Ion Transport and Short-Circuit Technique

Abstract

Publisher Summary This chapter discusses the use of the well known short-circuit technique for studying active and passive ion transport. This technique has been used primarily for deciding between passive and active ion transport and for the determination of the effect of agents and procedures on the rate of active ion transport of the type, in which the net active transport can be equated to the net transport of charge. Many workers seem to assume that, during short-circuiting, the membrane possessing the active transport mechanism is short-circuited. Most of the workers in this field use the simple Ussing-Zerahn equivalent circuit and imply that, it is adequate to represent complex tissues. It is generally accepted that if the transport of an ion is essentially zero under short-circuit conditions, then the conclusion is warranted that the ion in question is passive. There is also considerable misunderstanding among workers using the simple Ussing-Zerahn circuit concerning the relationship between the conductance of this circuit and that of the actual tissue. The chapter describes that (1) if all the ion transports are exclusively via conductive pathways, the criteria for passive ion transport of the Ussing are valid for both single- and double-membrane models, but (2) if there are nonconductive pathways for ions that cannot be represented by an equivalent-circuit conductive pathway, then the accepted criteria for passive transport are not valid. The chapter discusses conductive pathways for all the ions involved, and the fallacy of using the criteria for systems in which there are nonconductive pathways.