H. J. KOCH 



influence of choline and other substances. Recently we were able to obtain also with 

 choline a reversal of the inhibition of salt transport by TEPP for the gills of Eriocheir 

 (Figure 7). All these inhibitors have an entirely similar effect on the absorption of 

 Na by the anal papillae of the larvae of Chironomus as illustrated by Figure 8. 



INFLUENCE OF CURARE 



It may be of special interest to notice that </-tubocurarine hydrochloride, which is 

 supposed to act selectively on neuromuscular transmission, is also quite an active 

 inhibitor of ion transport in the gills of Eriocheir. Tubocurarine is supposed to act 



-Tubocurarin*. 



(/ + Tubocurarine . 0716.10 M. 



20 MINUTES. 60 



eo 



TOO 



Figure 9. Influence of d-tubocurarine HCl on the 



JVaCl absorption of a gill of a crab. (Koch, 



Evans and Schicks, 19546.) 



not so much by inhibiting cholinesterase as by competing with acetyl choline for the 

 same receptor protein. This action seems to be partly reversible (Figure 9) . In certain 

 cases it has been shown that cholinesterase inhibitors affect the permeability of these 

 structures (Rothenberg, 1950). 



CONCLUSIONS 



The most suggestive fact which seems to emerge from what has been explained so 

 far is the importance of a cholinesterase as a component of the mechanism which 

 actively transports ions through the gill epithelium of the crab. Moreover a cholin- 

 esterase seems to be also an important part of the mechanism for the active transport 

 of Na in the anal papillae of an insect, the larva of Chironomus plumosus. 



Now it has been shown recently by Kirschner (1953) that an enzyme which be- 

 longs to the same group is a part of the mechanism for the active transport of Na in 



24 



