Vitamin D status and brush border membrane vesicles: 1,25-dihydroxyvitamin D3 induced destabilization

Abstract

Purified chick duodenal brush border membrane vesicles (BBMV) were used to assess the effect of vitamin D on intestinal Ca²⁺ 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 Ca²⁺ uptake. In vivo treatment with 1,25(OH)₂D₃ results in an 85% increase in the V_max of Ca²⁺-uptake from 2.2 to 3.9 nmol/min/mg protein. The K_m of Ca²⁺-uptake (0.9 mM) 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 Ca²⁺ 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.