64 



S. KOREY 



VOL. 4 (1950) 



and the concentrations used. The degree of shortening on addition of standard ATP was 

 compared with control fibers. To determine the possibiHty of simultaneous activation 

 of the contractile process, test solutions of adrenaline, acetylcholine and histamine were 

 prepared in ATP standard. These were added to fibers which had been previously 

 soaked in corresponding solutions without ATP. None of the compounds enumerated 

 affected the ATP induced contraction, whether the fibers were exposed to them prior 

 to the contact with ATP or simultaneously. 



TABLE IV 



COMPOUNDS WHICH H.^D NO EFFECT IN THE CONTRACTIONS 



INDICATED ON THE NON-CONDUCTING MUSCLE FIBER (RABBIT) 



NOR CHANGED THE ATP INDUCED ISOTONIC CONTRACTION. 



TIME OF EXPOSURE : 30-60 MIN 24° C 



DISCUSSION 



The Szent-Gyorgyi preparation may be considered a prototype of the contractile 

 elements of normal muscle. For the study of contraction, it is intermediate between 

 the intact cell and isolated systems (and proteins) in solution. Since the structure of 

 the preserved iibers appears similar to the normal, they probably retain a considerable 

 degree of the orientation and organization of the contractile proteins originally present. 

 Partly for this reason, contraction rather than extension, as seen in the randomly 

 constituted myosin threads, occurs after the addition of ATP to the loaded iibers. Also 

 the supportive action of the sarcolemma mechanically prevents separation of the 

 fibrils' contractile units while they are undergoing spatial rearrangement associated 

 with the process of contraction. 



ATP and ADP but not adenylic acid cause contraction of the fibers. Quantitative 

 relationships between concentrations of ATP and ADP and the degree of shortening of 

 the fibers require further investigations. It is apparent, however, that ATP is at least 

 10 times more effective in causing shortening than an equivalent amount of ADP. 

 Since no enzyme is known to exist in muscle which splits ADP, the effect obtained with 

 ADP may appear surprising. In previous observations reported ADP preparations were 

 not entirely free of significant amounts of ATP and the action of such preparations could 

 be attributed to ATP. The preparation of ADP used in these experiments was free of 

 ATP, as tested enzymatically. However, it is possible that the ADP was converted by 

 myokinase to ATP prior to its action. The fibers have not been examined for the pre- 

 sence of this enzyme. 



Under the conditions of the present experiments, contraction of the fibers was not 

 followed by comparable relaxation despite washings in solution containing NaCl, KCl, 

 References p. 6y. 



