Extracellular cyclic ADP-ribose potentiates ACh-induced contraction in bovine tracheal smooth muscle

Cyclic ADP-ribose (cADPR), a universal calcium releaser, is generated from NAD(+) by an ADP-ribosyl cyclase and is degraded to ADP-ribose by a cADPR h ydrolase. In mammals, both activities are expressed as ectoenzymes by the t ransmembrane glycoprotein CD38. CD38 was identified in both epithelial cell s and smooth myocytes isolated from bovine trachea. Intact tracheal smooth myocytes (TSMs) responded to extracellular cADPR (100 muM) with an increase in intracellular calcium concentration ([Ca2+](i)) both at baseline and af ter acetylcholine (ACh) stimulation. The nonhydrolyzable analog 3-deaza-cAD PR (10 nM) elicited the same effects as cADPR, whereas the cADPR antagonist 8-NH2-cADPR (10 muM) inhibited both basal and ACh-stimulated [Ca2+](i) lev els. Extracellular cADPR or 3-deaza-cADPR caused a significant increase of ACh-induced contraction in tracheal smooth muscle strips, whereas 8-NH2-cAD PR decreased it. Tracheal mucosa strips, by releasing NAD(+), enhanced [Ca2 +](i) in isolated TSMs, and this increase was abrogated by either NAD(+)-as e or 8-NH2-cADPR. These data suggest the existence of a paracrine mechanism whereby mucosa-released extracellular NAD(+) plays a hormonelike function and cADPR behaves as second messenger regulating calcium-related contractil ity in TSMs.