Originally published in Acta Physiol. Scand. 2, 171 (1940). 



44. RATE OF PENETRATION OF PHOSPHATE INTO 



MUSCLE CELLS 



G. Hevesy and O. Rebbe. 



From the Institute of theoretical Physics and the Zoophysiological Laboratory, 



University of Copenhagen 



Certain constituents of the voluntary muscle are able to diffuse out 

 of the muscle into a surrounding saline and can also diffuse into the 

 muscle if previously dissolved in the saline in a sufficiently high con- 

 centration. There exists, in such cases, a given concentration of the 

 substance in saline which will be in equilibrium with the tissue. This 

 critical concentration provides a measure for the concentration of the 

 substance in the tissue — or rather in such part of the tissue as is con- 

 cerned in the diffusion. M. G. Eggleton (1933) carried out such ex- 

 periments(i) in respect of phosphate exchange by immersing in Ringer's 

 fluid an excised frog muscle at 2° for a few hours and found that in the 

 resting muscle 20—30 per cent of the muscle water, corresponding to 

 about 16—24 per cent of the weight of the fresh muscle, was involved in 

 the diffusion system. Since 8 — 16 per cent of the weight of the gastroc- 

 nemius is composed of the interspaces into which the phosphate of 

 Ringer's fluid will easily penetrate, the result mentioned above suggests 

 either that phosphate can diffuse only into a certain fraction of the 

 tissue beyond the extracellular volume or else that phosphate ions can 

 penetrate only slowly into the muscle cells. That the latter alternative 

 is more likely follows from the fact that no perceptible decrease in the 

 total acid soluble phosphate content of muscles is apparent after fatigue, 

 though a very perceptible increase in the inorganic P content of such 

 muscles takes place. If the cell membranes were easily permeable to 

 phosphate ions, a part of this excess phosphate should soon leak out 

 into the plasma. 



The application of the method of isotopic indicators permits us to 

 follow the path of the labelled phosphate ions introduced into the cir- 

 culation by making use of radioactive measurements. Due to the great 

 sensitivity of this method it is possible to determine even very small 

 amounts of labelled phosphate ions which migrate under strictly physio- 

 logical conditions into the muscle cells during a few hours or less. 



(1^ Comp. also Stella (1928). 



