VARIATION OF INTRACELLULAR INHIBITION WITH pH 



723 



branes of the cells. Other evidence comes from the work of Simon and 

 Beevers (1952) and this will be discussed in later sections. Finally, similar 

 results have often been obtained in studies on drugs, most of which has 

 been reviewed by Albert (1952). A particularly conclusive study on the bar- 

 biturates has been reported recently (Hardmanef o/., 1959) and it was dem- 

 onstrated that the depressant action upon isolated cardiac tissue is pro- 

 portional to the concentration of the uncharged form, the ions not exerting 

 any effects. 



100 



Fig. 14-19. Variations of the inhibition of plant tissue respiration by malonate 

 at difierent pHs. Curve A: tomato stem slices (Link, et al., 1952). Curve B: maize 

 roots (Beevers, 1952). Curve Cj: rhubarb leaves — malonate = 6.8 mM (Morrison, 

 1950). Curve Cj: rhubarb leaves — malonate = 34 mil/ (Morrison, 1950). Curve 

 D: barley roots (Laties, 1949). Curve E: spinach leaves (Bonner and Wildman, 

 1946). curve F: Avena coleoptile (Cooil, 1952). curve G: carrot root slices — 136 

 min after cutting (Hanly et al., 1952). 



It is thus established that the uncharged forms of weak acids and bases 

 penetrate into cells more readily than do the ionic forms. The question now 

 arises as to whether the ionic forms penetrate at all or are of any signifi- 

 cance in the actions of these substances. The answer to this question is 

 not so easily given. In some cases the results conform closely to the behav- 

 ior to be expected if only the neutral form penetrates and the ionic form 



