Acta Biochimica et Biophysica 12. (1977)

1977 / 3. szám - Schubert, A.-Sarkadi, B.: Kinetic Studies on the Calcium-Dependent Potassium Transport in Human Red Blood Cells

Acta Biochim. et Biophys. Acad. Sei. Hung. Vol. 12 (3), pp. 207—216 (1977) Kinetic Studies on the Calcium-Dependent Potassium Transport in Human Red Blood Cells A. Schubert, B. Sarkadi Department of Physics, University of Agricultural Sciences, Gödöllő, and Department of Cell Metabolism, National Institute of Haematology and Blood Transfusion, Budapest Hungary (Received September 20, 1976) The kinetics of the Ca-dependent К transport across the human red cell mem­brane were studied under experimental conditions allowing the separation of this step from the previous membrane events. Net potassium and tracer potassium fluxes were measured and a self-consistent model was constructed for calculating the ionic perme­ability values. All the experimental results could be interpreted by means of a non­saturable neutral К selective channel. In net К efflux measurements the accompanying Cl movement was found to be rate-limiting, and the charge-carrying Cl permeability of the red cell membrane could be calculated. Introduction The membrane red cells incubated in vitro is known to become selectively permeable to К ions under various experimental conditions (e. g. high concentra­tions of NaF, iodoacetate + metabolic depletion, iodoacetate + inosine, triosere­­ductone, propranolol or the Ca-ionophore A-23187, see for ref. Orringer, Parker, 1973; Riordan, Passow, 1973; Gárdos et al., 1975). In any of these cases the Na­­permeability of the membrane remains unaffected and the phenomenon is highly Ca-dependent. The overall kinetics of this Ca-dependent К transport consist of at least four steps: 1. entry of Ca into the cells; 2. binding of Ca ions to specific membrane receptors; 3. formation of the К-transporting configuration of the membrane; 4. translocation of К ions (Lew, 1974; Szász, Gárdos, 1974). In the present work an attempt was made to study the fourth step separately and to construct a self-consistent model for all the observed characteristics of the К transport step. Preliminary considerations A) In order to separate the K. transport step from the preceeding ones, kinetic measurements were carried out by using propranolol-treated red cells, in which ions were transported across the membrane at a maximum rate and efficacy (Szász et al., 1974; Gárdos et al. 1975). B) To maintain electroneutrality, a net К transport has to be accompanied by a cotransport of anions and/or a countertransport of cations. The orders of Acta Biochimica et Biophysica Academiae Scientiarum Hungaricae 12, 1977

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