The outflux of Na24 from prelabeled ghosts was measured under various conditions. Prelabeling was accomplished by hypotonic hemolysis of intact human cells in the presence of tracer Na24. The resultant ghosts when subsequently washed were found to retain 10 to 20 per cent of the initial Na24. Separate experiments indicated that this trapped amount resides in only a portion of ghosts comprising the total population. The characteristics of the outflux of this residual Na24 indicated that the ghost system closely resembles intact red cells. The outflux of Na from ghosts could be divided into three components: active and passive transport and exchange diffusion. The active transport system, necessarily driven by metabolism, required the presence of K in the extracellular phase and was blocked by strophanthidin. The concentration dependence of the Na pump flux on the external K and internal Na appeared the same in ghosts as in intact cells. Certain other features of this ghost system are also discussed.

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