4) High concentration of 45Ca was localized in epithelium and sub-epithelium of mantle. 5) The presence of 45Ca was detected in mucus excreted through outer epithelium. 6) In all specimens, muscle impressions indicated the smallest amount of calcium deposition in a whole surface of a shell.