Membrane transport by guinea pig peritoneal exudate leukocytes: Effect of phagocytosis on hexose and amino acid transport

Abstract

Short term, carrier mediated transport of D-glucose, L-leucine and L-lysine by guinea pig peritoneal macrophages was characterized. Analysis of the amino acid transport demonstrated two-limbed double reciprocal plots suggesting two transport systems for each amino acid. The low concentration limb of the curves established a K_m of 0.1 mM for L-leucine and 0.05 mM for L-lysine; V_max values were 2.0 and 2.85 nmole/mg protein/90 seconds, respectively. Leucine and lysine were shown to be competitive inhibitors of each other. Further competition studies revealed that other amino acids also had affinity for these carriers. Amino acid transport was found to be sensitive to sulfhydryl active compounds. Colchicine treatment of peritoneal macrophages did not inhibit the transport of the amino acids tested. Preloading macrophages with latex beads or heat-killed staphylocci by phagocytosis stimulated 2-deoxy-D-glucose (2-dOG) uptake markedly, but had no measurable effect on amino acid transport. Although total transport of 2-dOG increased in post-phagocytic macrophages, the kinetics of the system were not altered significantly. The K_m for both pre- and post-phagocytic transport of 2-dOG was shown to be 1.2 mM and the V_max was shown to increase from a pre-phagocytic value of 20 nmoles/mg protein/90 seconds to a post-phagocytic 27 nmoles/mg protein/90 seconds. Phagocytosis of heat-killed staphylococci by guinea pig polymorphonuclear leukocytes (PMNs), however, did not cause an augmentation in hexose transport in the cells. The presence of colchicine during phagocytosis did not alter subsequent uptake of amino acids by the macrophages.