Extracellular ADP‐ribose Induces [ca2+]i Increase Via Purinergic Pathway in Pulmonary Artery Smooth Muscle Cells (1175.4)

ADP‐ribose (ADPR) is the product of NAD metabolism and cyclic ADPR hydrolysis by CD38, and poly(ADPR) degradation by poly(ADPR) glycohydrolase. It is recognized as a signaling molecule for the activation of the transient receptor potential melastatin 2 (TRPM2) channel and play important roles in H2O2 induced response. In the plasma membrane, CD38 catalytic site orients both extra‐ and intracellularly. Hence, ADPR can be generated and release outside of the cells. However, the role of extracellular ADPR is unclear. Recent studies suggest that ADPR can activate purinergic receptors in pancreaticβcells. Here we examined the Ca2+ mobilizing effect of extracellular ADPR in rat pulmonary artery smooth muscle cells (PASMCs). Application of ADPR (30 µM to 1 mM) elicited concentration dependent increase in [Ca2+]i of PASMCs. At 1 mM, ADPR induced Ca2+ response with a transient and a sustained phase. The sustained phase was abolished by the removal of extracellular Ca2+. Suramin (a non‐selective P2 receptor antagonist) attenuated ADPR‐induced sustain phase, and PPADS (a P2X receptor antagonist) inhibited the peak response. MRS2179 (a selective P2Y1 receptor inhibitor) had no effect on ADPR‐induced Ca2+ mobilization. The PLC inhibitor U73122, but not its inactive analog U73343, inhibited the ADPR‐induced response by 70%. U73122 plus PPADS further decreased the ADPR‐induced peak response. 2‐APB inhibited ADPR‐induced peak response but not the sustain phase. These data indicate that ADPR is an agonist of purinergic receptors, and it mobilizes [Ca2+]i via P2 receptor‐PLC‐IP3R calcium release pathway, but not through TRPM2‐mediated Ca2+ entry. (Supported by R01 HL071835 and R01 HL075134)