EFFECTS ON SKELETAL MUSCLE 



207 



reported by Fleckenstein et al. (1950), Macfarlane and Meares (1958), and 

 Musclioll (1959). Muscholl found about a 60% depression of the potential 

 at maximal rigor, but rigor began early and was well over half developed 

 before the potential began to fall significantly (Fig. 1-20). Godeaux (1949) 

 could detect no general depolarization during the development of rigor. 



Fig. 1-20. Effects of 2.7 mM iodoacetate on the resting potential and 

 isotonic shortening (rigor) of rat diaphragm. (From Muscholl, 1959.) 



The most accurate and reliable results were obtained by Ling and Gerard 

 (1949), using transmembrane recording with microelectrodes. Iodoacetate 

 produces a slow fall of the resting potential over 4 hr (from 80 mv to around 

 64 mv) and during this period rigor develops to its maximal value. The 

 potential rises somewhat and then rather precipitously falls to zero. Inas- 

 much as a correlation between muscle creatine-P and degree of initial de- 

 polarization (characterizing the A potential) was observed, it was thought 

 that reduction in the creatine-P might be responsible for the early fall in 

 the potential. But in any event, all of the work points quite conclusively to 

 the fact that depolarization is not the primary cause of rigor induced by 

 iodoacetate, although possibly in some instances it may contribute. 



Muscle action potentials and after-potentials are generally more sensitive 

 to iodoacetate than the resting potential. Positive after-potentials are de- 

 pressed (Schaefer and Scholmerich, 1938), the magnitude of the action po- 

 tential is reduced (Gluckman and Koff, 1955), and there is a lengthening 

 of the action potential duration, due to a slowing of the repolarization (Mac- 



