Biological Aspects of Active Chloride Transport 



C. ADRIAN M. HOGBEN 



National Heart Institute, National Institutes of Health, 

 Bet he s da, M.aryland 



A COMBINATION OF CIRCUMSTANCES, particularly advances in neuro- 

 muscular physiology, have reinforced an impression that movement 

 of chloride through animal cell membranes is a passive phenomenon. This essay 

 is a brief for a better appreciation of the active transport of chloride. 



Because secretion of chloride by the stomach is especially well suited to 

 quantitative study, the clearly demonstrated active transport of chloride by 

 the gastric epithelium will receive disproportionate attention. In this instance, 

 active chloride transport is intimately linked to active transport of hydrogen 

 ion. The consequent attention given to the mechanism of hydrogen ion secre- 

 tion will be limited to its relevance to chloride transport and it does not do 

 justice to an accentuated interest in this problem reflected in several recent 

 reviews (5, 23, 41, 82). 



In this review it is not intended to offer a sequence of well-ordered conclu- 

 sions. Rather, the object has been to emphasize several of the provocative 

 aspects of univalent anion movement across animal cell membranes. 



USAGE OF ACTIVE TRANSPORT 



A concept fundamental to an understanding of factors governing movement 

 into and out of cells is the slowly evolving distinction between passive penetra- 

 tion and active transfer. Biologists generally recognize that movement through 

 living membranes cannot be simply described in terms of a static barrier be- 

 tween two solutions but that passage often involves transfer of energy from the 

 cells so that material is lifted uphill. There is less agreement on how to use the 

 words needed to analyze the several factors involved, though perhaps the gen- 

 eral formulation of Hober (42, pp. 523-529) is representative of earlier think- 

 ing. The choice of terms and the manner in which we use them is influenced 

 by the questions immediately before us. When we are concerned with ionic 

 movements which determine electrical phenomena, a more rigid definition of 

 passive penetration will be sought. When the step involving transfer of met- 

 abolic energy to a specific ion is the point of emphasis, we need to clarify usage 

 of active transfer. 



For our present purposes passive diffusion and active transport will be de- 



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