Interstitial Cells of Cajal (ICC) are recognised as the pacemaker cells that are responsible for the generation and co-ordination of electrical slow waves that underlie the phasic contractile activity of the gut (Sanders et al., 2006). However, ICC have also been reported in regions outside the gut, such as the ureters, urethra and bladder (Klemm et al., 1999; Sergeant et al., 2000 and McCloskey & Gurney, 2002). ICC in the urethra are thought to act as putative pacemaker cells, which may be involved in the generation of spontaneous myogenic tone. Freshly dispersed ICC from the rabbit urethra display spontaneous transient inward currents (STICs) under voltage clamp and spontaneous transient depolarisations (STDs) under current clamp (Sergeant et al., 2000). This activity is associated with global Ca²⁺ waves (Johnston et al, 2005) and the cellular mechanisms responsible for their regulation and generation has been partly elucidated. For example, it was shown that inhibition of ryanodine receptors (RyRs) abolished the activity, whereas inhibition of inositol trisphosphate (IP3) production or IP3 receptors (IP3Rs) reduced the propagation of Ca²⁺ waves, unmasking multiple, uncoupled Ca²⁺ release events. Ca²⁺ waves were also found to be dependent on Ca²⁺ influx, thus removal of extracellular Ca²⁺ inhibited Ca²⁺ waves by a mechanism that did not involve depletion of Ca²⁺ from stores (Johnston et al., 2005 and Bradley et al., 2005). Spontaneous Ca²⁺ waves and STICs in urethral ICC were also found to be inhibited by agents which decrease mitochondrial Ca²⁺ uptake, such as FCCP, CCCP, antimycin A, rotenone and RU360 (Sergeant et al., 2008. Conversely, when mitochondrial Ca²⁺ uptake was enhanced using the mitochondrial uniporter activator kaempferol, the frequency of Ca²⁺ oscillations was increased. This effect was inhibited by FCCP, consistent with an action on mitochondria. Application of the ATP synthase inhibitor, oligomycin, did not inhibit Ca²⁺ oscillations suggesting that the effects of the uptake inhibitors were not due to an effect on ATP synthesis. Therefore, the cellular basis of pacemaker activity in urethral ICC is a complex process depending on Ca²⁺ release from stores and Ca²⁺ influx across the plasma membrane. We propose that these events are regulated by Ca²⁺ uptake by mitochondria.