Regulation of cellular calcium metabolism and calcium transport by calcitonin.

Calcitonin was studied in isolated kidney cells and in isolated mitochondria. A concentration of 10 ng/ml of synthetic calcitonin increases the cellular accumulation of 45Ca and the total cell calcium. The mitochondrial pool is increased several-fold. Kinetic analysis of the data shows that although the total cellular exchangeable calcium pool is enlarged, calcium influx and efflux are significantly depressed by calcitonin. The absence of phosphate or the presence of inhibitors of mitochondrial calcium transport completely abolish the effects of the hormone. In isolated mitochondria, the hormone stimulates the active calcium uptake and depresses the extramitochondrial calcium activity. Calcitonin counteracts the effects of cyclic AMP which stimulates the release of calcium from mitochondria and increases the extramitochondrial calcium activity. These data indicate that cellular calcium homeostasis is controlled by the mitochondrial calcium turnover. They suggest that calcitomin regulates the cell calcium metabolism and inhibits the transcellular calcium transport by stimulating the rate of calcium uptake by mitochondria which depresses cytoplasmic calcium activity.