Steady-state and transient membrane potentials in human red cells determined by protonophore-mediated pH changes.

Protonophores have been used frequently to determine changes in membrane potential in suspensions of red cells, since such changes are reflected by changes in extracellular pH, due to proton and consequently protonophore reequilibration. In a previous paper (Bennekou, P. 1988, J. Membrane Biol. 102:225-234) a kinetic model for the translocation of a protonophore, CCCP, across the human red cell membrane was established. This model accounts for the protonophore reequilibration following abrupt changes in membrane potential. In this paper the limitations of the method with regard to the estimation of transient membrane potentials are examined, using the transport model to simulate changes in extracellular pH in response to noninstantaneous changes in membrane potential. The temperature and time resolution calculated from the model are reported. Furthermore, it is shown that the transport model established for CCCP is valid for another protonophore, TCS, thus indicating the general validity of the transport scheme for the entire class of protonophores.