H. J. KOCH 



cholinesterase which is concerned in the active transport of ions. Even if cholin- 

 esterase is also present on the inner surface of the gill epithelium this will not help to 

 explain the effect of basic dyes on the outer surface of the gills; this inwardly- 

 situated cholinesterase would also be out of action in the last-mentioned experiment 

 because of the anti-cholinesterase effect of the injected basic dyes. 



INFLUENCE OF CLASSICAL INHIBITORS OF CHOLINESTERASE ON THE 

 ABSORPTION MECHANISM OF THE GILLS 



The foregoing interpretation of the action of basic dyes is corroborated by the effect 

 of classical inhibitors of cholinesterases such as eserine (physostigmine) and diiso- 

 propylfluorophosphate. Their inhibitory influence on salt transport is shown in 

 Figure 6. The inhibitory action of these substances is entirely reversible. 



20 minutes. 60 



100 



Figure 6. JVaCl absorption by a gill of the crab as 

 influenced by DFP (diisopropylfiuorophosphate) and 

 eserine (physostygmine). Upper curve: DFP added 

 first at io -3 m concentration, and later, in the absence 

 of effect, brought to 1 -g X io -3 m. DFP removed at 

 -DFP. Lower curve : eserine added at 1 o -3 M 

 concentration, and removed at -PS. {From Koch, 

 Evans and Schicks, 1954&.) 



Tetraethylpyrophosphate is generally considered to be an irreversible inhibitor of 

 the cholinesterases, and we also found (Koch, 1954) that its inhibition of salt 

 transport is irreversible after washing with water. Kirschner (1953) made a 

 similar observation on frog skin. However Wilson (1951, 1952) has shown that 

 the inhibition of cholinesterase with alkyl-phosphates is reversible under the 



22 



