Nitric oxide inhibits Ca2+ mobilization through cADP-ribose signaling in coronary arterial smooth muscle cells

The present study was designed to determine whether the cADP-ribose-mediated Ca2+ signaling is involved in the inhibitory effect of nitric oxide (NO) on intracellular Ca2+ mobilization. With the use of fluorescent microscopic spectrometry, cADP-ribose-induced Ca2+ release from sarcoplasmic reticulum (SR) of bovine coronary arterial smooth muscle cells (CASMCs) was determined. In the alpha-toxin-permeabilized primary cultures of CASMCs, cADP-ribose (5 mu M) produced a rapid Ca2+ release, which was completely blocked by pretreatment of cells with the cADP-ribose antagonist 8-bromo-cADP-ribose (8-Br-cADPR). In intact fura 2-loaded CASMCs, 80 mM KCl was added to depolarize the cells and increase intracellular Ca2+ concentration ([Ca2+](i)). Sodium nitroprusside (SNP), an NO donor, produced a concentration-dependent inhibition of the KCl-induced increase in [Ca2+](i), but it had no effect on the U-46619-induced increase in [Ca2+](i). In the presence of 8-Br-cADPR (100 mu M) and ryanodine (10 mu M), the inhibitory effect of SNP was markedly attenuated. HPLC analyses showed that CASMCs expressed the ADP-ribosyl cyclase activity, and SNP (1-100 mu M) significantly reduced the ADP-ribosyl cyclase activity in a concentration-dependent manner. The effect of SNP was completely blocked by addition of 10 mu M oxygenated hemoglobin. We conclude that ADP-ribosyl cyclase is present in CASMCs, and NO may decrease [Ca2+](i) by inhibition of cADP-ribose-induced Ca2+ mobilization.