The role of CFTR in transepithelial liquid transport in pig alveolar epithelia

摘要

vitamin d and its essential role in curing rickets was discovered in the early part of the last century. The term vitamin is actually a misnomer as vitamin D is better characterized as a pre-pro-hormone (see Fig. 1A for chemical modifications required for hormonal activity). Figure IB illustrates where in the body vitamin D is modified and gives examples of target tissues. Vitamin D from the diet or from the UV-mediated conversion of 7-dehydro-cholesterol in the skin is hydroxylated by the liver in the 25 position to generate calcidiol (25-hydroxy vitamin D). This form of vitamin D serves as a pro-hormone. It circulates in serum, predominantly bound to the vitamin D binding protein, with a half-life of at least a couple of weeks in humans (http://www.drugbank.ca/drugs/DB00146) and is used to determine the vitamin D status. Currently, calcidiol levels of about 20 ng/ml (50 nM) are considered optimal for supporting health (8; http://www.iom.edu/Reports/2010/Dietary-Reference-Intakes-for-Calcium-and-Vitamin-D.aspx).