2-Chloro-ATP sodium (2-Chloro ATP) is an adenine nucleotide and an analog of ATP. It is an antagonist of the purinergic P2Y1 receptor and inhibits intracellular calcium mobilization induced by ADP in Jurkat cells expressing the human receptor (Ki=2.3 μM). 2-Chloro-ATP sodium is an agonist of the purinergic P2X receptor and induces inward currents in HEK293 cells expressing human bladder smooth muscle or rat PC12 forms of the receptor (EC50=0.5 and 2.5 μM). 2-Chloro-ATP sodium induces relaxation of precontracted guinea pig cecal strips in a concentration-dependent manner. 2-Chloro-ATP sodium has been used to study the substrate specificity of cyclic nucleotide-dependent protein kinases such as protein kinase A ( PKA ) and PKG.