The influx of calcium ions into human erythrocytes during cold storage. The influences of extracellular pH, intracellular adenosine triphosphate and efflux of univalent cations

Abstract

1. When human erythrocytes are stored at 3°C for several days as a suspension in isoosmotic sucrose or KCI, containing CaCl2, the rates of cellular ATP degradation are similar. 2. During cold storage oferythrocytes in sucrose-CaCl2 medium, Ca2+ influx and univalent-cation efflux occur, the pH value of the suspending medium rises and the intracellular pH falls. These pH changes correlate reasonably well with alterations in the membrane potential calculated from Cl-distribution. 3. The presence of Ca2+ in the medium does not increase the rate of univalent-cation efflux from the cells. 4. When the pH of the medium is raised by addition of buffers, the rates of both Ca2+ influx and univalent-cation efflux increase. 5. Replacement of sucrose by KCI as the main osmotic component of the medium completely suppresses Ca2+ influx and univalent-cation efflux, although the pH of the KCI medium is higher than that of the sucrose medium. 6. When sucrose is replaced by choline chloride, Ca2+ influx and univalent-cation efflux still occur, and the pH of the medium is similar to that found in iso-osmotic KCI. 7. When valinomycin, Pb2+ or Cd2+ are added to the iso-osmotic sucrose medium, the rate of efflux of univalent cations increases as also does the influx of Ca2+. 8. From these and other observations, it was concluded that it is univalent-cation efflux rather than ATP depletion or elevated extracellular pH which is the prerequisite for Ca2+ influx during cold storage.