COUPLING OF ION FLOWS IN CELL SUSPENSION SYSTEMS*

Abstract

A valid test for cotransport between solutes is a demonstration that the degree of coupling between all coupled solute flows concerned, q defined in terms of Irreversible Thermodynamics, is sufficiently close to unity. The usual method to determine q kinetically by pulses and responses of flows can not simply be applied to rheogenic ion flows, as electrical potential difference changes due to the pulses can hardly be avoided. If, however, the ion flows are all electrically silent, changes in electrical potential difference (PD.) should not interfere with the determination of q. This holds for the furosemide-sensitive fluxes of Na+, K+, and Cl- in Ehrlich cells, each of which could be shown to be unaffected by a change in electrical PD and vice versa. Hence the q values could be determined for any pair of the three ion flows concerned and none differed significantly from unity. These results appear to indicate a furosemide-sensitive, electrically silent ternary symport mechanism for Na+, K+, Cl- with the stoichiometry 1:1:2, which is active but does not utilize ATP. It is assumed to function as a very efficient regulator of cellular volume and may be identical with other previously described binary symport systems.