The present invention relates to methods and compositions comprising small interfering RNAs (siRNAs) to identify nucleotides encoding proteins involved in the co-transport of inorganic phosphate in vascular tissues. Specifically, it relates to the identification of Pit-1 and Pit-2 as key proteins involved in vascular calcification, the deposition of calcium phosphate, in blood vessels. The nucleic acids encoding specific siRNAs and vectors encoding these siRNAs are useful as tools to specifically inhibit the expression of Pit-1, Pit-2, or related proteins in various primary and stably-transformed cell lines, and as tools to explore the roles and functional relationships of these proteins involved in vascular calcification. In addition, they may be useful directly as therapeutic agents in humans delivered to sites of vascular calcification.