A Cell Permeable NPE Caged ADP-Ribose for Studying TRPM2

Transient potential receptor melastatin-2 (TRPM2) is a non-selective Ca2+-permeable cation channel of the TRPM channel subfamily and is mainly activated by intracellular adenosine diphosphate ribose (ADPR). Here we synthesized a 1-(2-nitrophenyl)ethyl caged ADPR (NPE-ADPR) and found that uncaging of NPE-ADPR efficiently stimulated Ca2+, Mg2+, and Zn2+ influx in a concentration-dependent manner in intact human Jurkat T-lymphocytes. The cation influx was inhibited by inhibitors or knockdown of TRPM2. Likewise, uncaging of NPE-ADPR markedly induced cation entry in HEK 293 cells that overexpress TRPM2. As expected, high temperature increased the ability of the photolyzed NPE-ADPR to induce cation entry, whereas acidic pH inhibited. Moreover, the absence of extracellular Ca2+ significantly inhibited Mg2+ and Zn2+ influx after uncaging NPE-ADPR. On the other hand, the absence of extracellular Na+ or Mg2+ had no effect on photolyzed NPE-ADPR induced Ca2+ entry. Taken together, our results indicated that NPE-ADPR is a cell permeable ADPR analogue that is useful for studying TRPM2-mediated cation entry in intact cells.