Phin Cohen

Initiation of phospholipase A2 activity in human platelets by the calcium ion ionophore A23187.

Phospholipase A2 activity in a suspension of intact platelets was induced by addition of a Ca2+-ionophore, A23187. This action of ionophore A23187 was enhanced by EGTA and inhibited by an excess of Ca2+ in the medium, findings which suggest that A23187 is able to mobilize intracellular Ca2+ for the latters role as an essential cofactor for phospholipase A2 activity.

Comparison of Phospholipid and Fatty Acid Composition of Human Erythrocytes and Platelets

Summary. The phospholipid and fatty acid composition of the diacyl and plasma‐logen derivatives of the choline and ethanolamine phosphoglycerides of human erythrocytes and platelets have been compared.

Quantification of human platelet inositides and the influence of ionic environment on their incorporation of orthophosphate-32P

Platelets are a rich source for the study of inositol lipids in man. The substitution of an EDTA-KCl solution for the water component of the Bligh and Dyer procedure permitted quantitative extraction of polyphosphoinositides. The latter, with monophosphoinositide, were found to comprise, on a molar basis, 6.7% of total platelet phospholipids. Study of the incorporation of orthophosphate-(32)P into platelet phospholipids was further simplified by separating eight (32)P-labeled lipids, including the inositides, with a single chromatographic development on formaldehyde-treated paper. Particular attention was paid to the influence of ionic environment on the pattern and degree of labeling. In 300 mOsm media major phospholipids other than the inositides were not labeled. Small amounts of label appeared in certain trace phospholipids, notably phosphatidic acid. In 150 mOsm media, labeling of inositides was moderately increased, that of trace phospholipids enormously so. The increased labeling was not solely due to thrombocytolysis since (a) platelet disruption by sonication or freeze-thawing abolished (32)P incorporation into phospholipids and (b) in timed studies, restoration of osmolarity to 300 mOsm by addition of hypertonic sorbitol blunted the enhancement effect of previous 150 mOsm exposure. Lowering K and compensatorily increasing Na concentration of 300 mOsm media also stimulated (32)P labeling of inositides and, to a lesser extent, the trace phospholipids. However, the pattern and degree of stimulation were not as strikingly altered as in the osmolarity studies. These data show that drastic alterations of ionic environment can sharply influence the platelets ability to incorporate orthophosphate-(32)P into its phospholipids.

Distribution of Fibrinogen, and Platelet Factors 4 and XIII in Subcellular Fractions of Human Platelets

The distribution of fibrinogen, platelet factor 4 (heparin‐neutralizing factor) and factor XIII amongst subcellular fractions of human platelets was determined. It was found that fibrinogen and platelet factor 4 peaked sharply in the region of the density gradient previously shown to be heavily enriched with α‐granules. By contrast, factor XIII, fibrin‐stabilizing factor, was found exclusively in the supernatant.

Pathways of fatty acid metabolism in human platelets

The metabolic fate of (14)C-labeled fatty acids which have been incubated with human platelets, has been traced. The following has been shown. (a) Intact platelets have a considerable capacity to oxidize fatty acids. (b) When tracer amounts of four of the most common fatty acids in normal plasma were incubated with platelets, each showed a distinctive pattern of uptake among neutral lipids and phospholipids. With regard to the latter, it was shown that these distribution patterns were, in most cases, similar to those of the fatty acids found in natural platelet phospholipids. (c) By increasing the time of incubation or the amount of added oleic acid, the distribution of oleic acid uptake between lecithin and other phosphoglycerides was altered so that a larger share was incorporated into the latter. (d) The effects of added lysolecithin or lysoethanolamine phosphoglycerides on oleic acid incorporation into platelet phosphoglycerides are quite variable. At low concentrations, added lysolecithin functions chiefly as a reaction partner for oleic acid. Added adenosine triphosphate and CoASH augment the incorporation of oleic acid into lecithin over a wide range of added lysolecithin (12.5-500 mumoles/liter). At higher concentrations of added lysolecithin, in the absence of ATP and CoASH, oleic acid incorporation into lecithin is considerably reduced. Also, added lysolecithin and lysoethanolamine phosphoglycerides, in the absence of ATP and CoASH, are able, at certain concentrations, to stimulate oleic acid incorporation into all except the serine phosphoglycerides. (e) Platelets appear to have a de novo pathway for renewal of lecithin.

Energy substrate metabolism in fresh and stored human platelets

The latent capacity of human platelets for oxidizing several important energy-yielding substrates has been revealed by hypoosmolaric incubation conditions. The data show that the human platelet has a considerable capacity to oxidize both glucose and long-chain fatty acids. Long-chain fatty acids appear to rank favorably with glucose as a potential energy substrate. In a number of mammalian tissues, (-)-carnitine serves to regulate the rate at which long-chain fatty acids are oxidized. Evidence was obtained which suggests that (-)-carnitine functions in a similar role in the platelet. After storage of human platelets at 4 degrees C for 24 hr, the oxidative capacity for glucose was reduced by approximately 25% and for long-chain fatty acids by almost 50%. Investigation of the component parts of the metabolic pathways indicated that a marked decrease in the capacity of the Krebs cycle could be responsible for the decrement in energy substrate oxidation.

Platelet Life Span

In the past decade platelet transfusions into thrombocytopenic recipients indicated that the platelet had a curvilinear lifespan. These early studies showed that platelet transfusions could be used to demonstrate shortened lifespans of platelets in idiopathic acute and chronic thrombocytopenic purpura. In addition, progressive shortening of the platelet lifespan followed the administration of multiple transfusions.

Relationship between membrane function and permeability. I. Similarity of 'platelet factor-3' availability in pure erythrocyte and pure platelet suspensions.

As the osmolarity of the medium decreases, ‘platelet factor‐3’ (PF‐3) availability increases in erythrocyte as well as platelet suspensions. Associated with this is a parallel increase in PF‐3 activity of the cell‐free supernatant.

Relationship between Membrane Function and Permeability: III. FURTHER EVIDENCE LINKING MEMBRANE TRANSPORT AND THROMBOPLASTIN AVAILABILITY OF THE INTACT ERYTHROCYTE

Summary Within a series of short straight‐chain compounds resembling glycerol in structure, the pattern of unmasking of erythrocyte ‘platelet factor 3’ (PF‐3) activity appeared to be related to a combination of cell penetrability, molecular weight and complement of hydroxyl groups. The same relationship held in a series of low molecular weight polymers of ethylene glycol. Moreover, propylene glycol and ethylene glycol monomethylether, at very low concentrations, were shown to delay glycerol‐induced erythrocyte PF‐3 enhancement. Among penetrating non‐electrolytes not having a structural similarity to glycerol, dimethylsulphoxide was the only compound that had a family of PF‐3 enhancement curves of the glycerol type.

Distortions of normal bone cell metabolism induced in multiple myeloma

Abstract Samples of bone marrow infiltrated with myeloma cells derived from iliac crest biopsies taken from 12 patients with multiple myeloma were studied in vitro in an attempt to discover the cause of the bone lesions characteristic of the disease. The relative affinities of the two cell types for glucose and proline were examined and found to be similar making inhibition of bone matrix biosynthesis due to competion for substrate unlikely as a cause for bone destruction. Measurements of incorporation of proline into bone cells and matrix revealed increased retention of label in cells (seemingly in a macromolecule) but generally normal incorporation into collagen. Parallel studies of myelomatous marrow suggested that these changes involved a change in bone cell metabolism per se and were not the result of marrow contamination. Collagenase activity was normal or low in the bone cells of four patients and virtually absent from marrow and plasmacytomas, thus ruling out abnormal biosynthesis of collagenase as a cause of bone destruction. These data are interpreted as indicating a redirection and stimulation of bone cell biosynthetic mechanisms as a result of the invasion of the marrow by Myeloma cells. The nature of the material (presumed to be protein) made is unknown.