DO HBSS ERYTHROCYTES LOSE KCL IN PHYSIOLOGICAL CONDITIONS

KCl cotransporter activity in sickle (HbSS) red blood cells (RBCs) was measured in cells suspended in 'simple' physiological saline, saline augmented with inorganic salts, and autologous plasma, Our results sho wed that the transporter was only functioning at 20% of the level of c ells in saline when cells were resuspended in autologous plasma, Kinet ic analysis of the data showed that plasma decreased both V-max and K- m for K+ of the transporter. The plasma factor(s) responsible was heat -stable and dialysable (i.e. size < 10 kD). Adding magnesium, calcium, inorganic phosphate or bicarbonate to 'simple' saline to mimic the ef fect of plasma revealed that Mg2+ and Ca2+ had no significant effect a t physiological concentrations. P-i was not effective at 1.1 mM, but d id inhibit significantly (42+/-2%) at 5.6 mM. HCO3- had a major inhibi tory effect on K+ influx when added to saline, and was identified as t he principal candidate for the plasma effect. We suggest bicarbonate m ay play a significant role in modifying KCl cotransport, and hence HbS S cell volume in vivo, It acts by altering the set point of the transp orter via the signalling systems involved in its regulation.