Abstract
To estimate myofibrillar responsiveness to Ca2+, we used the relation between cell length and intracellular [Ca2+] ([Ca2+]i) during tetanic contractions of isolated ventricular myocytes. Enzymatically isolated rat ventricular myocytes were loaded with fura-2 AM (4 µM for 10 min) and excited alternately at 340 nm and 380 nm. The ratio (R) of fura-2 fluorescence at these wavelengths [F(340)/F(380), an index of [Ca2+]i] and cell length (L) were measured simultaneously. Following treatment with thapsigargin (0.2 µM), myocytes were stimulated at 10 Hz for 10 s to produce a tetanic contraction every min and an instantaneous plot of R vs L (R-L trajectory) was constructed. The R-L trajectory followed the same path during cell shortening and re-lengthening, suggesting that dynamic equilibrium between R and L was achieved during tetanus. Increasing the extracellular [Ca2+] from 1 to 8 mM extended the R-L trajectory without a substantial shift of the relation. The Ca2+-sensitizing thiadiazinone derivative, EMD57033 (1 µM), shifted the R-L trajectory to the left (sensitization of the myofibrils to Ca2+), whereas the non-selective phosphodiesterase inhibitor, 3-isobutyl-1-methylxantine (200 µM), shifted the R-L trajectory to the right (desensitization of the myofibrils to Ca2+), in agreement with previous results obtained using skinned preparations. We conclude that the R-L trajectory is useful for estimating the myofibrillar responsiveness to Ca2+ in isolated myocytes and may be beneficial for the evaluation of inotropic agents.
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Received: 13 March 1998 / Received after revision: 4 May 1998 / Accepted: 2 June 1998
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Hongo, K., Kusakari, Y., Konishi, M. et al. Estimation of myofibrillar responsiveness to Ca2+ in isolated rat ventricular myocytes. Pflügers Arch 436, 639–645 (1998). https://doi.org/10.1007/s004240050683
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DOI: https://doi.org/10.1007/s004240050683