The Na:K pump in red cells is electrogenic

The membrane potential, E, of the red cell measured with a fluorescent dye, 3,3'-dipropylthiadicarbocyanine iodide, hyperpolarizes when the Na:K pump is activated by adding external K and depolarizes upon the subsequent addition of ouabain. The electrogenic pump is optimally observed in cells where internal Na+ has been raised, SO2-(4) has replaced Cl-, and SO2-(4) permeability has been inhibited by 4,4'-diisothiocyanostilbene-2,2'-disulfonate (DIDS)). The change in E associated with the electrogenic component is about 6 mV in human red cells, somewhat smaller in sheep, and larger in duck and Amphiuma red cells. The membrane resistance, Rm, can be estimated from the pump-dependent change in E and from the current flow assumed to be one-third the ouabain-sensitive Na efflux. In human red cells, Rm is about 1 X 10(6) ohm-cm2. Rm calculated from the residual DIDS-insensitive SO2-(4) flux is also about 1 X 10(6) ohm-cm2. The closeness of these two values of Rm is paralleled in the other three types of red cells (even though the absolute values of Rm vary among the four types by a factor of 10), indicating that the net current flow across the membrane can be accounted for by the net transport of Na by the pump.