Choline sterase and transport of sodium chloride through gills of Eriocheir sinensis (M.Edw.) 



During the period of treatment with the C0 2 and air mixture, there is a close 

 correspondence between the estimates of outflux obtained by the tracer and by the 

 conductivity methods, so that it seems rather probable that the increase in conduc- 

 tivity is fully accounted for by the outflow of NaCl. It is also clear that the net intake 

 represents the difference between a considerable outflux and a normally still more 

 considerable influx of Na. 



The inhibiting effect of C0 2 on the ion-absorption mechanism has been described 

 by Ussing for the frog's skin, and we have found that the same substance is also a 

 very strong inhibitor for the sodium uptake of the anal papillae of the larvae of 

 Diptera. 



136,653 



leulated point. L_ ; 



60 MINUTE S. lOO 



120 



16O 180 



Figure 2. The reversible inhibition by C0 2 (1 part in 12 of 



air) of the net uptake of NaCl (as determined by conductivity). 



Simultaneously the outflux of previously absorbed 22 J\fa is 



measured. (From Koch, Evans and Schicks, 1954a.) 



In the complete absence of oxygen, only outflux takes place. The necessity of free 

 oxygen for ion uptake in Chironomus larvae has been shown already by Hers (1942). 



Classical inhibitors of cytochrome oxidase (KCN, NaN 3 ), previously used by 

 Krogh (1939) on whole Eriocheir, as well as Na 2 S, have a strong depressing effect on. 

 ion absorption : the reversibility of their influence is easy to show on isolated gilli 

 preparations. 



It is tempting to imagine that the need for cytochrome oxidase, so well established 

 for wheat roots by Lundegardh (1951), is general for all ion-absorbing systems. 

 However this enzyme seems to play no part in the ion-absorbing mechanism of the 

 anal papillae of Chironomus larvae (H. Koch and Schicks, unpublished). 



While trying to elucidate the importance of the cytochrome-cytochrome oxidase 

 system for ion absorption in the gills of the crab, it seemed interesting to investigate 

 what would happen in the presence of a substance able to open a new pathway for 



17 



