Changes in membrane microviscosity associated with phagocytosis: effects of colchicine.

Abstract

The effects of phagocytosis on plasma membrane microviscosity were studied by fluorescence depolarization techniques. It was shown that lipophilic probes are accumulated in intracellular vesicles to a significant degree in fibroblasts and neutrophils. Microviscosity was thus determined from the behavior of probes in isolated membranes. Phagocytosis of oil emulsions or polystyrene beads by rabbit polymorphonuclear leukocytes induces a marked decrease in plasma membrane microviscosity that parallels the extent of phagocytosis. Liposomes made from extracts of membrane lipid show qualitatively the same changes, indicating that the alteration of microviscosity results at least in part from changes in lipid composition. The decrease in microviscosity is abolished when colchicine is present during phagocytosis. Addition of-colchicine to membranes previously isolated from control or phagocytic cells has no effect on their microviscosity. The results suggest that phagocytosis is accompanied by a microtubule-dependent reorganization of membrane lipids. During phagocytosis, particles are enveloped by plasma membrane and subsequently internalized. In polymorphonuclear'leukocytes (PMN), this process is accompanied by striking changes in the composition of the residual plasma membrane. For example, certain lectin receptors are selectively removed from the surface (1) while transport proteins are selectively spared (2). Treatment of cells with low doses of colchicine, an inhibitor of microtubule assembly, prevents the induced topographical changes without affecting the rate or amount of ingestion (1, 3). The existence of these colchicine-sensitive phenomena indicates a role for microtubules in the control of membrane topography. Further, the large and rapid membrane reorganization accompanying phagocytosis provides a unique system for analyzing the consequences of microtubule-membrane interaction at the molecular level.We report here studies of the microviscosity of the plasma membrane of phagocytic cells. Microviscosity was inferred from the fluorescence depolarization of lipophilic probes embedded in isolated plasma membranes and in liposomes made from extracts of the membranes. Large changes in microviscosity are observed which parallel the degree of phagocytosis. Colchicine has no direct effect on membrane microviscosity, but blocks changes induced by phagocytosis. METHODSThe fluorescence polarization method used for the study of membrane microviscosity has been described extensively (4) and has been used with artificial liposomes (4, 5,), membranes (6), and whole cells (7,8). The polarization of-fluorescence is determined by the rotation of the probe during the lifetime of the excited state. The rotation of the probe in turn is dependent on the viscosity of its environment ("microviscosity")-rapid Abbreviations: DPIH, 1,6-diphenyl-1,3,5-hexatriene; PMN, polymorphonuclear leukocytes; BSA, bovine serum albumin. rotation leading to depolarization. By determining the polarization of the probe in media of known viscosi...

Fusion of isolated myoblast plasma membranes. An approach to the mechanism

“…This was interpreted by the production of membrane domains of lower and higher rigidity induced by Ca 2 +. A similar lateral phase separation has been observed to be associated with phagocytosis [40]. Apparently, these different domains are stable in the presence of Ca 2 + at temperatures between 2 and 37° C, and the thermallyinduced mixing of these different phases might therefore occur only at temperatures above 37°C.…”

Hypothyroidism Modifies Lipid Composition of Polymorphonuclear Leukocytes

“…Regarding circulating lipid levels, our results (Table 2) are consistent with others' previous findings which also showed changes in serum lipid composition hallmarked by increased TC and LDL-C contents in HT individuals [3,34,37]. However, the HDL-C was not altered in our experimental model.…”

“…Maintenance of the physiological lipid composition in the phagocyte cells is essential for proper biomembrane structure and function, and for the normal functional performance of this type of immune cells [33,34]. Here, we studied the effects of hypothyroidism on lipid levels and on lipid metabolizing enzymes expression in the PMN cells.…”

Hypoparathyroidism, Retardation, and Dysmorphism Syndrome: Impaired Early Growth and Increased Susceptibility to Severe Infections Due to Hyposplenism and Impaired Polymorphonuclear Cell Functions

“…These functions are highly dependent on the ability of these cells to internalize particles and on other events that are coupled to or triggered by phagocytosis (e.g., secretion, oxidative burst). MTs influence cell surface function in polymorphonuclear cell (PMN) (5). We hypothesized that PMN of HRD patients could have impaired functions due to the MT assembly defect in these patients.…”