RESPIRATION 879 



°o Changes from Hg++ at: 



substrate seems to be real since it was consistently obtained. The inhibition 

 with pyruvate + malate as substrates and Hg++ at 0.01 vcvM is about 50% 

 at 10 min and then increases more slowly until it is 100% at 60 min. The 

 figures in the tabulation are mean inhibitions over the 60 min period and 

 even at 0.01 milf the activity was almost all lost in aU cases by 60 min. 



RESPIRATION 



The effects of the mercurials on the 0., uptake of tissues vary considerably 

 and depend on the mercurial used, the substrate, the pH, the species, and 

 many other factors (Table 7-17). One factor about which little is known, 

 but which could be very important, is the thickness of the tissue when the 

 preparation is a strip, section, or slice, inasmuch as the mercurial possibly 

 does not penetrate equally throughout but acts primarily on the outer 

 layers of cells. Cascarano and Zweifach (1962) examined rat diaphragm 

 after exposure to Hg+"^ by determining the ability of the tissue to reduce 

 a tetrazolium dye, and found that only a well-defined band of surface fibers 

 had lost the ability, the central portions retaining activity. Measurements 

 of respiratory inhibition in such cases do not provide true values (see page 

 1-479); in the extreme case the inhibition may relate only to the fraction 

 of the tissue affected, and progressively developing inhibition may exhibit 

 time relations dependent only on the rate of penetration through the tissue. 

 This would apply not only to respiration, of course, but to all measurements, 

 metabolic or functional, made on all intact tissues. Failure to reach all of 

 the cells equally must be one reason for the low degree of inhibition often 

 observed, lower than would be predicted from the effects on glycolysis, 

 the cycle, and the enzymes involved. 



One notes several examples wherein respiration is stimulated by the mer- 

 curials, more often at low concentration but in one instance, yeast respir- 

 ing endogenously (Shacter, 1953), the stimulation appears only at high 

 concentrations of 1-2 vaM. There are other reports of stimulation not in- 

 cluded in the table. For example, Gremels (1929) found that when mersalyl 

 induces diuresis in a heart-lung-kidney preparation, the kidney respiration 



