894 



7. MERCURIALS 



but will not restore the respiration once it is inhibited; i.e., the surface- 

 bound Hg++ is available to the cysteine, but penetration of the amino acid 

 into the cells is inadequate to remove the Hg++ responsible for reducing 

 the respiration. 



Uptake of Hg++ by Diaphragm Muscle 



Logarithmic plots of Hg++ uptake with different initial concentrations 

 in the medium are shown in Fig. 7-38. There appears to be two components, 

 a fast phase with a half-time of 12 min and a slow phase with a half-time 

 of around 60 min. The uptake essentially ceases after 20-30 min at low 



Fig. 7-38. The uptake of Hg++ by rat diaphragm, 



at pH 7.4 and 38°, with time, as determined by the 



Hg++ remaining in the medium. (From Demis and 



Rothstein, 1955.) 



initial concentrations. It was assumed that the fast phase corresponds to 

 the diffusion of Hg++ into the extracellular space and binding to the plasma 

 membranes, the slow phase to the penetration into the cells. The time re- 

 lations point to a correlation between the membrane binding and the inhi- 

 bition of glucose uptake, and between penetration and respiratory kihi- 

 bition. 



