COXCEXTRATION-TIME CURVES FOR INHIBITION 



595 



of cells in a contractile tissue is quite variable ("Webb, 1956), indicative per- 

 haps of differences in membrane permeability, ionic distribution, and me- 

 tabolically-linked active transport. The metabolism of such preparations 

 is thus made up of contributions of varying degree from these different 

 types of cells. The rate at which an inhibitor produces a depression of 

 respiration in a tissue, for example, would also be composite in nature, 

 although here the time course of the effect would depend not only on the 

 variation but also on the true rate of inhibition. In addition to these fac- 

 tors, there is the further problem of the penetration of the inhibitor into 



2 



- 15 



- I 



- 0.5 



- 



LOG % 

 SURVIVORS 



10 20 

 TIME (MIN) 



30 



40 



50 



Fig. 12-36. Death rate curve for Colpidium exposed to 0.2 mM 

 HgCla. (From Peters, 1920.) 



the inner layers of the tissue. Certainly many inhibitors do not rapidly 

 reach the cells within a tissue or tissue slice when applied in the medium 

 bathing the preparation, and this would, of course, make the observed rate 

 deviate even more from the fundamental rate of inhibition in which one is 

 interested. 



CONCENTRATION-TIME CURVES FOR INHIBITION 



A common method of expressing inhibition kinetics has been to plot the 

 concentration of the inhibitor against the time required to produce a chosen 

 effect. These curves have often been fit by a general equation of the type: 



[(I) - {l)J,"[t - t„:j = C (1-2-89) 



where (I),„ is the minimal inhibitor concentration to produce the effect and 



