Active Transport and Membrane Expansion- 

 Contraction Cycles 



R. J. GOLDACRE 



Chester Beatty Research Institute, Institute of Cancer Research, 

 Royal Cancer Hospital, London, England 



I. Introduction 



That a rhythmically expanding and contracting surface might, by 

 adsorbing and subsequently desorbing yarious substances, be a mechanism 

 used by the cell to concentrate substances ^yithin it \yas suggested by 

 Goldacre and Lorch [4] and Goldacre [5]. Chemical model experiments 

 sho\yed that substances could indeed be concentrated in this \yay, and 

 tests \yith amoebae in yarious dye solutions, such as neutral red, methylene 

 blue and other basic dyes, indicated that dyes accumulated at that part of 

 the cell \yhere contraction took place, namely the rear end or "tail". This 

 accumulation \yas sho\yn not to be due to a pH difference bet\yeen the 

 amoeba's tail and the external medium, for it occurred equally well in 

 media from pH 4 to 8 [6]. Further support was giyen by Prescott [i i], who 

 not only confirmed the original obseryations but, by preyenting plasmagel 

 contraction by conyerting it all into plasmasol by the application of a 

 hydrostatic pressure of seyeral hundred atmospheres, preyented the 

 accumulation of neutral red by the cell which, howeyer, began to accumu- 

 late it when the pressure was released and plasmagel contractions were 

 restored. 



The contractile protein hypothesis has been modified and extended by 

 Danielli [3] who suggested that protein chains lying on the outside of the 

 cell membrane with adsorbed substances on them might actually be pulled 

 inside through a micropore by an internal contraction ; he further showed 

 that, on the assumption that ATP proyided the energy for the contraction 

 (which ATP is known to cause when injected into amoebae [4] and slime 

 moulds [13]) the distribution of phosphatases in yarious secretory tissues 

 is appropriate to the direction of secretion. 



In amoebae, the rhythmic contraction-expansion cycle is obyious 

 microscopically, but other cells, such as red cells, which do not reyeal 

 marked rhythmic moyements eyen in time-lapse cinematography, haye 

 actiye transport mechanisms. It is interesting in this connection that a 



