Cyclic ADP-ribose (cADPR) is an endogenous Ca(2+)-mobilizing second messenger in many cell types and organisms. Although the biological activity of several modified analogues of cADPR has been analyzed, most of these structures were still very similar to the original molecule. Recently, we have introduced simplified analogues in which the northern ribose (N(1)-linked ribose) was replaced by an ether strand. Here we also demonstrate that the southern ribose (N(9)-linked ribose) can be replaced by an ether strand resulting in N(1)-[(phosphoryl-O-ethoxy)-methyl]-N(9)-[(phosphoryl-O-ethoxy)-methyl]-hypoxanthinecyclic pyrophosphate (cIDP-DE). This minimal structural analogue of cyclic ADP-ribose released Ca(2+) from intracellular stores of permeabilized Jurkat T lymphocytes. In intact T lymphocytes initial subcellular Ca(2+) release events, global Ca(2+) release, and subsequent global Ca(2+) entry were observed. Cardiac myocytes freshly prepared from mice responded to cIDP-DE by increased recruitment of localized Ca(2+) signals and by global Ca(2+) waves.