Active and passive Ca movements in dog red blood cells and resealed ghosts

Dog red blood cells accumulate Ca rapidly when deprived of substrate or cooled to 5 degrees C. The latter effect is reversible as the cells are rewarmed to body temperature. Resealed ghosts extrude Ca, provided ATP is incorporated in them. Passive fluxes of Ca are stimulated by Na on the opposite side of the membrane, consistent with a model for Ca-Na countertransport. Quinidine, cell shrinkage, and low pH--all known to suppress net Ca influx--have no accelerating effect on Ca efflux, thus validating earlier conclusions about the variability of the coupling ratio for Ca-Na exchange. The significance of these findings for cell volume regulation is discussed.