Some observations on pinocytosis in leucocytes

167

Morphological and metabolic observations have been made on the effects of endotoxin, deoxycholate, and digitonin (at less than 50/zg/ml) on polymorphonuclear leukocytes and mononuclear cells. The agents stimulate the respiration and glucose oxidation of these cells in a manner similar to that seen during phagocytosis. Electron microscopy revealed no morphological changes with the first two agents, but dramatic membrane changes were seen in the case of digitonin. Here tubular projections of characteristic size and shape formed on and split off the membrane. All the agents stimulated uptake of inulin, but efforts to demonstrate increased pinocytosis by electron microscopy have not so far succeeded, probably due to limitations in present experimental techniques.Studies of the biochemical changes that accompany phagocytosis have shown that the ingestion of solid particles by polymorphonuclear leukocytes (PMN) and mononuclear cells (MC) is accompanied by a stimulation of metabolism (1-4). Through the use of conventional metabolic inhibitors, it has been possible to establish which increases in metabolism are essential to the phagocytic process, and which appear to be only concomitants (1, 3, 4). In the case of PMN and MC, it has been shown that, although respiration may more than double during phagocytosis, this is merely incidental to the process of ingestion, and not essential. The approximately sevenfold increase in the oxidation of glucose-carbon-1 to CO2 is also an accompaniment to, rather than an essential part of, the process in PMN (1). Glycolysis is actually the energy-providing pathway for phagocytosis by both PMN and MC (1,4). In these two types of cell, another important stimulation of metabolism has been noted during uptake of particles, i.e., increased incorporation of a2Pi into complex phosphatides (4-6).It might be assumed that these changes in metabolism are associated with the involvement of the cellular membrane in phagocytosis, but it is clearly rather difficult to obtain rigorous evidence concerning the interrelationship between activities of the membrane and metabolic perturbations. The possibility of stimulating phagocytic cells without using solid phagocytizable objects has been considered as a potential aid to a better definition of the situation.On another level, there is a question as to whether the process of pinocytosis requires the expenditure of metabolic energy by the cell in the same way that phagocytosis does (7). This phe-

Section: Uptake Of Inulin By Stimulated Cellssupporting

confidence: 60%

Metabolic and Morphological Observations on the Effect of Surface-Active Agents on Leukocytes

Graham

Karnovsky

Shafer

et al. 1967

167

“…The failure to ingest colloids may represent, then, not a loss of the capacity for pinocytosis, but the development of discrimination by the cell membrane concerning what substances stimulate pinocytosis. Bennett (1956) has suggested that such a mechanism operates through specific affinities between the cell membrane and materials in the environment, and Tompkins (1953), Chapman-Andresen andPrescott (1956), andChapman-Andresen (1957) have demonstrated that environmental protein may evoke pinocytosis in amebae and mammalian cells. In suckling animals, fat is ingested in the upper small intestine and protein in the lower small intestine.…”

Section: Discussionmentioning

confidence: 99%

The Ingestion of Proteins and Colloidal Materials by Columnar Absorptive Cells of the Small Intestine in Suckling Rats and Mice

Clark

1959

408

141

Proteins and colloidal materials, administered orally to suckling rats and mice, were ingested by columnar absorptive cells of the jejunum and ileum, but not of the duodenum. Bovine gamma globulin and ovalbumin were identified in the apical cytoplasm by staining with fluorescent antibody; trypan blue, Evans blue, saccharated iron oxide, and colloidal gold were detected intraceliularly by their color, specific staining, and appearance in the electron microscope. Each substance was segregated in membrane-enclosed vacuoles, apparently part of a system of potentially interconnecting vacuoles and tubules in the apical cytoplasm which is continuous in places with the apical cell membrane. We postulate that ingestion of foreign materials was accomplished by pinocytosis, that is, by invagination of the apical cell membrane to form vacuoles containing materiaJ from the intestinal lumen.

“…As part of a study to elucidate cellular mechanisms controlling cell surface structure and function, we have selected uninucleate, freshwater, phagocytic amoebae as a model system . The functional simplicity of the amoeba cell surface is evidenced by the apparent lack of catalyzed transmembrane transport processes (10,11) and the presence of one or, at most, very few antigens (12) .…”

Section: Introductionmentioning

confidence: 99%

CHEMICAL CHARACTERIZATION OF THE ISOLATED CELL SURFACE OF AMOEBA

Allen

Ault

Winzler

et al. 1974

The cell surface has been isolated from uninucleate, freshwater, phagocytic amoebae by a new procedure . Several criteria were employed to demonstrate purity of the cell surface fraction . All morphological components of the tripartite surface were present in the isolated surface and the weight of the isolated surface was quantitatively accounted for by the components analyzed . Chemical analyses showed the presence of lipid, protein, and carbohydrate . Mannose was the predominant neutral sugar . Analyses for three different strains of Amoeba were similar . Phosphate was found to be the major anionic group in the cell surface material . Sulfate, uronic acid, sialic acid, muramic acid, and nonamidated glutamic acid and aspartic acid were absent . Evidence is presented suggesting that the phosphate is associated with an unidentified nonreducing polyol .