Amino acid transport in lymph node cells.

Recent, studies of antibody synthesis and secretion by lymph node cells (1,2) and of hormonal regulation of protein metabolism in striated muscle (3, 4) directed our attention to the functional significance of amino acid transport in protein synthesis (5). As an initial step in defining this relationship, the mechanism of amino acid transport in lymph node cells has been examined. Amino acid entry in these cells is mediated by two mechanisms: (a) a process characterized by saturation kinetics, high temperature coefficient, and functional irreversibility and (b) a first order process with the characteristics of passive diffusion. Amino acid exit,, at physiological concentrations, is primarily by diffusion, although carrier-mediated efflux is demonstrable at very low intracellular amino acid levels. The intracellularextracellular concentration gradient represents a steady state (e.g. equal rates of entry and exit), which can be altered by independent or concomitant changes in rates of either entry or exit. A kinetic analysis of amino acid transport, formulated on the basis of a carrier model, is presented that indicates that the lymph node cell membrane is asymmetric on its outer and inner surface with respect to the kinetic properties of the amino acid carrier. These data are discussed in the light of current concepts of amino acid transport.