1,25-dihydroxyvitamin D3 stimulates vesicular transport within 5 s in polarized intestinal epithelial cells

Controversy remains regarding whether the seco-steroid hormone 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) enhances calcium and phosphate movement across the intestinal epithelial cell by facilitated diffusion or a vesicular transport mechanism. In this study we investigated whether membrane trafficking, as judged by confocal microscopy, was sufficiently rapid in comparison to hormone-stimulated uptake of phosphate (32P). Primary cultures of chick intestinal cells were established overnight either in Petri dishes (uptake studies) or chambered coverslips (confocal microscopy). Addition of 130 pM 1,25(OH)2D3 resulted in an apparent increase in 32P uptake within 1 min, relative to controls, that was statistically significant from 3-10 min of incubation. Using the endocytic marker dye, FM1-43, confocal microscopy revealed a profound decrease in membrane-associated fluorescence (apical> basal) within 10 s of hormone treatment, a return of fluorescence at 15-65 s, followed by another round of decreasing and increasing fluorescence. Between 3-9 min of incubation, fluorescence intensity increased 50% (apical region) and 20% (basal region) over control conditions. An antibody (Ab 099) directed against a putative membrane receptor for 1,25(OH)2D3 (1,25D3-MARRS) inhibited both 32P uptake, and changes in fluorescence. In addition, the protein kinase C (PKC) inhibitor, calphostin C, inhibited both 32P uptake and the observed 1,25(OH)2D3-mediated changes in fluorescence. At the microscopic level, calphostin C pretreatment abolished the very rapid redistribution of the endocytic marker dye, although a slight increase in fluorescence was still observed. We conclude that 1,25(OH)2D3-stimulated vesicular trafficking is mediated by the 1,25D3-MARRS protein, implicates a PKC signaling mechanism, and occurs in a time frame that is commensurate with a role in ion transport.