Cyclic ADP-Ribose contributes to contraction and Ca2+ release by M1 muscarinic receptor activation in coronary arterial smooth muscle

The present study determined the role of cyclic ADPribose (cADPR) in mediating vasoconstriction and Ca2+ release in response to the activation of muscarinic receptors. Endothelium-denuded small bovine coronary arteries were microperfused under transmural pressure of 60 mm Hg. Both acetylcholine (ACh; 1 nmol/L to 1 mumol/L) and oxotremorine (OXO; 2.5-80 mumol/L) produced a concentration-dependent contraction. The vasoconstrictor responses to both ACh and OXO were significantly attenuated by nicotinamide (Nicot; an ADP-ribosyl cyclase inhibitor), 8-bromo-cADPR (8-Br-cADPR; a cADPR antagonist) or ryanodine (Ry; an Ry receptor antagonist). Intracellular Ca2+ ([Ca2+](i)) was determined by fluorescence spectrometry using fura-2 as a fluorescence indicator. OXO produced a rapid increase in [Ca2+](i) in freshly isolated single coronary arterial smooth muscle cells (CASMCs) bathed with Ca2+-free Hanks' solution. This OXO-induced rise in [Ca2+](i) was significantly reduced by pirenzepine (PIR; an M-1 receptor-specific blocker), Nicot, 8-Br-cADPR or Ry. The effects of OXO on the activity of ADP-ribosyl cyclase (cADPR synthase) were examined in cultured CASMCs by measuring the rate of cyclic GDP- ribose (cGDPR) formation from beta-nicotinamide guanine dinucleotide. It was found that OXO produced a concentration-dependent increase in the production of cGDPR. The stimulatory effect of OXO on ADP-ribosyl cyclase was inhibited by both PIR and Nicot. These results suggest that the cADPR signaling pathway participates in the contraction of small coronary arterial smooth muscle and Ca2+ release induced by activation of M-1 muscarinic receptors. Copyright (C) 2003 S. Karger AG, Basel.