The overall objective is to contribute to an understanding of the mechanism of active transport of Na and K. The approach will involve comparing high-K and low-K cells from sheep and goats with respect to a number of properties. These will include: the kinetic properties of active and passive fluxes of Na and K and the effect on the kinetics of an antibody, anti-L, which has been shown in preliminary experiments to stimulate K transport in LK sheep cells; the numbers of Na-K pump sites (determined by measuring H3-ouabain binding) and the control of these numbers during development and by anti-L treatment; the partial reactions of the Na, K-ATPase system and the effects on them of anti-L serum. Results of these experiments should provide information on the nature of and interaction between subcomponents of the Na-K pump. In addition it is hoped to test and extend a working hypothesis which was put forward in an attempt to explain the nature, determination, and control of the HK-LK system. This hypothesis includes, among other aspects, an interconvertibility between Na-K pump and leak sites which controlled genetically, takes place during development of LK cells, and is mediated in vitro by anti-L serum. Finally it is proposed to investigate relation between active transport of various solutes (K, amino acids, sugars) and endocytosins in leukocytes. This problem relates to the leukocytic functions in immune responses and inflammation.