Potentiation and hysteresis induced by stretch and subsequent release of papillary muscle of the dog

¹ Department of Physiology, University of Louisville School of Medicine, Louisville, Kentucky

Isolated papillary muscle of the dog was placed in an oxygenated Ringer's solution bath maintained at 36°C, and isometric recordings of resting tension and developed tension were obtained for stretched muscle and for subsequently released muscle. The hysteresis loop produced by stretch and subsequent release of resting papillary muscle resembles closely the hysteresis loop obtained by stretch and subsequent release of skeletal muscle. This means that the length-resting tension curve obtained by release of papillary muscle falls considerably below the similar curve obtained by stretch of this muscle. A comparison of the length-developed tension curves for stretched and subsequently released papillary muscle shows that developed tension is potentiated in released muscle at all observed lengths, the range of length being 100–148% of equilibrium length. The average of maximum developed tension was 164.7 gm/cm² in 20 experiments with stretched papillary muscles and 228.8 gm/cm² in 20 experiments with the same muscles released immediately after stretch.