Nucleotides are key subunits for nucleic acids and provide energy for intracellular metabolism. They can also be released from cells to act physiologically as extracellular messengers or pathologically as danger signals. Extracellular nucleotides stimulate membrane receptors in the P2 and P1 family. P2X are ATP-
activated cation channels; P2Y and P1 are G-protein coupled receptors activated by
ATP, ADP, UTP and UDP or adenosine, respectively. Renal P2 receptors influence both vascular contractility and tubular function. Renal cells also express
ectonucleotidases that rapidly hydrolyze extracellular nucleoti des. These enzymes integrate this multi-receptor purinergic-signaling complex by determining the nucleotide milieu, as well as titrating receptor activation.

Purinergic signaling also regulates immune cell function by modulating the synthesis and release of various cytokines such as IL1-β and IL-18 as part of inflammasome activation. Abnormal or excessive stimulation of this intricate paracrine system can be pro- or anti-inflammatory, and is also linked to necrosis and apoptosis. Kidney tissue injury causes a localized increase in ATP concentration, and sustained activation of P2 receptors can lead to renal glomerular, tubular and vascular cell damage. Purinergic receptors also regulate the activity and proliferation of
fibroblasts, promoting both inflammation and fibrosis in chronic disease.
In this short review we summarize some of the recent findings related to purinergic signaling in the kidney. We focus predominantly on the P2X7 receptor, discussing why antagonists have so far disappointed in clinical trials and how advances in our understanding of purinergic signaling might help to reposition these compounds as potential treatments for renal disease.