単離平滑筋細胞を用いた細胞内Ca2+放出機構の解析 : 単離平滑筋細胞の薬理

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This paper briefly reviews our current effort to study the Ca2+ mobilization mechanism in enzymatically dispersed single smooth muscle cells. Each single cell obtained from guinea pig taenia caeci possesses two types of Ca2+ stores, one (Sα) with both Ca2+-induced and IP3-induced Ca2+ release mechanisms and the other (Sβ) with only IP3-induced Ca2+ release mechanism. After depletion of Sα either with ryanodine treatment or with caffeine pretreatment, carbachol failed to induce Ca2+ release, while intracellular application of IP3 did induce Ca2+ release. Our results suggest that the difference between the agonist and IP3-induced responses can be resolved by obligatory involvement of positive feedback control of IP3-induced Ca2+ release in the agonist-induced Ca2+ release. Furthermore, we were able to demonstrate that the dose-response relation in single cells shows an all-or-none feature, which seems at least partly due to the feedback control of Ca2+ release. We discuss the reasons why graded dose-response relation is obtained in bundles of smooth muscles, while the response of single cells is an all-or-none type.