K:Cl cotransport: emerging molecular aspects of a ouabain-resistant, volume-responsive transport system in red blood cells.

Erythrocytes from teleosts to mammals, like man, possess a ouabain-resistant K flux component which is Cl-dependent and activated upon suspension of the cells into hyposmotic media. This volume-responsive K:Cl cotransporter may be synonymous with a Cl-dependent K pathway stimulated by chemical interventions such as SH group (thiol) alkylation or oxidation at cytoplasmic sites of the membrane. Based on a comparison of the response of the two activity expressions of probably the same molecule to ionic and metabolic perturbations a molecular model is proposed accommodating K:Cl flux activities under a variety of stimulatory and inhibitory influences. Physiologically, this pathway may be involved in the maturational cell volume reduction occurring between the stages of reticulocytes and the final erythrocytes as well as corresponsible for the expression of the low K steady state of certain animal red blood cells. The pathophysiological potential of this K:Cl transporter lies in the fact that, when activated, red blood cells dehydrate through K:Cl loss.