Nitric oxide-induced mobilization of intracellular calcium via the cyclic ADP-ribose signaling pathway

Abstract

Cyclic adenosine diphosphate ribose (cADPR) is a potent endogenous calcium-mobilizing agent synthesized from β-NAD + by ADP-ribosyl cyclases in sea urchin eggs and in several mammalian cells (Galione, A., and White, A. (1994) Trends Cell Biol. 4, 431-436). Pharmacological studies suggest that cADPR is an endogenous modulator of Ca 2+-induced Ca 2+ release mediated by ryanodine-sensitive Ca 2+ release channels. An unresolved question is whether cADPR can act as a Ca 2+-mobilizing intracellular messenger. We show that exogenous application of nitric oxide (NO) mobilizes Ca 2+ from intracellular stores in intact sea urchin eggs and that it releases Ca 2+ and elevates cADPR levels in egg homogenates. 8-Amino-cADPR, a selective competitive antagonist of cADPR-mediated Ca 2+ release, and nicotinamide, an inhibitor of ADP-ribosyl cyclase, inhibit the Ca 2+-mobilizing actions of NO, while, heparin, a competitive antagonist of the inositol 1,4,5- trisphosphate receptor, did not affect NO-induced Ca 2+ release. Since the Ca 2+-mobilizing effects of NO can be mimicked by cGMP, are inhibited by the cGMP-dependent-protein kinase inhibitor, R(p)-8-pCPT-cGMPS, and in egg homogenates show a requirement for the guanylyl cyclase substrate, GTP, we suggest a novel action of NO in mobilizing intracellular calcium from microsomal stores via a signaling pathway involving cGMP and cADPR. These results suggest that cADPR has the capacity to act as a Ca 2+-mobilizing intracellular messenger.