Acta Biochimica et Biophysica 16. (1981)
1981 / 3-4. szám - Proceedings of the Eleventh Conference on Biophysics. Abstracts
236 Proceedings of the 1 Ith Conference of Biophysics Membrane Potential Dependent Calcium Transients and Birefrigence Signals in Skeletal Muscle Fibres G. Szűcs, L. Kovács, R. A. Schümperli Department of Physiology, Medical University, Debrecen and Institute of Physiology, University of Berne, Switzerland The birefrigence signals and Ca2+ transients evoked by depolarizing pulses were studied simultaneously in voltage clamped cut muscle fibres of the frog Rana esculenta (T = 2 — 4 °C). Changes in birefrigence were measured with crossed polarizers at 790 nm wave length. Using the métallochromie indicator dye antipyrylazo III intracellular Ca2+ transients were recorded at 720 nm. The birefrigence signals had longer latency times, reached their peak value later and decreased slower than the corresponding Ca2+ transients evoked by depolarizing pulses of the same amplitude and duration. The peak values of the signals showed the same voltage dependence in both cases. The results suggest that birefrigence transients do not reflect the changes in the membrane potantial of the sarcoplasmic reticulum but rather follow the changes in the intracellular Ca2+ concentration. In most cases the falling phase of the birefrigence signals has a much slower time course than the change in the myoplasmic free Ca2+ indicating, thus, the role of other processes in eliciting the birefrigence changes. Shortening of A Bands in Mammalian Heart Muscle K. Trombitás, E. Rőth, B. Török Central Laboratory and Department of Experimental Surgery, Medical University, Pécs Many morphological investigations proved that, even in case of very different muscle lengths the length of the A band did not change perceptibly either during stretch or during isotonic or isometric contraction. Changes in the length of the sarcomere are accounted for by changes in the length of the I bands alone. On the other hand a severe ischemic injury followed by reperfusion gave rise to the development of supercontracted bands in the papillary muscle of mammalian heart. The striated pattern of the muscle could hardly be recognized in the supercontracted bands any more, and the contractile proteins aggregated irreversibly. It seems very probable that also the myofilaments themselves could become shorter under similar circumstances. This phenomenon could be demonstrated by the effect of slight ischemic injury, applied after hypothermic potassium cardioplegia plus reperfusion. In this case two distinct types of muscle shortening could be observed: Acta Biochimica et Biophysica Academiae Scientiarum Hungaricae 16, 1981