STUDIES ON RAPID COOLING CONTRACTURE OF FROG TOE MUSCLE IMMERSED IN HYPERTONIC AND HYPOTONIC SOLUTIONS

Abstract

The tension development of rapid cooling contracture (RCC) of toe muscle of Rana nigromaculata treated with 1.0 mM caffeine invarious hypertonic or hypotonic solutions was measured by mechanoelectrictransducer. The tension output of RCC decreased in hypertonic NaCl solution in which the concentration of NaCl was increasedand in hypertonic solution prepared by addition of KCl to the normalRinger solution. The RCC tension output was not altered in isotonicsolution in which NaCl was isotonically substituted for KCl in normalRinger solution, but it decreased in test solution in which KCl washypertonically increased. However, the RCC tension output was notaltered in a solution in which urea was hypertonically added to thenormal Ringer solution. The RCC tension output increased in hypotonic solution prepared byreducing the concentration of NaCl in normal Ringer solution; its valuewas maintained at an osmotic strength of 200-210m O sm/kg H₂O andwas reduced at 160m O sm/kg H₂O. In conclusion, the tension development of rapid cooling contracturein hypertonic and hypotonic solutions was similar to the data on crayfishmuscle (APRIL et al., 1968), in which the ionic strength of the intracellularspace is a major determinant of the mechanical response to agiven activation of Ca mechanical coupling.