Agonists such as muscarinic receptor activators are normally thought to induce contraction in smooth muscle through IP3 production, and release of Ca2+ from sarcoplasmic reticulum (SR). However, cADPR and NAADP may also be involved in this process, the former acting on the SR, the latter on lysosome-related organelles. This study investigated the functions of cADPR and NAADP, and their roles in carbachol (CCh) contractions in β-escin permeabilized guinea pig detrusor and taenia caecum. IP3 (50 µM), cADPR (50 µM) and NAADP (1 µM) induced contraction in both tissues. Heparin (1 mg/ml) blocked contractions by IP3 but not by cADPR or NAADP. Thapsigargin (T, 5 µM) + ryanodine (R, 100 µM) inhibited responses to both cADPR and IP3, but not to NAADP. NAADP contractions were blocked by inhibitors bafilomycin (0.1 µM) or high concentration of NAADP (100 µM). CCh (50 µM) contraction in both tissues was reduced by heparin but not completely abolished. T + R were able to abolish this CCh response in taenia, but T + R + NAADP (100 µM) were necessary to completely abolish the contraction in detrusor. These results show that cADPR and NAADP have a role in Ca2+signalling in detrusor and taenia. While IP3 and cADPR are important in CCh contractions in both tissues, NAADP is involved only in detrusor. Thus, key differences in Ca2+ signalling mechanisms are apparent between two different smooth muscles of the same species. [ABSTRACT FROM AUTHOR]