Adenosine triphosphate--dependent calcium uptake by rat submaxillary gland microsomes.

Microsomes from rat submaxillary glands are able to take up calcium from the suspension media. Calcium uptake is greatly increased by the presence of ATP. This effect of ATP is not detected at 0 degrees C. ADP cannot replace ATP to potentiate calcium uptake. ATP-dependent calcium uptake is not observed in the absence of magnesium. ATP-dependent calcium uptake is enhanced by oxalate and, to a lesser degree, by inorganic phosphate. Total calcium per milligram of microsomal protein observed when tests were performed without oxalate closely parallels the amounts for skeletal and cardiac muscles reported by several authors. Calcium uptake in salivary gland microsomes is slower than in muscle microsomes. Speculations are considered about the role of ATP-dependent calcium uptake. It is suggested that a decrease in intracellular free calcium levels returns these cells to the resting state after secretion.