The mechanisms of three membrane transport pathways for Na and K will be studied, along with some aspects of their regulation. The Na/K pump and the K/C1 and Na/K/C1 cotransporters are the transport pathways. In LK sheep red cells, specific membrane antigens modulate the Na/K pump and the K/C1 cotransport. Using the antigens and antibodies as probes of transport can help elucidate aspects of the mechanisms of transport. K/C1 cotransport in the sheep cells and in resealed human red cell ghosts is sensitive to osmotically induced changes in cell volume. A "regulator" protein, with critical sulfur groups, may be responsible for volume-transport coupling. Ghosts passed through a gel filtration column lose the transport pathway and also membrane proteins. This experimental system may permit identification of the "regulator" protein, and lead to its use to reconstitute transport in the ghosts. Metabolic aspects of volume-transport coupling, involving protein kinase C, will be studied in intact cells, resealed ghosts, and inside-out vesicles of red cell membranes. A related pathway, Na/K/C1 cotransport, will be characterized in human red cells and Ehrlich ascites cells in terms of basic mechanism and metabolic control of volume-transport coupling. An understanding of the molecular mechanisms of transport, and their control by the interactions between membrane components, will require reconstitution of the isolated components in a functional state. The membrane complexes will be reconstituted in liposomes and in affinity columns. To be isolated and reconstituted in the appropriate combinations are: the two antigens from sheep red cells, the Na/K pump and K/C1 cotransporter from rabbit kidney, the "regulatory" protein from human red cells, and the Na/K/C1 cotransporter from ascites cells. The mechanisms to be studied relate directly to epithelial function and to control of cell volume in general. In addition the reconstituted membrane complexes will provide useful model systems for membrane receptor-enzyme complexes, involved in stimulus-response coupling of cellular functions.