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1. lODOACETATE AND lODOACETAMIDE 



The only thorough investigation of the effects of iodoacetate on muscle 

 contraction is that of Sandow and Karczmar (1950) and is essentially con- 

 fined to the latent period. A muscle relaxes slightly before an increase in 

 tension begins (Fig. 1-16), and Sandow has described these changes in terms 

 of the three cellular processes indicated in the figure. A brief tetanus ap- 

 plied to a frog muscle leads to a state in which normal stimuli induce a 



FiCx. 1-10. Latent period changes of skeletal 

 muscle, according to Sandow and Karczmar 

 (1950). L = latent period; Lj^ = mechanically 

 quiescent latency relaxation induction; and 

 R = latency relaxation. 



greater than normal tension and the latency relaxation (E) is depressed; 

 it requires 30-45 min for the muscle to return to normal (Fig. 1-17). These 

 alterations may be associated in part with changes in the intracellular pH 

 brought about by the disturbed metabolism and the breakdown of ATP 

 and creatine-P. If a muscle is treated with iodoacetate (0.068 mM), the 

 rise in posttetanic tension is less and the tension soon falls below normal, 

 and progressively decreases to zero as rigor develops. The latency relaxation 

 does not return toward normal but decreases further and eventually disap- 

 pears. One may say that the effects of tetanic activity on the latent period 

 characteristics are greater in the iodoacetate-treated muscle. 



With respect to the time relations of these processes, iodoacetate pro- 

 duces characteristic changes (Fig. 1-17). The latency for tension output (L) 

 is decreased by iodoacetate and does not return to normal during the post- 

 tetany period, but the relaxation latency (Lr) is unchanged by either tet- 

 any or iodoacetate for around 7 min, although in the iodoacetate-treated 

 muscle it then increases markedly. If one equates Lr with the LR (latency 



