Abstract
We attempted to introduce calcium regulation into in vitro motility assay. Cardiac thin filament was reconstituted from actin and tropomyosin-troponin complex purified from rat myocardium separately. Double staining of the filaments showed tropomyosin-troponin complex was integrated along actin filaments homogeneously. The reconstituted thin filaments were made to slide on cardiac myosin fixed on a glass coverslip in the presence of MgATP while varying free Ca2+ concentration of the medium ([Ca2+]). Filaments showed only Brownian motion when [Ca2+] was below 10−6.4 M. However, filaments slid at a constant velocity when [Ca2+] exceeded 10−6.4 M, showing that the sliding was regulated in an on-off manner. The threshold [Ca2+] increased to 10−5.0 M under acidic conditions, indicating a decrease in Ca2+ sensitivity of the contractile proteins. Simple actin filaments slid at a constant velocity independently of [Ca2+], demonstrating that the regulatory proteins were responsible for this on-off manner regulation. This new assay technique may be a powerful tool to directly evaluate the Ca2+ sensitivity of the contractile apparatus and to investigate how cardiac contraction is regulated by Ca2+.
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Sata, M., Yamashita, H., Sugiura, S. et al. A new in vitro motility assay technique to evaluate calcium sensitivity of the cardiac contractile proteins. Pflugers Arch. 429, 443–445 (1995). https://doi.org/10.1007/BF00374162
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DOI: https://doi.org/10.1007/BF00374162