DIFFERENTIATION OF NA-K+ PUMPS OF LOW-K+ SHEEP RED-BLOOD-CELLS IS PROMOTED BY L(P) MEMBRANE-ANTIGENS()

Na+-K+ pumps of red blood cells from sheep of the low-K+ (LK) phenotyp e undergo differentiation during circulation, manifested in part by a striking increase in sensitivity to inhibition by intracellular K+ (K( i)). Pumps of red blood cells from sheep from the allelic phenotype, h igh K+ (HK), do not undergo this type of maturation. The hypothesis wa s tested that the L(p) antigen, found on LK but not HK cells, is respo nsible for the maturation of LK pumps. L(p) antigens have been shown t o inhibit LK pumps because anti-L(p) antibody stimulates the pumps by relieving inhibition by the antigen. L(p) antigens were recently shown to be molecular entities separate from Na+-K+ pumps [Xu, Z.-C., P. Du nham, J. Munzer, J. Silvius, and R. Blostein. Am. J. Physiol. 263 (Cel l Physiol. 32): C1007-C1014, 1992]. The test of the hypothesis was to modify the L(p) antigens of immature LK red blood cells with two kinds of treatments, anti-L(p) antibody and trypsinization (which cleaves L (p)), and to observe the effects of these treatments on maturation of pumps during culture of the cells in vitro. Both of these treatments p revented the maturation of the kinetics of the pumps to the K(i)-sensi tive pattern, supporting the hypothesis that interaction of the pumps with L(p) antigens is responsible for the maturation of the pumps. Str ong supportive evidence came from experiments on Na+-K+ pumps from rat kidney delivered into immature LK sheep red blood cells by microsome fusion. These rat kidney pumps, like endogenous red cell pumps, underw ent a maturational change whereby a K(i)-sensitive kinetic pattern dev eloped during in vitro culture, and this differentiation of the exogen ous kidney pumps was prevented by pretreatment of the microsome-fused cells with anti-L(p) antibody.