Cultured smooth muscle cells from rabbit urinary bladder were loaded with fura-2. Changes in intracellular Ca concentration [Ca2+](i) produced by acetylcholine (ACh) or adenosine triphosphate (ATP) were estimated by measuring the fluorescence ratio F340/F380. Western blot analysis and immunohistochemical techniques showed that the cultured cells retained α- smooth muscle actin. ATP produced a rapid but transient increase in [Ca2+](i) and ACh produced a delayed, prolonged increase. Application of ACh after ATP in Ca-free solution failed to elevate [Ca2+](i) suggesting that both ACh and ATP release Ca2+ from the same intracellular stores. Following application of ACh but not ATP in Ca-free Krebs solution, reintroduction of Ca2+ produced elevation of [Ca2+](i), indicating that ACh causes prolonged opening of channels in the membrane. The sustained increase induced by ACh was abolished by nicardipine (blocker of Ca2+ voltage dependent channel I(Ca(V))) or quinine (blocker of non-selective cation channels). Although the elevations to ACh or ATP were abolished by neomycin (an inbibitor of phospholipase C) the different time courses suggest that the mechanisms of release of Ca2+ from intracellular stores or the pathway for refilling the stores is different.
All Science Journal Classification (ASJC) codes
- Clinical Neurology