平滑筋の自発活動における間質細胞の役割

抄録

Many smooth muscles exhibit spontaneous electrical and mechanical activity. This has been considered to "myogenic" activity for many years, however, it is in fact generated by specialized cells, namely interstitial cells of Cajal (ICC). In the gastrointestinal tract, a network of myenteric ICC (ICC-MY) generates pacemaker potentials to initiate spontaneous electrical activity. Intramuscular ICC (ICC-IM) augment the depolarizations by generating ongoing unitary potentials (UPs). However, corporal ICC-IM may be dominant pacemaker as they create a greatest frequency in spontaneous activity. ICC-like cells have been found in other smooth muscle organs and may play a similar role. In the urethra, ICC-like cells generate spontaneous transient depolarizations (STDs), which sum to activate L-type Ca channels. UPs and STDs result from the opening of Ca-activated Cl⁻ channels. UPs solely depend on inositol 1, 4, 5-trisphosphate (InsP₃)-dependent Ca release, whilst the generation of STDs requires both InsP₃- and ryanodine-receptors. In corpus cavernosum (CC), where smooth muscle cells are capable of generating spontaneous depolarizations, ICC-like cells express cyclooxygenase 2 and spontaneously produce prostaglandins to reinforce spontaneous activity. Therefore, although ICC or ICC-like cells in different regions or tissues share many similarities, they also have a significant diversity. Interaction between ICC and smooth muscle cells result in a further heterogeneity of spontaneous activity, and thus develops characteristics of individual smooth muscle organs. [J Physiol Sci. 2006;56 Suppl:S54]