抄録
Interstitial cells (IC) are now considered to play a key role in pacemaking in gastrointestinal (GI) tissues. Regardless of the varied sensitivity to L-type Ca channel blockers, slow waves in GI smooth muscles are readily blocked by the disruption of intracellular Ca handling. IC are also identified in spontaneously active smooth muscles of the urinary tract and corporal tissues. In the urethra, isolated IC spontaneously discharge electrical events which are very similar to those recorded from intact smooth muscles, suggesting that IC may be pacemaking the smooth muscle. In the bladder, IC generate spontaneous Ca transients which occur independently from those of smooth muscles. Moreover, the initiation of spontaneous excitation almost solely depends on L-type Ca channels without significant contribution of intracellular Ca stores, indicating that the spontaneous activity may be initiated by detrusor smooth muscle cells rather than IC. In corporal tissues, IC are abundantly distributed in the smooth muscle meshwork. Spontaneous Ca transients and contractions are blocked by either L-type Ca channel blockers or by disrupting Ca store function. In addition, the spontaneous activity is prevented by inhibiting cyclooxygenase-2 (COX-2), suggesting that they result from the local synthesis of prostaglandin. Therefore, although IC are widely distributed in smooth muscles of the lower urinary tract and corporal tissues, the mechanism which is involved in generating spontaneous excitation appear to vary between tissues, indicating a diversity of the physiological significance of IC. [Jpn J Physiol 55 Suppl:S24 (2005)]
