The cytosolic Ca²⁺ concentration ([Ca²⁺]_c) controls diverse cellular events via complex Ca²⁺ signalling patterns. Interactions between Ca²⁺ release channels on the SR and between the SR and other organelles such as mitochondria establish the characteristics of the Ca²⁺ signal. Here, in single voltage-clamped colonic smooth muscle cells, IP₃-generating agonists evoked either repetitive Ca²⁺ oscillations or propagated waves. The forward movement of the Ca²⁺ wave arose from Ca²⁺-induced Ca²⁺ release (CICR) at the IP₃ receptor (IP₃R) without ryanodine receptor involvement. A functional compartmentalization of the SR store produced by an increase in [Ca²⁺]_c,rendered the site of IP₃-mediated Ca²⁺ release, alone, refractory to the phosphoinositide and accounted for the decline in [Ca²⁺]_c at the back of the wave. Notwithstanding the unique recruitment of IP₃R in wave development, waves are modulated by mitochondrial activity. Collapsing the mitochondrial membrane potential (necessary for Ca²⁺ uptake by mitochondria) inhibited Ca²⁺ oscillations and waves. These inhibitory effects on oscillations and waves could be explained by mitochondrial regulation of IP₃-mediated Ca²⁺ release itself. Thus collapsing the mitochondrial membrane potential inhibited IP₃mediated Ca²⁺ release. Mitochondria may accumulate Ca²⁺ to maintain a low local [Ca²⁺] near the IP₃R to prevent a Ca²⁺-dependent negative feedback on the receptor and so sustaining IP-mediated Ca²⁺ release. These results raise the possibility that IP₃-mediated Ca²⁺ release may compromise ATP production as a result of mitochondrial depolarisation. However, neither Ca²⁺ influx (transient or sustained) or release of Ca²⁺ via IPR significantly altered the mitochondrial membrane potential. On the other hand, repetitive oscillations and waves transiently depolarised some mitochondria (<5%). These depolarisations were neither synchronised with the [Ca²⁺]_c changes or with events occurring in adjacent mitochondria. Thus repetitive Ca²⁺ changes appear necessary to evoke significant mitochondrial depolarisation and mitochondria themselves appear to be independent units in smooth muscle.