938 7. MERCURIALS 



inhibits muscle cholinesterase, it was concluded that the fibrillation results 

 from inhibition of cholinesterase, allowing acetylcholine to accumulate 

 (Kuschinsky and LiiUmann, 1954). None of the other actions of mersalyl 

 appears to be related to this inhibition. The delayed relaxation was claimed 

 to be similar to that produced by veratrine but, if so, it does not provide 

 much information on the mechanism, since one is ignorant of how vera- 

 trine acts. 



Contracture of frog muscle by Hg++ had been noted by Bacq (1942), 

 Beck and Bein (1948), and Krueger (1950). Bacq assumed this to be an 

 effect such as that given by iodoacetate, i.e., a Lundsgaard effect due to 

 glycolytic inhibition, but Krueger showed that Hg++, in contrast to iodo- 

 acetate, does not bring about a reduction in lactate concentration during 

 rigor. Kuschinsky and Liillmann (1954) found that mersalyl causes a rapid 

 loss of muscle K+ and attributed the initial rapid contracture to a depola- 

 rization of the fibers, a conclusion shared by Muscholl (1958), who demon- 

 strated a fall in the membrane potential coincident with contracture. How- 

 ever, the delayed contracture must have another origin and, although Kus- 

 chinsky and Liillmann postulated a Lundsgaard mechanism, there is no 

 evidence one way or the other. The action potential traces presented by 

 Muscholl (1958) show that mersalyl reduces the magnitude so that the over- 

 shoot is lost, slows both depolarization and repolarization, and hence pro- 

 longs the duration of the action potential, effects quite different than those 

 seen in heart (page 945). Frog muscle after-potentials seem to be unaffect- 

 ed by mercurials between 0.1 and 2 mM (Macfarlane and Meares, 1958). 

 Contracture by mersalyl is dependent on Ca++ in the medium, but this 

 may be true for most types of contracture (Kutscha, 1961). 



The contraction of glycerinated muscle fibers by ATP is inhibited by 

 Hg++ at concentrations around 0.01-0.1 mM (Godeaux, 1944, Korey, 

 1950; Hasselbach, 1953; Edman, 1958) and by mersalyl at similar con- 

 centrations (Portzehl, 1952; Edman, 1959). A preparation contracted by 

 ATP is relaxed upon addition of the mercurial. These effects are irrever- 

 sible by washing or treatment with cysteine. Weber and Portzehl (1954) 

 suggested that the inhibition of the ATP effect is due to a block of ATPase 

 so that ATP can act only as a plasticizer, but there is also, according to 

 Edman (1958), a direct effect since there is some relaxation in the absence 

 of ATP. 



A great deal of work has been done on the behavior of muscle contractile 

 proteins exposed to mercurials, and the importance of SH groups has been 

 conclusively demonstrated. The effects of the mercurials are summarized in 

 Table 7-20. Both actin and myosin possess SH groups of differing degrees of 

 reactivity and function. In the complexing of actin and myosin to form 

 actomyosin, it is the SH groups of myosin which are important (Bailey 

 and Perry, 1947; Kuschinsky and Turba, 1951). Bailey and Perry felt that 



