DUGALD E. S. BROWN 87 



and salt concentration l)y numerous investigators (13) showed that in 

 many ways the responses of these fibers resembled those of intact muscle. 

 The chief obstacle to quantitative studies, however, was the irreversibility 

 of the contraction. This obstacle has been largely removed, first by the 

 discovery of a relaxing factor (14) and later by the discovery that re- 

 laxation could be brought about by the addition of creatine phosphate 

 (CP) (15), phospho-enol pvruvate (PEPj (16) and carnosine phosphate 

 (17). 



In the course of studies of contractions that were reversil)le by these 

 agents, fiber preparations were made which exhibited various degrees of 

 contractile activity. Of especial interest was the evidence that prolonged 

 extraction of the glycerated fibers caused the disappearance of the relaxing 

 action of CP, which action could be restored by the addition of ATP- 

 creatine transphorylase to the fiber (18). 



A most important i)roperty of the glycerated fibers is that, under 

 suitable conditions, auto-oscillations occur (19, 20). In the presence of 

 ATP, Alg, and either CP or PEP, these fibers break into an oscillatory 

 contraction when allowed to develop tension against a torsion lever loaded 

 with a sufficient mass l)ut they fail to do so when the mass is removed. The 

 fact that the lever may be driven at a rate such that the oscillations 

 exceed the free period of the lever indicates that the alternate stretching 

 and releasing of the fiber by the loaded lever affects the capacity of the 

 fiber to develop tension. Such oscillations are a normal occurrence in the 

 flight muscle of certain insects, a fact which gives some confidence that 

 the glycerated fiber may be more than a model of the contractile system 

 and, in fact, has properties very similar to those in living muscle. 



In studies on contractions, a highly critical factor is the preparation of 

 the fibers. Lorand's method involves preparation in 50% glycerol and 

 storage for four weeks, then extraction in 0.10 m KCL, 0.01 m Xa2HP04 — 

 NaH,P04 at pH 7.0, 4 mM MgCU, 4 niM ATP and 10 niM phospho-enol 

 pyruvate (21). The resulting fiber develops a sustained contraction on 

 immersion in the testing solution, relaxes on the addition of PEP and is 

 contracted again on the addition of Ca++. In our laboratories, ]\Iarcus 

 Goodall prepared what he terms 'A' fibers in a different extraction medium. 

 These were prepared by placing the muscle in a solution of 50% glycerol, 

 5 mM histidine buffer at pH 6.8, and 2 niM NaCN for a period of two 

 to four weeks. The primary characteristic of Goodall's fiber is that on 

 immersion in the reaction mixture of pH 5.6 at 20°C the fibers contract, 

 l)ut then fully relax. Sul)sequently these will be referred to as n3 fibers. 



Tension and pH. In a series of studies with the nS fibers, tension 

 development as a function of pH, ATP, CP, temperature and pressure 

 was investigated (22, 2). The central phenomenon turns out to be the pH 



