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

Abstract

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-

Respiration and glucose oxidation in human and guinea pig leukocytes: comparative studies

“…Further, when inert particles (latex spherules) were used instead of bacteria in phagocytosis experiments similar to those of Zatti and Rossi, no increase in granule NADPH oxidase specific activity was noted, even though ingestion of these spherules produces a normal respiratory burst. It is possible that in the experiments of Zatti and Rossi with the phagocytizing cells, some effects not related to phagocytosis per se were introduced, i.e., effects due to still operative enzymes of the dead bacteria they used or nonspecific effects such as those due to surfactants, endotoxins, or other components of the organisms (28)(29)(30). These could have produced a situation similar to that described above for saponin.…”

Effects of Phorbol Myristate Acetate on the Metabolism and Ultrastructure of Neutrophils in Chronic Granulomatous Disease

“…Surface-active agents, such as digitonin, deoxycholate, and saponin, cause increased oxygen consumption and glucose oxidation by PMN, while others, including Triton X-100, Tween-80, cetylpyridinium chloride, lauryl sulfate, and vitamin A alcohol, have little or no effect on metabolism (38). Electron microscope studies have revealed marked changes in the surface membranes of PMN treated with digitonin, but none of the surface active agents stimulating neutrophil metabolism has been reported to initiate cytoplasmic vacuole formation.…”

H2O2 release from human granulocytes during phagocytosis. I. Documentation, quantitation, and some regulating factors.

“…In support of the concept that perturbations in the plasma membrane are responsible for triggering H20O formation, it has been shown that membrane-active agents such as endotoxin, deoxycholate, digitonin, and chemotactic factors (24,25) all produce a stimulation of the leukocyte pentose shunt without inducing phagocytosis. Stimulated pentose shunt activity indirectly indicates increased intracellular H202 levels (1,21).…”