K-CL COTRANSPORT IN RED-CELLS OF TRANSGENIC MICE EXPRESSING HIGH-LEVELS OF HUMAN HEMOGLOBIN-S

K:Cl cotransport is involved in generating dense red blood cells (RBCs ) in homozygotes for HbS (SS), We report on the properties of this tra nsport system in RBCs from control and transgenic mice expressing high levels of human alpha(H) and beta(S) chains, Unlike human SS RBCs, mo use RBCs incubated in isotonic media exhibited a Cl--dependent K+ effl ux and therefore have a different set-point for activation, This basal efflux was slightly stimulated by cell swelling to values five times smaller than that in human SS cells; in addition, the delay time for a ctivation was shorter in transgenic than in control mice, but fourfold longer than that of human SS cells, These properties cast doubt on th e physiological impact of the mouse K:Cl cotransporter on RBC volume r egulation in the mouse and suggest that there are intrinsic difference s between the human K:Cl cotransporter and the putative transporter in mice. (C) 1997 Wiley-Liss, Inc.