Regulation of Cell Functions by Ca2+ Oscillation
Since the initial discovery of the regulatory role of intracellular Ca2+ signals in skeletal muscle contraction (Ebashi and Endo, 1968; Ebashi et al., 1969), the list of cellular functions that are regulated by Ca2+ signals has expanded. Now, it is recognized that intracellular Ca2+ signals are involved in the regulation of various cell functions including fertilization, secretion, transcription, immunity, learning and memory (Berridge et al., 2000). One of the striking features of Ca2+ signals is that they display complex spatiotemporal distributions such as Ca2+ waves and oscillations. An oscillatory change in Ca2+ concentration was first observed in skinned fiber experiments by Endo and collaborators in 1970 (Endo et al., 1970). When skinned skeletal muscle fibers were immersed in a solution mimicking intracellular conditions and caffeine was added to the solution at millimolar concentrations, the skinned fibers underwent periodic contractions because of the periodic release of Ca2+ from the sarcoplasmic reticulum, in the absence of membrane potential changes. With the advent of methods of measuring intracellular Ca2+ concentration, Ca2+ oscillation has been observed in many types of intact cell. In 1986, Cobbold and collaborators (Woods et al., 1986) observed Ca2+ oscillation in agonist-stimulated hepatocytes using aequorin, a Ca2+-sensitive luminescent protein. The introduction of fluorescent Ca2+ indicators further facilitated the observation of intracellular Ca2+ transients (Tsien, 1988). Initially, the physiological significance of Ca2+ oscillation was not fully appreciated, because they were observed only in cell lines or in isolated cells.
KeywordsNuclear Translocation Myosin Light Chain Myosin Light Chain Phosphatase Smooth Muscle Myosin Light Chain Myosin Light Chain Phosphatase Activity
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