Anion-coupled Na Effiux Mediated by the (original) (raw)

2013

Abstract

The red cell Na/K pump is known to continue to extrude Na when both Na and K are removed from the external medium. Because this ouabainsensitive flux occurs in the absence of an exchangeable cation, it is referred to as uncoupled Na efflux. This flux is also known to be inhibited by 5 mM Na o but to a lesser extent than that inhibitable by ouabain. Uncoupled Na efflux via the Na/K pump therefore can be divided into a Nao-sensitive and Nao-insensitive component. We used DIDS-treated, SO4-equilibrated human red blood cells suspended in HEPES-buffered (pH o 7.4) MgSO 4 or (Tris)~SO4, in which we measured ~2Na efflux, SSso4 efflux, and changes in the membrane potential with the fluorescent dye, diS-C s (5). A principal finding is that uncoupled Na efflux occurs electroneutrally, in contrast to the pump's normal electrogenic operation when exchanging Na i for K o. This electroneutral uncoupled efflux of Na was found to be balanced by an effiux of cellular anions. (We were unable to ...

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