PASSIVE POTASSIUM-TRANSPORT IN LK SHEEP RED-CELLS - EFFECTS OF ANTI-L ANTIBODY AND INTRACELLULAR POTASSIUM

The passive K influx in low K (LK) red blood cells of sheep saturates with increasing external K concentration, indicating that this mode of transport is mediated by membrane-associated sites. The passive K influx, .**GRAPHIC**. is inhibited by external Na. Isoimmune anti-L serum, known to stimulate active K transport in LK sheep red cells, inhibits .**GRAPHIC**. about 2-fold. .**GRAPHIC**. is affected by changes in intracellular K concentration. [K]i, in a complex fashion: increasing [K]i from near zero stimulates .**GRAPHIC**. while further increases in [K]i, above 3 mmol/l cells, inhibit .**GRAPHIC**. The passive K influx is not mediated by K-K exchange diffusion. The effects of anti-L antibody and [K]i on passive cation transport are specific for K: neither factor affects passive Na transport. The common characteristics of passive and active K influx suggest that .**GRAPHIC**. is mediated by inactive Na-K pump sites, and that the inability to translocate N characterizes the inactive pumps. Anti-L antibody stimulates the K pump in reticulocytes of LK sheep. Anti-L has no effect on .**GRAPHIC**. in these cells, apparently because reticulocytes do not have the inactive pump sites which, in mature LK cells, are a consequence of the process of maturation of circulating LK cells. Anti-L probably alters the maximum velocity of both active and passive K fluxes by converting pump sites from a form mediating passive K influx to an actively transporting form.