EFFECT OF DEVELOPED TENSION ON THE TIME COURSES OF CA2+ TRANSIENTS AND TENSION IN TWITCH CONTRACTION IN FERRET MYOCARDIUM

Objectives: The aim of the study is to test the hypothesis that tensio n-dependent change in the affinity of cardiac troponin-C influences th e time courses of Ca2+ transients and tension in twitch contraction. M ethods: The Ca2+-sensitive photoprotein, aequorin, was microinjected i nto superficial cells of ferret papillary muscles and the Ca2+ transie nts and tension were simultaneously measured. The peak of developed te nsion was altered by changing the extracellular Ca2+ concentration, in itial muscle length, and the application of 2,3-butanedione monoxime. Results: In each maneuver, the decay time of Ca2+ transients was prolo nged and the tension relaxation time was shortened when the peak of de veloped tension was decreased. In contrast, when the peak of developed tension was increased, the decay rime of Ca2+ transients was shortene d and the tension relaxation time was prolonged, The decay time of Ca2 + transients measured with different maneuvers was negatively correlat ed with the peak tension and the tension relaxation time was positivel y correlated with the tension peak. Conclusions: The changes in the de cay lime of Ca2+ transients and the tension relaxation time indicate t hat developed tension modulates the affinity of troponin-C for Ca2+ in normal which contraction.