thromboplastin and 1-2-dilauroylphosphatidylcholine

This is a study of the morphology and transbilayer lipid distribution of human erythrocytes treated with chlorpromazine (CPZ) over extended time courses. At 0 degree C, treatment of dilauroylphosphatidyl[1-14C]choline-labeled erythrocytes with 120 microM CPZ produced an immediate stomatocytic transformation (t1/2 < 5 min) with no concurrent change in transbilayer distribution of radiolabeled lipid, as determined by bovine serum albumin extractability. At 37 degrees C, CPZ treatment of cells produced two sequential morphological effects: immediate stomatocytosis (t1/2 < 1 min) with no concurrent change in radiolabel transbilayer distribution, followed by gradual increase in stomatocytic extent over several hours, with concurrent redistribution of radiolabeled lipid to the inner monolayer. Cells pretreated with vanadate at 37 degrees C exhibited a triphasic morphological response: CPZ produced immediate stomatocytosis, followed by a transient reversion to echinocytes lasting about 2 h, before returning to stomatocytic morphologies over the next several hours. The echinocytic reversion was accompanied by exposure of phosphatidylserine on the cell surface, as indicated by increased activation of exogenous prothrombinase. These findings suggest that while CPZ induces transbilayer lipid redistribution over extended time periods (which may mediate the complex morphological transformations observed), the early stomatocytic response elicited by addition of CPZ is not due to lipid reorganization.

Topics: Antipsychotic Agents; Cell Size; Chlorpromazine; Erythrocytes; Humans; Membrane Lipids; Phosphatidylcholines; Phosphatidylserines; Serum Albumin, Bovine; Thromboplastin; Vanadates

Incubation of human platelets with unilamellar vesicles composed of dilauroylphosphatidylcholine (DLPC) induces shedding of small vesicular structures from the platelet plasma membrane. No significant cell lysis is observed during the process of shedding. Isolated spicules contain the major membrane glycoproteins, Ib, IIb, and IIIa, which are used to define the sidedness of the spicule membrane. These glycoproteins are completely susceptible to chymotrypsin treatment, whereas cytoskeletal proteins are inaccessible towards this enzyme. This demonstrates that the spicule membranes have a right-side-out orientation in as far as membrane proteins are concerned. Isolated spicules were 30-fold more active than platelets in stimulating prothrombin conversion to thrombin by the prothrombinase complex (factors Xa, Va and Ca2+). The increased prothrombinase activity reflects an increased amount of phosphatidylserine in the outer leaflet of the spicule membrane. Protein analysis of platelet spicules and native platelets reveals a number of differences, the most conspicuous of which is the virtual absence of myosin in the spicule preparations. It is proposed that a lack of myosin produces a different cytoskeletal organization in the spicules. This enables phosphatidylserine to become exposed at the outer surface of the spicule membrane.

Topics: Blood Platelets; Cell Membrane; Concanavalin A; Electrophoresis, Polyacrylamide Gel; Glycoproteins; Humans; Liposomes; Membrane Lipids; Membrane Proteins; Microscopy, Electron; Myosins; Phosphatidylcholines; Phosphatidylserines; Phospholipids; Thromboplastin; Wheat Germ Agglutinins