The mechanism of calcium transport by rat intestine

Short-circuit techniques for the study of ion transport by isolated membrane systems have been applied to defining the mechanism for calcium ion transport in the small intestine of the rat. In the absence of phosphate, the movement of calcium is passive. There is no evidence for a membrane-bound carrier to facilitate its transport. The calcium flux is a linear function of its concentration. However, phosphate ion is actively transported from the mucosal to the serosal surface. In the presence of phosphate, calcium appears to be actively transported, possibly as a counter-ion to the phosphate. The role of chelation in the transport of calcium has also been clarified.