Figure 2.

Purinergic independent and dependent signaling in the vascular cell. Purinergic receptor (P2R) independent pathway: Vascular cells degrade ATP into adenosine monophosphate (AMP) and pyrophosphate (PP_i) by ecto-nucleotide pyrophosphatase/phosphodiesterase (NPP1). The potent calcification inhibitor PPi blocks arterial calcification, however, PP_i itself can also be broken down into the calcification stimulator inorganic phosphate (P_i) by tissue non-specific alkaline phosphatase (TNAP). P2R dependent pathway: ATP also inhibits arterial calcification by interaction with P2 receptors, being P2Y and P2X receptors, expressed on the extracellular membrane of vascular cells. Solid and dashed arrows represent respectively stimulatory and inhibitory arrows.