Accumulation of Ca45 by slices of the small intestine

Respiring slices of the proximal small intestine of the rat accumulate Ca45 in vitro, and after 1 hour of incubation at 37°C the Ca45 concentration ratio tissue/medium is approximately 5. When oxidative metabolism is prevented by incubation under N2, or when the generation of phosphate-bond energy is inhibited with 2,4-dinitrophenol, the corresponding Ca45 ratio tissue/medium is approximately 2. The oxygen-dependent accumulation of Ca45 is limited in capacity, relatively specific for Ca++ in contrast to Sr++ or Ba++, inhibited by K+, and dependent on the dietary vitamin D. It is greater with slices from young, growing rats than with those from older rats. The results indicate that the accumulation of Ca45 by slices results mainly from the active transfer of calcium previously observed with everted gut-sacs.