TEMPERATURE-PRESSURE RELATION 

 IN MUSCULAR CONTRACTION 



DuGALD E. S. Brown, Department of Zoology, 

 University of Michigan, Ann Ar'bor, Michigan 



-HE PHYSICO-CHEMICAL ANALYSIS of iiiuscular Contraction in relation to 

 temperature and pressure has been limited by the difficulty of defining 

 shortening and tension in terms of identifiable rate processes and equilib- 

 brium changes. In regard to temperature, investigators have been in the 

 perplexing position of being unable to interpret the effects of this factor on 

 any event in contraction in terms of either a heat of reaction, AH, or a heat 

 of activation, AH*, or even a net result of both. The same situation exists 

 with respect to the effects of pressure and the volume change of reaction, 

 aV, or of activation, aV*. 



Recently in studies on myosin ATPase ( 1 ) and on the glycerated psoas 

 fiber of the rabbit (2) results have been obtained which offer a clue to a 

 rational interpretation of the action of temperature and pressure in con- 

 traction. These results in consequence open the way to a useful comparison 

 of the values of the thermodynamic and rate constants as a step toward the 

 identification of reactions common to myosin ATPase and contractile 

 events in the glycerated fiber and intact muscle. The extensive investi- 

 gations of Johnson, Eyring and colleagues (3) on a variety of biochemical 

 and cellular processes have clearly shown the usefulness of such a method 

 in the analysis of cellular events. Although a similar approach toward such 

 an analysis of contraction must proceed at present on somewhat limited 

 evidence, its presentation at this time may serve to stimulate critical 

 studies in a direction which appears to deserve further and more intensive 

 investigation. 



In considerations of contraction, the concept has developed that the 

 sustained tension in a tetanus or contracture may be pictured as a steady- 

 state condition involving the maintenance of the actomyosin in an active 

 contracted configuration at the expense of concomitant enzymatic and 

 other processes. Schematically the system may be described in formula (1) 

 p. 84. 



From the studies of Hill (4j on the sartorius of the frog and toad, in 

 which a quick stretch is interposed at various times after stimulation, it 

 is evident that the formation of the relaxed activated unit AMa,-^ begins in 

 the latent period, and the fully 'active state' is reached in the initial one- 



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