Smooth muscles in the urinary tract and corporal tissue exhibit spontaneous contractile activity. Although this activity was assumed to be generated within smooth muscle cells (SMCs), it is now known that ICs, which share characteristics with ICC, the primary pacemaker cells in the gastrointestinal (GI) tract, are involved. In the urethra, isolated ICs generate spontaneous electrical activity, which are very similar to those of the intact urethra, suggesting that they may act as electrical pacemakers. Spontaneous Ca transients in urethral ICs in situ had a lower frequency (3 min−1) and a longer half-width (4 s) than those in SMCs (10 min−1 and less than 1 s, respectively). IC Ca transients depend on the release of Ca from intracellular stores and require the influx of Ca through non L-type Ca channel pathways. However ICs, did not form an extensive network nor consistently triggered Ca transients in adjacent SMCs, suggesting that signal transmission from ICs to SMCs in the urethra may be much less extensive than between ICC and SMCs. Interestingly, low frequency (1 min−1),long duration (5-15s) Ca transients are recorded in ICs of the bladder, where SMCs generate spontaneous action potentials, and in ICs of the renal pelvis where atypical SMCs appear to provide the main pacemaker drive. Therefore, ICs in the urinary tact may be divisible into subpopulations in which ICs with a slower time course play a non-pacemaking role. Indeed, ICs in corporal tissue release prostaglandins via cyclooxygenase-2 activity to reinforce spontaneous activity initiated by SMCs. [J Physiol Sci. 2007;57 Suppl:S15]
