Countertransport in Human Red Blood Cells

Abstract

The term counterflow designates a special case of interactions between simultaneous movements of two different substrates of the same carrier transport system. Its occurence has been demonstrated in a number of cases where saturation kinetics and other evidence suggested the participation of carriers in transport processes. In general, the term is used to designate movement of one substrate S out of equilibrium (i.e. uphill), induced and energized by the simultaneous movement of a second substrate R down its concentration gradient. Under these conditions the direction of the induced flow is opposite to that of the inducing substrate. This effect led to the introduction of the term ‘countertransport’ or ‘counterflow’. However, the interaction is not restricted to this special case but also is observed when the substate S moves with finite rate in the same direction as R. Then the interaction leads to slowing of the movement of S.