480 9. INHIBITION IN CELLS AND TISSUES 



tissue to bind the arsenical is only 0.01% (0.1 mg arsenical per gram of 

 tissue) and 100 mg of tissue are present, 0.01 mg of the inhibitor can be 

 bound maximally, and this is approximately twice as much as is present. 

 This factor can then be easily of importance, particularly with the more 

 potent inhibitors. The kinetics in such cases will be similar to those for 

 mutual depletion systems and the calculation of inhibition constants by 

 the use of the classic plotting techniques can lead to very erroneous values. 

 The uncoupling agent, 2,4-dinitrophenol, is not a substance that is 

 strongly bound to cellular material, and yet when different cell densities 

 of yeast suspension were equilibrated with 0.49 milf 2,4-dinitrophenol, the 

 amount taken up per cell decreased with increasing density (Kiesow, 1959). 

 The falling off was particularly evident when the total cell volume reached 

 100 mm^ and it was calculated that over half the uncoupler could be de- 

 pleted from the medium. Inasmuch as this uptake was readily reversible 

 and dead cells took up very little 2,4-dinitrophenol, it would seem that 

 binding to the cell components is not the reason for the accumulation in 

 the yeast cells. If the concentration of 2,4-dinitrophenol had been lower, 

 as it usually is in uncoupling experimen~ts, the depletion from the medium 

 would have been more marked. Thus the factor of reduction in the inhibitor 

 concentration must be at least considered in most work done with living 

 cells or tissues. 



The Functional State of the Tissue 



It is well known that both the rate and pattern of metabolism vary 

 with the functional activity of a cell or tissue. The problem often arises 

 as to the state of a tissue slice and if results with inhibitors on them can 

 be applied to the intact functioning tissue. Difficulties arise even with 

 more intact tissue preparations, such as isolated atria, ventricular strips, 

 or intestinal segments, unless the contractility can be measured simultan- 

 eously with the metabolism or in some manner correlated with it. Kidney 

 slices can perform transport work under appropriate conditions but in 

 most cases their activity is far below that of intact renal tissue. The re- 

 lation between function and metabolism in tissue slices has been studied 

 most carefully on the brain (Mcllwain, 1959), where electrical stimulation 

 of the tissue in respirometer flasks results not only in a new pattern of 

 metabolism but alters the sensitivity of the metabolism to various drugs 

 and inhibitors. lodoacetate, fluoride, and malonate depress stimulated 

 brain slices more readily than resting slices; 10 mM malonate has no effect 

 on the respiration of resting slices but 1-2 mM malonate is inhibitory to the 

 extent of 12-40% when electrical stimulation is induced. It is quite probable 

 that similar behavior would be demonstrated by other tissues. Designation 

 of the usual tissue slice as resting is perhaps not always justified. What is 

 the functional state, for example, of a myocardial slice in a Warburg vessel? 



