Factors affecting the activation and inactivation of KCl cotransport in 'young' human red cells.

KCl transport plays an important role in the control of 'young' red cell volume and hence MCHC. The activity of this pathway declines rapidly during maturation in vitro irrespective of whether the transporter is functioning or not. The presence of plasma retards the rate at which the transporter becomes cryptic; N-ethyl maleimide can restore transport activity. Low pH is more effective as an activator of the transporter than hypotonicity, suggesting that protons stimulate the transporter directly rather than via a change in cell volume.