Introduction: The urinary bladder has two major functions, the storage and voiding of urine. The first requires relaxation of the urinary bladder detrusor smooth muscle during bladder filling; the latter requires coordinated contraction. Urinary bladder smooth muscle (UBSM) contraction occurs through the initiation of action potentials within the parasympathetic nerves leading to the bladder, which evokes the release of the excitatory neurotransmitters acetylcholine (ACh) and adenosine trisphosphate (ATP). The general thought is that ACh and ATP act independently through muscarinic (M2, M3) and purinergic (P2X1) receptors, respectively, to increase excitability and contractility {1, 2}. Methods: Electrical field stimulation (EFS) was used to stimulate nerves in isolated mouse UBSM strips. The resulting changes in force and calcium signalling were measured with myography and the calcium-sensitive dye Fluo-4, using a laser scanning confocal microscope. Purinergic and muscarinic receptors were inhibited with α,β-methylene ATP/suramin and atropine, respectively. Results: P2X1 receptors are cation channels, whereas M2, M3 receptors are coupled to G-proteins {3}. Consequently, because purinergic signalling acts through an electrical mechanism, one might predict that it would be activated earlier following EFS than cholinergic signalling. Calcium imaging experiments on intact UBSM strips showed the presence of at least three different calcium events during and 2-3s after EFS; 1) Elementary purinergic events, which reflect ATP release from nerve varicosities and activation of P2X1 receptors {4}; 2) Fast “global” calcium flashes with calcium entry through voltage-dependent calcium channels {4} and 3) Slower calcium waves, which likely reflect activation of IP3 receptors. Calcium flashes occurred during and after EFS. Inhibition of muscarinic receptors eliminated calcium flashes that occurred after EFS without effecting calcium flashes during stimulation. In contrast, inhibition of purinergic receptors eliminated calcium flashes during stimulation and greatly augmented the number of flashes after stimulation. These results indicate that rapid purinergic signalling suppresses the slower cholinergic-mediated increases in excitability and hence calcium entry. Therefore, inhibiting P2X1 receptors should slow force generation but lead to overall elevation in force. Indeed, in the presence of purinergic inhibitors, both the rise time and the decay time of EFS-induced contractions were prolonged, indicating increased UBSM contractility. Conclusion: Under physiological conditions, rapid purinergic signalling represents not just an independent contraction-inducing pathway, but it also suppresses slower cholinergic effects on UBSM. The consequence is that changes in purinergic signalling affect subsequent cholinergic-mediated contractility through changes in calcium signalling.