. Calcified tissues; proceedings. Bone; Collagen; Calcification. 5 mg/hour SI Dwly exchan bone Ca 61 mg ged Bound cell Ca 16 me Excretion + bone formation. Ditfusible cell Ca mg and dvnamics in the duced into the blood plasma rapidly exchanges with "interstitial calcium" located in interstitial fluid and connective tissue. Interstitial calcium is itself submitted to much slower exchange reactions with tissue calcium and is continuously renewed by uni- directional processes; resorption from bone and absorption supply calcium which is lost by deposition in bone and excretion. Non-e
. Calcified tissues; proceedings. Bone; Collagen; Calcification. 5 mg/hour SI Dwly exchan bone Ca 61 mg ged Bound cell Ca 16 me Excretion + bone formation. Ditfusible cell Ca mg and dvnamics in the duced into the blood plasma rapidly exchanges with "interstitial calcium" located in interstitial fluid and connective tissue. Interstitial calcium is itself submitted to much slower exchange reactions with tissue calcium and is continuously renewed by uni- directional processes; resorption from bone and absorption supply calcium which is lost by deposition in bone and excretion. Non-extracellular tissue calcium is dis- tributed in three compartments in which the exchange rates are very different diffusible calcium, bound calcium and slowly exchangeable bone calcium. Diffusible and bound calcium have been identified in soft tissues (smooth and striated muscle) but the corresponding compartments shown in Fig. 1 are larger than the calcium content of the soft tissues of the whole rat. In growing rats some of the exchangeable fractions of bone calcium are included in diffusible and bound compartments since their exchange rates are respectively equal to the one of diffusible and bound cellular calcium (Stoclet and Cohen, 1963). The specific activity of calcium contained in each compartment has been calcu- lated at the different experimental times and compared with the specific activity of aorta calcium at the same time. Fig. 2 shows the variations with time of the specific activity of calcium in the aorta (R. ), in "interstitial" rapidly exchangeable com- partment (R. S.) and in slowly exchangeable compartment (R. S. 4). The plain line represents the calculated curve for the following distribution of aorta calcium: rapidly exchangeable (extracellular) per g, slowly exchangeable (like bone calcium) //M per g and non-exchangeable calcium tiM per g. This calculated curve has been plotted from â '^Ca radioactivity in the aorta at tw
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