The Disposition of Calcium within Parathyroid Tissue

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Abstract
The disposition of 45Ca was studied in equine parathyroid gland slices. This preparation was shown to be viable by its ability to carry out protein synthesis, by the responsiveness of its respiration to effectors of oxidative phosphorylation, and by its Ca-inhibitable PTH [parathormone] secretion. 45Ca accumulates in the slices as the extracellular Ca is raised through the range in which physiological serum Ca concentration lies. The tissue slices behave as if they have no Ca pump: depriving the cells of energy by treatment with antimycin A does not admit more Ca to the tissue, a significant displaced by La, and a divalent cation ionophore [A23187, calcimycin] does not expose new Ca binding sites. An energy-dependent sequestration of Ca by the tissue seems unlikely: Ca is very rapidly taken up, more is taken up at 0.degree. C than at 37.degree. C and antimycin A does not affect the amount of Ca retained. Evidently the parathyroid gland passively accumulates Ca, and it is held intracellularly by a substance with a dissociation constant in the millimolar range.

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