The field of facilitated diffusion ■ Transport of sodium chloride through gills of crab 



H. Koch. Most of the experiments with DNP were carried out near pH 7, but those 

 carried out at other pH values also failed to indicate any effect. When injected into 

 the animal DNP proves to be an excellent inhibitor of active salt transport. 

 P. H. Tuft. Professor Koch says that the gills stain with basic dyes but that after 

 washing activity reappears although the gills are still stained. Is it the chitinous 

 cuticle which stains? 



H. Koch. We observed that the dye which becomes free in very low concentration 

 after the gill has been washed and replaced in 8 ml. NaCl is enough to inhibit activity 

 again after a short time. This seems to indicate that certain definite points of the 

 membrane must be occupied to obtain inhibition. This would fit in with the pore 

 hypothesis. 



R. J. Goldacre. A concentration of io~ 3 m neutral red, which you found to inhibit 

 active transport in Eriocheir gill, is near that which inhibits locomotion in Amoeba 

 proteus. When locomotion stops in Amoeba, active transport of neutral red stops also. 

 I was wondering whether the dyes in your experiments prevented contraction in the 

 cytoplasm, which might explain some of your results. 



H. Koch. Although the larger part of the gill membrane is covered with a chitinous 

 cuticle, it is quite possible that dyes interfere with movements in the cytoplasmic 

 membrane when reaching it at certain places. 



Is it possible that neutral red interferes with the movement of Amoeba by acting on 

 a cholinesterase in this animal? 



R. J. Goldacre. I have tested acetylcholine on Amoeba proteus over a wide range of 

 concentrations, and found no effect. 



P. H. Tuft. Does the calcium-ion concentration have any effect on Na or K uptake 

 by Eriocheir gills ? It is said that the failure of this crab to invade Norwegian rivers is 

 due to their low calcium concentration, and there is a connexion between calcium 

 and acetylcholine. 



H. Koch. The presence of calcium ions seems unnecessary for the active uptake of 

 Na or K, and does not influence this uptake seriously, as far as I can judge from 

 preliminary experiments. Perhaps Norwegian rivers also contain very little NaCl, 

 and this may be a limiting factor. Low temperature may also have an unfavourable 

 influence on the osmotic regulation and moulting of the crab. 



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