Analysis of Ca2+-induced K+-transport of human erythrocytes in propionate media.

A method is described which allows studying specific cation transport pathways of the cell membranes by converting ion fluxes into volume changes. Lipophilic weak electrolytes, such as propionate, rapidly penetrate the cell membranes in their undissociated acid from but not as negatively charged ions. When human red cells are incubated in isoosmotic K-propionate media an intracellular acidification occurs with a limited propionate uptake and volume increase (corresponding to the buffering capacity of the cytoplasm). If both protons and alkali cations are rendered permeable, a rapid salt influx and volume increase is observed. The latter can be quantitatively followed by electronic sizing methods. A detailed characterization of the system is provided through studies with ionophores, inhibitors of the red cell anion exchange system and drugs which activate or inhibit the Ca2+-induced K+ transport. It is demonstrated that in K-propionate media the permeability of the Ca2+-induced K+ pathway can be directly estimated. The method is suitable to observe population (all-or-none) responses in the activation of the K+ pathway under certain experimental conditions. The application of the method in the search for cation-proton exchanger systems is discussed and its use for demonstration purposes by producing selective lysis of red cells is described.