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



JV. Myant. Discrimination between sodium and potassium need not depend on speci- 

 ficity of pores. It might be due to an intracellular reversible complex formed with 

 potassium but not sodium. 



J. F. Danielli. So far no intracellular complex has been found which is highly selective 

 for sodium or potassium. 



M. M. Swann. I should like to draw attention to the parallel which seems to exist 

 between active transport and the fertilization of an egg by a sperm. Fertilization is 

 a highly specific process of course, and there is little doubt that the sperm is drawn 

 passively through the egg membrane. I have also been struck by the fact that many 

 of the substances which have a powerful effect on active transport also affect fertiliza- 

 tion. Copper and lead, and most basic dyes, inhibit it; nicotine induces polyspermy. 

 Work that Rothschild and I have done suggests that one can actually put a figure on 

 the probability of a successful sperm-egg collision, and we are inclined to think of the 

 reaction in immunological terms. Would it help to think of active transport in these 

 terms ? 



J. F. Danielli. It is possible that the reason why there is a similarity between factors 

 influencing active transport and factors influencing fertilization is that in both cases 

 the phenomena are mediated by contractile proteins, as Goldacre (1952, Int. Rev. 

 Cytol. 1, 135-164) has suggested. There is probably a close relationship between the 

 factors conferring specificity in active transport and in immunological reactions. 

 I have previously suggested that adaptive active transport arises by a process analo- 

 gous to antibody formation (1954, Symp. Soc. exp. Biol., in press). Pauling has shown 

 that specific changes in proteins may be produced in artificial systems by small 

 molecules. This indicates that the process postulated is feasible. 



B. F. Folkes. Has Professor Danielli considered the energetic requirements of the 

 uptake of KC1 by cells? In plant roots, Robertson found that for an increase of 

 oxygen uptake of one molecule, four molecules of KC1 were taken up. Allowing for 

 back diffusion this suggests that 1 high-energy phosphate bond is used for the uptake 

 of one molecule of NaCl. Current theories suggest that many more ATP molecules 

 are necessary for the contraction of one protein molecule. Does this not rule out the 

 idea of contractile proteins in active transfer ? 



J. F. Danielli. No. The theory of active transfer of ions by protein contractions 

 depends upon a protein oscillating between two alternative configurations. In the 

 simplest case this will occur under thermal agitation, as in the dynamic equilibrium 

 between native and denatured trypsin studied by Anson and Mirsy. In such in- 

 stances the activation energy is low. If the activation energy for the change is high, 

 thermal agitation may be supplemented by chemical energy derived from acetyl- 

 choline or ATP. 



J. E. Harris. Are we confusing acetylcholine as a trigger with ATP as an energy 

 source ? The effect of acetylcholine on cilia is to produce a change in frequency of a 

 contractile process the energy of which is derived from other sources. Whiting and I 

 have found that acetylcholine has a similar effect on rhythmical contractions of 

 embryonic voluntary muscles in the myogenic stage. 



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