1951). Dephosphorylization of ATP to adenosine- 

 diphosphate (ADP) is believed to be the most 

 important reaction closely connected to the libera- 

 tion of energy in the contracting muscle. The 

 function of ATP, according to Weber (1958) is 

 twofold: "it acts as a contracting substance if it 

 is split and as a relaxing and plasticizing substance 

 if it is present without being split." The ATP 

 used in contraction is restored "almost as rapidly 

 as it is broken down by transphosphorylation of 

 phosphagens." 



Since the phosphorylization of ATP is the main 

 stage in the energy-prox-iding reaction in the 

 muscle, it is of interest to know the splitting 

 capacity of this compound in the adductor muscles. 

 Investigation of this problem by Lajtha (1948) 

 showed that the phosphatase activity is much 

 lower in bivah'e muscles {Mytilun and Pinna) 

 than in rabbit muscle. Lajtha suggests that this 

 is correlated with the slow working of the adductor 

 muscle, which does not require the quick energy 

 changes needed in the more rapidly functioning 

 muscles of vertebrates and insects. 



Chemical changes in the adductor muscle of the 

 oyster {C. commercialis) were studied by Hum- 

 phrey (1944, 1946, 1949, 1950), who demonstrated 

 the presence of arginine pliosphate and of several 

 phosphorylated breakdown compounds of glyco- 

 gen. The glycogen can be synthesized in both 

 parts of the muscle from glucose- 1 -phosphate, but 

 synthesis is more readily effected in the translucent 

 portion. 



In the glycolysis of the oyster muscle the glyco- 

 gen breaks down in the presence of added potas- 

 sium, magnesium, and DPN (diphosphopyridine- 

 nucleotide) and yields a mixture of pyruvic and 

 lactic acids (Humphrey, 1949). The glycolytic 

 ability of the adductor muscle of the oyster is 

 several hundred times less powerful than that of 

 rabbit muscle. 



Studies of the glycolysis in extracts of the 

 adductor muscle of C. commercialis (Humphrey, 

 1944) disclosed three essential facts: (1) phospliate, 

 potassium, magnesium or manganese, and DPN 

 are the essential parts of the system resulting in 

 the production of acid; (2) lactic and p.\Tuvic acids 

 are produced simultaneously; and (3) acid produc- 

 tion is inhibited by fluoride and iodoacetate. The 

 glycolysis in oysters and other invertebrates still 

 is not well understood, particularly witli respect 

 to the metabolism of pyruvate by oj-ster muscles. 



The ATP present in the adductor muscle has a 



definite relationship to glycolysis. The amount of 

 ATP in the muscle decreases when oysters are left 

 out of water. From this observation Humphrey 

 advances the hypothesis that the breakdown of 

 glycogen provides the enei'gy for the muscle to 

 resist the pull of the ligament. He thinks that the 

 regeneration of ATP proceeds through glycolj^sis, 

 wiiicii continues under both aerobic and anaerobic 

 conditions. Both conclusions require further cor- 

 roboration. 



NORMAL SHELL MOVEMENTS 



Studies of shell movements can give valuable 

 information regarding the physiological state of 

 the oyster and its reactions to the changes of 

 environment. Tlie only type of motion that can 

 be performed by an adult oyster consists of two 

 distinct components: the contractions of the 

 adductor muscle that bring the opposing valves 

 together and may completely seal off the soft parts 

 of the oyster, and tlie springlike action of the 

 ligament that pushes the valves apart during the 

 periods of relaxation. The purely mechanical 

 action of tlie ligament is counteracted by the 

 tonus of the muscle, which retains a certain degree 

 of elasticity even in the state of maximum stretch- 

 ing. If the muscle is cut off at the maximum 

 gaping, the valves are pushed farther apart by the 

 elastic force of the ligament. 



METHOD OF RECORDING 



Oysters selected for long-term observation (sev- 

 eral weeks or months) should be free of boring 

 algae and animals. The surface of the shell is 

 scrubbed with a metal brush, washed, and dried. 

 The left valve is embedded in a rapidly setting 

 mixtm-e of cement, sand, and unslacked lime in 

 proportion 1:2:1. Care should be exercised to 

 keep the edges of the valves free of cement mixture 

 and to wipe out and wash with sea water all excess 

 material. Mounted oysters are left in the air at 

 room temperature for 12 to 24 hours. 



A small metal loop cut from a paper clip may be 

 used to attach strmgs which lead to a recording 

 lever. The two arms of the U-clip are bent 

 horizontally, and the loop is placed on the clean, 

 dry surface of the right valve and sealed in a 

 vertical position by a few drops of iiot colophonium 

 cement. For recording the up and down move- 

 ments of a valve iieart and muscle levers available 

 at scientific supply houses can be used. Adequate 

 levers can be made of strips of appropriate length 

 cut from a sheet of plastic and mounted on pivots 



168 



FISH AND WILDLIFE SERVICE 



