In vitro use of vitamin D3 metabolites: culture conditions determine cell uptake.

This report demonstrates that routine variations in cell culture conditions dramatically affect the amount of vitamin D3 metabolites to which cultured cells have access. Increasing the concentration of a metabolite in the medium increases the amount of the metabolite in the cell compartment. Increasing the volume of medium in the culture dishes (while maintaining a constant metabolite concentration) also increases the amount of metabolite in the cell compartment. Moreover, daily changes of the medium containing fresh metabolite increase the amount of the metabolite in the cell compartment as well. These variables may explain the inability of different laboratories to duplicate dose-response curves.