The kinetics of anion equilibrium exchange across the red blood cell membrane as measured by means of 35S thiocyanate

Abstract

Up to a SCN- concentration of about 110 mM, the concentration dependence of SCN- equilibrium exchange in human red cell ghosts can be represented by the superimposition of two flux components. One component shows saturation kinetics, the other does not. The saturable component has an activation enthalpy of 105 kJ/mole, exhibits a trans acceleration by Cl- and can be inhibited by H2DIDS. The nonsaturable component has a much lower activation enthalpy of 33 kJ/mole, is slightly reduced in trans acceleration experiments with Cl- and insensitive to H2DIDS but susceptible to inhibition by phloretin. At SCN- concentrations exceeding 110 mM, the saturable component undergoes irreversible self inhibition while the nonsaturable component remains unaltered. The half saturation concentration of the saturable flux component increases with decreasing pH from 3.0 mM at pH 7.4 to 13.3 mM at pH 6.0. Over this pH range, the maximal flux is only slightly increased from 19 x 10(-12) to 22 x 10(-12) moles x cm-2 x sec-1. The nonsaturable flux component also increases slightly. In accordance with previous observations of Wieth (J. Physiol. (London) 207:563-580, 1970), we find that SCN- increases K+ and Na+ permeability. The induced cation-permeability is considerably smaller than the SCN- exchange and the latter does not show the paradoxical temperature dependence that is known to pertain to the former.