Calcium metabolism in HeLa cells and the effects of parathyroid hormone.

Calcium metabolism was investigated in HeLa cells. 90% of the calcium of the cell monolayer is bound to an extracellular cell coat and can be removed by trypsin-EDTA. The calcium concentration of the naked cell, freed from its coat, is 0.47 mM. The calcium concentration of the medium does not affect the concentration of the naked cell calcium. However, the calcium of the cell coat is proportional to the calcium concentration in the medium. Calcium uptake into the cell coat increases with increasing calcium concentration of the medium, whereas uptake by the naked cell is independent of the calcium of the medium. Anaerobic conditions and metabolic inhibitors do not inhibit calcium uptake by the cell, a fact suggesting that this transfer is a passive phenomenon. The calcium in the extracellular cell coat, was not affected by parathyroid hormone. In contrast, the hormone increased the cellular calcium concentration by stimulating calcium uptake or by enhancing calcium binding to some cell components. These results suggest that, contrary to current thinking, parathyroid hormone influences the cellular calcium balance by mobilizing calcium from the extracellular fluids in order to increase its concentration in some cellular compartment. It is proposed that these effects can enhance calcium transport.