Radioactive calcium

Pecher, C. 1941 Biological investigations with radioactive calcium and strontium. Proceedings of the Society for Experimental Biology Medicine 46 86-91. 

From the earliest measurements of tissue calcium, it was clear that total calcium is largely a measure of stored calcium. Through the years, scientists have used a variety of indirect measures of [Ca2+]j. These include shortening of or tension in muscles secretion from secretory cells the activity of Ca2+-dependent enzymes, most notably glycogen phosphorylase and flux of K+, or K+ currents, as a reflection of Ca2+-activated K+ channels. In addition, investigators often use the radioactive calcium ion [45Ca2+] as an indirect indicator of Ca2+ concentrations and Ca2+ movements. 

The level of ionized calcium is calculated from the measured residual, radioactive calcium and the stability constant of Ca EGTA =... 

The amount of calcium deposited tit bone at any moment may be determined from experiments with radioactive calcium. In grow ing individuals, it exceeds the amount removed by bone destruction. In adults, it is about the same as the amount removed. Such individuals arc considered to be in "zero" calcium balance. In older persons. Ihe amount deposited is less than the amount removed. 

Harrison GE, Carr TEF, Sutton A. 1967. Distribution of radioactive calcium, strontium, barium and radium following intravenous injection into a healthy man. Int J Radiat Biol 13 235-247. 

The experimental procedures have been described in detail (3,4), but are briefly described here for completeness. Chick forebrains were removed, separated at the midline, and incubated at 37°C in a physiological buffer containing radioactive calcium ions (45Ca ). Any radioactivity not tightly associated... 

Once mobilized, a large proportion of the cytosolic calcium load is extruded from the cell across the plasma membrane. This extrusion can be demonstrated by measuring the efflux of radiocalcium from previously labeled cells. All stimulation of adrenal, hepatic and vascular smooth muscle cells preloaded with radioactive calcium induces a marked increase in efflux of the radiolabel. This increased efflux is transient, peaking between 4 and 5 minutes after All addition and is observed in the absence of extracellular calcium [39]. Furthermore, under conditions of zero calcium, treatment of cells with dantrolene prior to hormonal stimulation abolishes the All-induced calcium efflux [40], confirming that the radiocalcium lost from the cell is mobilized from a component of the ER. 

The study shown in Figure 9.53 illustrates the role of 1,25-dihydroxyvitamin D3 in stimulating the uptake of calcium ions by the intestines. Chick duodena were Incubated in a salt solution containing radioactive calcium ions and vitamin D at the indicated levels Each point in the figure represents the uptake of calcium occurring during a separate incubation period. The forms of the vitamin used included 1,25-(OH)2D3 ( ), l-fOHJD (A), 25-(OH)D3 (A), 24,25-(OH)jDj (O), and... 

The double-isotope technique is carried out as follows (DeGrazia et al., 1%5). The subject eon.sumes a test food containing caldum-45. About halfway through the absorpbve process, caJcium-47 is injected into a vein, in the form of a solution of CaCb. The absorptive process is about halfway complete at about 2 hours after a meal. The injected Ca is calcium that is 100% absorbed- A urine sample is collected 1 day after the oral aiid intravenous doses of radioactive calcium. The fraction of the oral dose absorbed is calculated by the formula ... 

Calcium absorption can also be measured by determining the fracbon of the mineral in a test dose that is not absorbed. Here, a test meal containing calcium-47 is consumed and the feces collected for 12 days to measure the isotope excreted The calcium lost in biliary and intestinal secretions may be corrected for by an intravenous injechon of radioactive calcium (Spencer et al., 1978). 

The measurement of calcium absorption is of interest to those studying the availability of the calcium in various foods or supplements. The quantity and availability of food calcium are concerns in the prevention of osteoporosis. Calcium absorption is also of interest to those studying the interactions between different components of food and their influence on calcium absorption. Measurement of either fecal or urinary Ca can indicate the extent of absorption, but some fine-tuning is needed to yield an accurate picture, as described in what follows. The radioactive calcium can be supplied as calcium-45 or calcium-47. Where tire absorption of food Ca is of interest, ttie study can be run most accurately by using food containing naturally labeled calcium, that is, foods grown or animals raised in the presence of radioactive calcium. A less accurate picture can be attained by mixing radioactive calcium with the food, that is, with the plant or animal product. 

Johnston and Deiss (Jl) injected rats with °Ca a few hours before thyrocalcitonin administration. They found the expected reduction in the plasma calcium concentration, although its specific activity was higher in the thyrocalcitonin-treated group than in the controls this is consistent with an inhibition of release of unlabeled calcium from bone, but could not be explained on the basis of an increased outfiow of labeled calcium into tissue from the plasma. When tracer calcium was administered 10-14 days prior to thyrocalcitonin injection, the hormone produced a decrease in both stable and tracer calcium in the blood plasma, indicating an inhibition of calcium release from bone. In these animals having labeled bone calcium, increases in stable and radioactive plasma calcium resulted from the administration of parathyroid extract alone, although the simultaneous administration of parathyroid extract and thyrocalcitonin resulted in no net change in either stable or radioactive calcium. It was concluded that both hormones probably act on a similar metabolic compartment in bone. 

Much has been written about the favorable effects of androgenic-anabolic agents on calcium balance, for which they have been widely used. A recent report combined both calcium balance and radioactive calcium turnover studies (25). It again showed the favorable effects of the steroids, which these authors attributed to a decrease in resorption of bone. 

Alizarin is also used diagnostically as a marker for the study of bone growth. Alizarin and radioactive calcium are deposited similarly in growing bones, including those of the skull. The results that can be obtained by the use of alizarin or radioactive calcium are fully complementary. The hazard of the radioactive calcium to both the investigator and the patient does not arise from the use of alizarin [1,148]. 

Strontium is excreted in urine and, to a lesser extent, in feces, milk, and sweat. In healthy adult subjects, total clearances of 9.4-11.7 mL/min [58,59] were demonstrated, while the renal clearance appeared to vary between 4.0 and 5.4 mL/min [58,59]. Studies based on the simultaneous administration of radioactive calcium and strontium revealed that the strontium/calcium ratio is higher in urine than in the glomerular filtrate, which suggests that the two elements are discriminated during tubular reabsorption in the kidney [72-74]. In the process of aging, the strontium/calcium ratio in urine decreases rapidly until about 25 weeks of age, followed by a much slower decrease [5]. 

A. PROBING WESTERN BLOTS WITH RADIOACTIVE CALCIUM This procedure is adapted from that of Maruyama et al. (1984). 

Hsiao, S. C., and H. Boroughs. 1958. The uptake of radioactive calcium by sea urchin eggs. I. Entrance of Ca into unfertilized egg cytoplasm. Biol. Bull. 114(2) 196-204. 

Kowal, N. E., and D. A. Crossley, Jr. 1971. The ingestion rates of microarthropods in pine mor, estimated with radioactive calcium. Ecology 52(3) 444-452. 

McCabe, R. A., and G. A. LePage. 1958. Identifying progeny from pheasant hens given radioactive calcium (Ca ). J. Wildl. Manage. 22(2) 134-141. 

Shuvalov, V. S. 1959. Experiment with radioactive calcium ( Ca) in the study of inorganic fertilization of ponds. In Transactions of the 6th Conference on the Biology of Inland Waters (B. S. Kuzin and S. I. Kuznetsov, eds.). Publishing House of the USSR Academy of Science, Moscow and Leningrad. [English translation AEC-tr-6880, pp. 33-40 (1969).]... 

Calcium is excreted in both feces and urine, about 80% of the total amount excreted being in feces and 20% in the urine. Fecal calcium consists of unabsorbed calcium together with calcium which has been absorbed and re-excreted. It has been generally assumed that the large intestine is the major site of excretion into the intestines, but recent experiments with radioactive calcium have demonstrated that in the rat all segments of the intestinal tract are active in this function with the small intestine predominating. Calcium is excreted in urine mainly as chlorides and phosphates, and in feces as phosphate, carbonate, and soaps. 

In these experiments toad blatter tissue from Bufo Marinus was loaded up with Ca by incubation for 60 min. in a toad Ringer fluid, after which washout-curves for the radioactive calcium were obtained. When hormone was added to the medium during the washout procedure, there was a sudden increase in the release of to the medium. This increased release was... 

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