The kinetics of the Cl-pH equilibration in human red blood cells

If erythrocytes were transferred into solutions of different ionic composition, they changed the inner pH and chloride concentration until reaching a new quasi-equilibrium state (C-State). Electrochemical measurements were performed to follow the kinetics of this adaption and to answer the question whether the time constant of unidirectional chloride flux or time constant of chloride net flux is responsible for this process. It was found that the kinetics depend strongly on the kind and the concentration of the buffer system used. In unbuffered solutions, a new Cl-pH-equilibrium is reached very fast and proceeds by the Cl-/HCO-3-exchange. If Tris or phosphate buffer were used, this process had a time constant of about 10(-3) S-1 and was mainly realised by a Cl-/OH-exchange or Cl-H+-cotransport. If the suspension contained phosphate, an overshoot of pH took place. The reason for this behavior is the additional exchange of Cl- for HPO2-(4) + H+.