94 



INFLUENCE OF TEMPERATURE ON BIOLOGICAL SYSTEMS 



tion and shortening begins but it is soon terminated by the deactivation 

 process. Although presenting experimental difficulties due to the speed of 

 events, the twitch presents the ideal situation for investigating the acti- 

 vator system in relation to the formation of the active contractile complex 

 necessary for the development of tension. 



Pressure Contracture. When striated muscle (retractor penis of turtle) 

 is hydrostatically compressed to above 4,000 psi, tension develops, reaching 

 a maximum which is sustained until the pressure is removed (fig. 5) (24, 

 25, 2 ) . The development of tension begins immediately on compression, 

 but after an abrupt decompression the contraction continues for a brief 

 period before relaxation ensues. The contraction is not accompanied by a 



272 ATM. 



Fig. 5. The pressure contrac- 

 ture of retractor penis of turtle 

 at 10°C, employing abrupt com- 

 pression and decompression with 

 4,000 psi. A: control twitch. B: 

 twitch superimposed on contrac- 

 ture at 2,000 psi. In remaining 

 myograms the pressure is ap- 

 plied abruptly and as abruptly 

 removed progressively earlier in 

 the contraction. 



propagated action potential and in its main characteristics satisfies Gas- 

 ser's critieria (26) for a contracture. 



The maximum contracture tension increases with pressure along an S- 

 shaped curve, reaching an upper limit at pressures exceeding 8,000 psi 

 equal to the maximum tetanus tension. The relation is similar to that ob- 

 tained on the glycerated fiber (fig. 3.4), and when subjected to the same 

 analysis logio [y/(l — y)] varies linearly with pressure, with a AV of —350 

 cc/mole (fig. ZB, 4C-2). As yet, a decrease in tension in the contracture at 

 higher i^ressures with a resulting optimum in the tension curve has not 

 been observed at pressures up to 12,000 psi. 



The contracture also resembles the glycerated fiber in that the minimum 

 pressure necessary to produce the contractures is influenced by chemical 

 agents, in this instance the concentrations of K + , Ca++ and CI" in the 

 bath. With 4 mM K+ and 2 niM Ca++ the contracture begins at 500 to 

 1,000 psi, with 2 niM K+ and 2 mM Ca + + at 3,000 to 3,500 psi, while at 



