Normal detrusor smooth muscle contractions are elicited by a rise of intracellular [Ca²⁺] via activation of second messenger signalling pathways. These signalling cascades release Ca²⁺ from intracellular stores to activate contractile proteins. Contraction can be modulated by molecules such as cAMP, where a rise in cAMP levels has shown to reduces contractile force (Wheeler et al. 1995). Adenosine-specific P1-receptors are linked to adenylate cyclase activity and could have a role in contractile modulation. Male Dunkin-Hartley guinea-pigs were humanely killed by cervical dislocation. Bladder tissue was dissociated with a solution of digestive enzymes according to previously determined protocols (Wu et al. 2002). Isolated cells were loaded with a fluorescent indicator; fura-2 and cell suspensions were placed onto a microscope stage and superfused at 37°C in HCO₃^–/CO₂ Tyrode’s solution (pH7.35). Ca²⁺-transients were stimulated with 3μM carbachol (acetylcholine analogue). Effect of the adenylate cyclase inhibitor, MDL-12330A, was investigated on Ca²⁺-transients in the presence of adenosine. All compounds were from Sigma UK and, with the exception of adenosine, were made as stocks in DMSO and diluted in Tyrode’s solution to working concentrations. Data are expressed as mean±S.D., (n) is number of experiments, Student’s t test was used to test for significance between data sets (*p<0.05). Previous results (Ikeda et al. 2004) indicated Ca²⁺-transients may be modulated by the A2b-subtype of P1-receptors. 1μM DPCPX (A1-specific antagonist), 1μM 8-(3-chlorostyryl)caffeine (A2a-specific antagonist) and 1μM MRS-1191 (A3-specific antagonist) with 1mM adenosine reduced transients by 34±31% (n=6), similar to reduction with adenosine alone, 30±26% (n=15), confirming A2b-receptors are involved in adenosine-mediated reductions. MDL-12330A reduced Ca²⁺-transients dose-dependently (0.03-3μM), with a maximal reduction of 47±22% (n=8). 1μM MDL-12330A reduced Ca²⁺-transients by 30±31% (n=5) and 1mM adenosine with MDL-12330A were reduced by 39±31% (n=4), therefore possibly affecting similar pathways. Adenosine or MDL-12330A alone did not significantly reduce transients elicited by 80mM KCl-Tyrode’s [adenosine (n=3), MDL (n=6)] or 20mM caffeine [adenosine (n=8), MDL (n=6)]. cAMP can modulate Ca²⁺-transients elicited by muscarinic-receptor activation. Results here show A2b-receptors can also modulate Ca²⁺-transients, possibly through modulation of adenylate cyclase activity.