EFFECTS ON SKELETAL MUSCLE 



201 



various conditions, the state of rigor produced is likely to be the same in 

 each. The basis for the kinetics of rigor is metabolic and must be conceived 

 of in terms of changes in a fairly complex multienzyme system (page 227). 



Fig. 1-18. Effects of temperature changes on the re- 

 laxation of frog muscle in rigor from treatment with 

 iodoacetate. (From Aubert and Rombaut, 1953.) 



(B) Reversibility of iodoacetate rigor. Initially it was believed that the 

 rigor produced by iodoacetate cannot be reversed, and this is certainly true 

 to the extent that the muscle cannot be restored to its normal length and 

 excitability. Furthermore, an unloaded muscle will remain in rigor indefi- 

 nitely (probably until autolysis). However, if the muscle is loaded, it will 

 spontaneously and slowly relax from the state of rigor (Lippay and Patzl, 

 1935; Aubert and Rombaut, 1953; Sandow and Schneyer, 1955). Frog mus- 

 cle suspended in 0.4 mM iodoacetate under tension goes into contracture 

 fairly rapidly, but relaxation soon occurs; the rate of relaxation is depen- 

 dent on the temperature (Fig. 1-18) (Aubert and Rombaut, 1953), possibly 

 indicating some reaction or process upon which relaxation is based, and is 

 more rapid when the muscle is well washed (Lippay and Loning, 1935), 

 which was interpreted to mean that some diffusible substance is formed in 



