420 IMMUNO-CATALYSIS 



on striated muscle; ATP initiates contraction and changes birefringence 

 when apphed in minute amounts to isolated striated muscle fibers of 

 the frog, thus establishing the breakdown of ATP as the reaction near- 

 est in time to contraction. On the other hand, the breakdown of phos- 

 phocreatine is believed to produce during nerve activity sufficient 

 energy for the electric action potential. It has been calculated that a 

 single nerve impulse requires only 1/50,000 of the energy of a muscle 

 twitch (A. V. Hill, cited by Nachmansohn, 1945). 



In in vitro studies, Jordan and Oster (1948) reported that in potas- 

 sium chloride solution ATP induces the coiling of actomyosin. They 

 consider the ATP-actomyosin interplay of fundamental importance in 

 muscular contraction. The function of potassium in this reaction is, 

 likewise, of critical significance. 



The observation of Cantoni and Eastman (1946) that histamine 

 and acetylcholine, etc. depress the contractile responsiveness of the 

 intestinal strip of guinea pig may suggest that these agents are inter- 

 fering with the above mentioned critical roles of potassium in the 

 metabolism of muscle. This interference is overcome or antagonized 

 by an increase in the concentration of potassium ion in the systems 

 studied. In this connection, reference may be made to the possibly re- 

 lated observation of Rocha e Silva and Beraldo (1948). They re- 

 ported that potassium ion accelerates the antihistaminic action of 

 pyribenzamine, neo-antergan, antistin, benadryl, etc. on the guinea pig 

 ileum suspended in tyrode solution. Magnesium ion, on the contrary, 

 had a strong decelerating eflfect; calcium ion in general exercised a 

 predominantly depressing effect; strontium ion, even when present 

 in the low concentration of 0.0025 molar, had a definite accelerating 

 effect on the antihistaminic action of the drugs. 



Buchthal and his associates have studied the interaction of acetyl- 

 choline and ATP on striated and smooth muscles of mammals. ATP 

 or ADP in amounts of 10~^/tg, applied to the curarised or non-curarised 

 isolated muscle of the frog produces tetanus-like contractions which 

 are accompanied by action potentials. Also, in curarised and non- 

 curarised striated and smooth muscles of mammals, contractions are 

 released when the substance is applied by close arterial injection (Buch- 

 thal, 1947). Intra-arterial injection of acetylcholine decreases the 

 electrical excitability and changes the strength-duration curve of muscle 

 for a considerable time after its application. Previous application of 



