Analyzing contractile responses in demembranized pig papillary muscle fibers: The influence of calcium, resting force, and temperature

The influence of calcium, resting force and temperature on the contractile behaviour in isolated demembranized ('skinned') pig papillary muscle fibers (n = 36) was analysed. Demembranisation excludes the influence of any membrane related processes on the contractile response as the myofilaments are in direct contact with the bathing medium. Resting force (1 mN - 9 mN), temperature (22°C or 32°C) and pCa 7.0 - 4.3 were varied and the contractile response was analyzed by studying the time constant and the extent of post vibration force recovery (PVFR) of the activated preparations (the vibration method). Additional constant-load experiments and detection of sarcomere-length were carried out. There was an inverse-linear relationship between time constants of post vibration force recovery and maximum shortening velocity as estimated by constant load experiments. Resting force affected the extent of force development but not the time constant of post vibration force recovery and modulated the pCa-force relationship without altering the calcium concentration required for halfmaximal activation (calcium sensitivity). In contrast lowering the bath temperature from 32°C to 22°C caused a significant leftward shift of the pCa-force relationship potentially due to changes of the contractile filaments' calcium sensitivity. The effect of temperature on the myocardial contractile system is of special interest as hypothermia is frequently used in cardiac surgery. Analysis of alterations of the contractile proteins' calcium sensitivity during the rewarming period of the patient may provide further insight in the pathophysiology of reperfusion. Application of the vibration method in skinned myocardial muscle fibres as a research instrument to characterize alterations of contractility on the contractile apparatus level is a new approach for analyzing the mechanisms underlying impaired myocardial function.