EFFECTS ON SKELETAL MUSCLE 



199 



relaxation) induction process, which is essentially what is often called exci- 

 tation-contraction coupling, iodoacetate slows this process; this is not due 

 to a rise in pH, which has the opposite effect, but may be related to the fall 

 in ATP concentration. The difference L — Lr, which is the time for relax- 

 ation, is decreased by iodoacetate; this shortening is interpreted in terms of 



Fig. 1-17. Effects of 0.068 milf iodoacetate on the 

 contractile characteristics of muscle using maximal 

 tetani of 3 sec duration. The symbols are the same 

 as in Fig. 1-16. (From Sandow and Karczmar, 1950.) 



a more rapidly developing tension induction process (which is rather sur- 

 prising), due perhaps to the effects of a rise in pH on ATPase activity. There 

 is some question whether the pH changes occurring are of sufficient magni- 

 tude to produce any of the effects observed. It should be noted that iodo- 

 acetate does not significantly affect latent period behavior unless there is a 

 period of tetanic activity. 



Muscle Rigor Produced by Iodoacetate 



Various substances and types of metabolic disturbance can produce a 

 state of rigor in muscle, but iodoacetate remains the classical and most 



