The subcellular location of H 3 vitamin D 3 in kidney and intestine

Abstract

An investigation of the subcellular distribution of vitamin D 3 in rat kidney, liver, and intestinal mucosa was carried out utilizing radiochemically pure H 3-vitamin D 3 All tissues were examined 24 hours following the oral administration of 500 IU of H 3-vitamin D 3 to vitamin D-deficient rats. The tissues were fractionated into nuclear, mitochondrial, microsomal, and cytoplasmic fractions via conventional differential centrifugation techniques. Approximately equal amounts of radioactivity were found in the nuclear, mitochondrial, and microsomal fractions, while very little was found in the cytoplasmic fraction. When the radioactivity was expressed on a weight basis (dpm/100 mg dry weight of fraction), the microsomal fractions from the kidney and intestinal mucosa, but not that from the liver, were significantly higher than the corresponding mitochondrial fractions which in turn were significantly higher than the nuclear fractions. The radioactivity in mitochondria and microsomes was shown by thin layer chromatography to be predominantly in a material indistinguishable from crystalline vitamin D 3. Sonication or mild deoxycholate treatment of mitochondria and microsomes failed to release any of the H 3-vitamin D from these particles. Instead the vitamin D remained with “membrane-rich” fragments which are recovered by centrifugation at 105,000 g for 90 minutes. These results indicate that the vitamin D present in kidney and intestine following a physiological dose of the vitamin is tightly bound to subcellular membranes.