caa a22 4500 477119654 CHVBK 20180405111632.0 cr unu---uuuuu 170330e19960301xx s 000 0 eng 10.1007/BF00240026 doi (NATIONALLICENCE)springer-10.1007/BF00240026 Deformation of the Bowditch staircase in Ca2+-overloaded mammalian cardiac tissue — a calcium phenomenon? [Elektronische Daten] [Matthias Löhn, Gerhard Szymanski, Fritz Markwardt] Concentrations of 1-4 μmol l−1 isoproterenol cause both in right ventricular papillary muscles and in enzymatically isolated myocytes of the guinea-pig a Ca2− overload-induced state which is functionally characterized by biphasic (multiphasic) twitches and biphasic (multiphasic) intracellular calcium transients, respectively, during excitation-contraction coupling. This state was stabilized in the in vitro experiments for some hours by a co-ordination of the interstimulus interval, the temperature of the superfasion fluid and the addition of calcium agonists. The functional stability is the precondition for the reproducibility of the experimental results particularly after the application of long-lasting stimulation programmes. Changes in the shape of biphasic contractions were compared with changes in the time course of biphasic intracellular calcium transients using three manipulations of a different kind: (1) the interruption of the steady pacing rhythm, (2) the variation of the interstimulus interval, (3) the addition of ryanodine. It was shown that: (1) The BOWDITCH staircase in calcium overloaded multicellular preparations is changed in that each individual component of the twitch passes through its own staircase. A homologous behaviour can be observed in the configuration of the phasic and tonic component of biphasic intracellular calcium transients. (2) At different driving frequencies the relative proportion of the two components of a biphasic twitch corresponds to the time integrals of the two components of biphasic intracellular calcium transients. (3) Ryanodine suppresses both the first component of the biphasic twitch and the phasic component of the biphasic intracellular calcium transient. The SR Ca2+-ATPase inhibitor thapsigargin increases the second component of the biphasic calcium transient. This supports the hypothesis that the size of the tonic component is in part determined by intracellular calcium reuptake. The results of both kinds of experiments would be compatible with the assumption that in calcium overloaded mammalian cardiac cells calcium reaches the contractile system directly as well as via two intracellular stores (‘extended two-Ca-store concept'). Kluwer Academic Publishers, 1996 e-c coupling nationallicence Ca-overloaded myocytes nationallicence biphasic Ca-transients nationallicence ryanodine nationallicence thapsigargin nationallicence isoproterenol nationallicence Löhn Matthias Julius-Bernstein-Institut für Physiologie, Martin-Luther-Universität Halle-Wittenberg, Halle, Germany aut Szymanski Gerhard Julius-Bernstein-Institut für Physiologie, Martin-Luther-Universität Halle-Wittenberg, Halle, Germany aut Markwardt Fritz Julius-Bernstein-Institut für Physiologie, Martin-Luther-Universität Halle-Wittenberg, Halle, Germany aut Molecular and Cellular Biochemistry Kluwer Academic Publishers; http://www.wkap.nl 160-161/1(1996-03-01), 13-25 0300-8177 160-161:1<13 1996 160-161 11010 https://doi.org/10.1007/BF00240026 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/BF00240026 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Löhn Matthias Julius-Bernstein-Institut für Physiologie, Martin-Luther-Universität Halle-Wittenberg, Halle, Germany aut NATIONALLICENCE 700 1- Szymanski Gerhard Julius-Bernstein-Institut für Physiologie, Martin-Luther-Universität Halle-Wittenberg, Halle, Germany aut NATIONALLICENCE 700 1- Markwardt Fritz Julius-Bernstein-Institut für Physiologie, Martin-Luther-Universität Halle-Wittenberg, Halle, Germany aut NATIONALLICENCE 773 0- Molecular and Cellular Biochemistry Kluwer Academic Publishers; http://www.wkap.nl 160-161/1(1996-03-01), 13-25 0300-8177 160-161:1<13 1996 160-161 11010 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer