Active transport of calcium by the small intestine of the rat

The rates of active transport of calcium in vitro by everted gut-sacs prepared from the proximal small intestine of the rat have been quantified and expressed in absolute units. A maximal rate of transport has been measured. The bulk of the calcium transferred to the serosal surface of the gut-sac is ionized calcium, suggesting that the process is an active cation transport mechanism. The active transfer is relatively specific for Ca++, and no significant accumulation of Mg++, Sr++, Ba++ or K+ in the fluid bathing the serosal surface could be demonstrated. The active transport of calcium in vitro is greater with gut-sacs from growing than from older rats, and it is greater with gut-sacs from pregnant than from nonpregnant rats. The results suggest that the active transport mechanism can increase the intestinal absorption of calcium facultatively to meet the needs of the organism.