Vitamin D status and brush border membrane vesicles: 1,25‐dihydroxyvitamin D 3 induced destabilization

Purified chick duodenal brush border membrane vesicles (BBMV) were used to assess the effect of vitamin D on intestinal Ca 2+ transport and membrane stability. BBMV preparations are right‐side‐out as judged by a nine‐fold increase in accessibility of lactoperoxidase to core material actin in the presence of Triton X‐100. Freshly prepared BBMV from vitamin D‐deficient chicks support both sodium‐dependent glucose transport and Ca 2+ uptake. In vivo treatment with 1,25(OH) 2 D 3 results in an 85% increase in the V max of Ca 2+ ‐uptake from 2.2 to 3.9 nmol/min/mg protein. The K m of Ca 2+ ‐uptake (0.9 m M ) is independent of the vitamin D status of the chick. The majority of BBMV derived from vitamin D‐replete chicks were destabilized and rendered incapable of supporting either sodium‐dependent glucose uptake or Ca 2+ uptake if they were held at 0–4°C for 2 to 24 h. In 40 separate experiments, 80% of membranes derived from vitamin D‐replete chicks showed characteristics of destabilization, whereas only 24% of all control membranes exhibited a lack of viability.