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Biomedical subjects

J M Gerrard

Publications and source records attributed to J M Gerrard.

At least 109 records · Page 6Linked to original sources
PubMed1983

Halothane stimulates the aggregation of platelets of both normal individuals and those susceptible to malignant hyperthermia.

Platelet responses to halothane in normal individuals and in patients susceptible to malignant hyperthermia were evaluated. Platelets in platelet-rich plasma from both normal controls and patients underwent aggregation in response to halothane. There was no significant difference in the degree of aggregation between normal subjects and patients. Aggregation by halothane was associated with a change in platelet shape, centralization of platelet granules, and phosphorylation of platelet actin binding protein, myosin light chain, and a 40 000-dalton protein. Aggregation induced by halothane could be inhibited by EGTA, PGE1, adenosine and verapamil, but not by aspirin. Aggregation induced by halothane could be potentiated by small doses of adrenaline or ADP and in some individuals by caffeine. However, previous exposure of platelets to halothane made them subsequently less aggregable to ADP. The results of these studies do not support a use of halothane-induced aggregation of platelets to detect an abnormality in individuals susceptible to malignant hyperthermia, but do provide new evidence of the effects of halothane on cellular function.

Adenosine Diphosphate↗
PubMed1982

Biphasic modulation of platelet phospholipase A2 activity and platelet aggregation by mepacrine (quinacrine).

The modulation of rat platelet phospholipase A2 (phosphatide 2-acylhydrolase, EC 3.1.1.4) and rat platelet aggregation by mepacrine was investigated. The 2-acyl specificity of phospholipase A2 activity was confirmed by using 1-[14C]palmitoyl-2-[3H]arachidonylphosphatidylcholine as substrate. Under optimal pH, phospholipase A2 activity was not affected by aspirin but was inhibited by indomethacin. Contrary to previous reports, a biphasic modulatory role of mepacrine on phospholipase A2 activity and platelet aggregation was demonstrated. The data suggest that platelet aggregation is mediated via phospholipase A2.

Animals↗
PubMed1982

Separable assembly of platelet pseudopodal and contractile cytoskeletons.

Unactivated platelets contain about 69% G actin and less than 10% of the contractile proteins in a cytoskeletal core resistant to extraction with 1% Triton X-100. Activation by thrombin leads, within 1 min, to the formation of pseudopodia and contractile gels, accompanied by the reduction of the G-actin content to about 22% and the development of cytoskeletal cores containing 70%-80% of the total actin and 60%-80% of the total myosin and actin-binding protein. Inhibition of pseudopodal formation by pretreatment with cytochalasin B before thrombin activation results in the loss of most of the actin-binding protein and about one third of the actin from the cytoskeletal core. Myosin incorporation and contractile gel formation are unaltered by this treatment. Conversely, activation with phorbol 12-myristate 13-acetate leads to pseudopodal but not contractile gel formation, with cytoskeletal cores containing mostly actin and actin-binding protein. These results demonstrate that there are separable cytoskeletal assembly processes in platelets for pseudopodal and contractile gel formation.

Actins↗
PubMed1982

Identification of prostaglandins and other arachidonic acid metabolites in experimental otitis media.

Although prostaglandins (PGs) have been detected in the middle ear fluids, the exact identification of PGs, and other arachidonic acid (AA) metabolites has not been made. The AA metabolites were identified in experimentally induced serous otitis media and purulent otitis media in chinchillas using a radiochromatography method. The relative abundance of each metabolite synthesized was also determined. The major AA metabolites, 6-Keto-PGF1 alpha and 15-hydroxy-5,8, 11, 13-eicosatetraenoic acid (15-HETE), were positively identified by gas chromatography-mass spectrometry. The AA metabolites in Eustachian tube obstructed middle ear mucosa (MEM) were predominantly 6-Keto-PGF1 alpha, followed by PGD2, 115-HETE, hydroxyheptadecatrienoic acid (HHT), PGF2 alpha and PGE2. In infected MEM, the predominant product was 15-HETE followed by 6-Keto-PGF1 alpha, PGD2, HHT, PGF2 alpha, and PGE2. The possible role of PGs and other AA metabolites in the pathogenesis of otitis media will be discussed.

Animals↗
PubMed1982

Ultrastructure of clots during isometric contraction.

We explored the retraction or contraction of platelet-fibrin clots under isometric conditions. In the presence of micromolar calcium clots of normal platelet-rich plasma developed tension at an initial rate of 0.1 to 0.2 g/min per cm2 (initial cross-sectional area). Electron microscopy of clots fixed after attaining a force of 1.6 g/cm2 revealed platelets with elongated bodies and pseudopods in close apposition to fibrin strands which were oriented in cablelike fashion in the direction of tension. The development of tension could not be explained simply on the basis of platelet-platelet association and interaction alone. First, factor XIII-dependent cross-linking of fibrin fibers was critical to normal isometric contraction. Second, tension decreased linearly, rather than exponentially, when the platelet count in the platelet-fibrin clot was decreased, suggesting that platelets must be interacting with another component (i.e. fibrin). Thrombasthenic platelets, deficient in fibrinogen receptors, failed to develop tension or to align fibrin strands or pseudopods in the clot. Platelet-fibrin clots treated with vincristine to disassemble microtubules or cytochalasin B to disrupt microfilaments failed to develop tension and relaxed if these agents were added after tension had developed. Relaxation under these conditions, however, was not associated with loss of orientation of fibrin strands. Our findings suggest that platelet-fibrin interaction in clots under isometric conditions leads to orientation of fibrin strands and platelets in the direction of force generation. Tension develops as platelets simultaneously attach to and spread along fibrin strands, and contract. The contraction draws some fibrin into platelet-fibrin clumps and aligns other strands in the long axis of tension. The achievement and maintenance of maximum tension appears to depend on the development of platelet-fibrin attachments and extension of platelet bodies and long pseudopods containing bundles of microfilaments and microtubules along the oriented fibrin fibers.

Blood Platelets↗
PubMed1982

Plasminogen, plasminogen activator, and platelets in the regulation of clot lysis. Reconstitution and patient studies.

Dilute clot lysis was assayed by release of soluble 125I fibrin degradation products from dPPP clots containing varying amounts of plasminogen activator and platelets. Plasminogen activator in the absence of platelets gave an approximately linear rate of lysis, with a rate proportional to its concentration. Addition of platelets to achieve normal clot retraction had little effect on the lysis rate in the absence of plasminogen activator or in the presence of very high plasminogen activator levels. However, with intermediate plasminogen activator levels, platelet-mediated clot retraction was associated with an accelerated rate of clot lysis when retraction reached 75% to 90%. The length of the lag phase before the start of the accelerated phase varied with the number of platelets and rate of clot retraction. The interaction of clot retraction and lysis was further explored in selected patients to determine (1) whether the contributions of platelet and plasma factors in these cases was similar to those seen in our studies of reconstituted plasma and (2) whether our experience with reconstituted systems could be used in the study of disorders of fibrinolysis involving platelets and fibrinolytic enzymes.

Blood Coagulation↗
PubMed1982

Phosphorylation of platelet actin-binding protein during platelet activation.

In this study we have followed the 32P-labeling of actin-binding protein as a function of platelet activation. Utilizing polyacrylamide-sodium dodecyl sulfate gel electrophoresis to resolve total platelet protein samples, we found 2--3-fold labeling increases in actin-binding protein 30--60 sec after thrombin stimulation. Somewhat larger increases were observed for 40,000 and 20,000 apparent molecular weight peptides. The actin-binding protein was identified on the gels by coelectrophoresis with purified actin-binding protein, its presence in cytoskeletal cores prepared by detergent extraction of activated 32P-labeled platelets, and by direct immunoprecipitation with antibodies against guinea pig vas deferens filamin (actin-binding protein). In addition, these cytoskeletal cores indicated that the 32P-labeled actin-binding protein was closely associated with the activated platelet's cytoskeleton. Following the 32P-labeling of actin-binding protein over an 8-min time course revealed that in aggregating platelet samples rapid dephosphorylation to almost initial levels occurred between 3 and 5 min. A similar curve was obtained for the 20,000 apparent molecular weight peptide. However, rapid dephosphorylation was not observed if platelet aggregation was prevented by chelating external calcium or by using thrombasthenic platelets lacking the aggregation response. Thus, cell-cell contact would seem to be crucial in initiating the rapid dephosphorylation response.

Animals↗
PubMed1981

Fibrinogen is the receptor for the endogenous lectin of human platelets.

Washed platelets activated by alpha-thrombin, gamma-thrombin, thrombocytin or the ionophore A23187 (ref. 3) lose their disk shape, produce pseudopodia and become cohesive. This cohesiveness is accompanied by the expression of an endogeneous haemagglutinin which, although apparently bound to the platelet membrane, is dependent on cell secretion. The interaction of this agglutinin with appropriate receptors on other platelets is believed to be responsible for aggregation. We report here that platelets can be prepared which lack agglutinin activity but have receptor function, that afibrinogenaemic platelets lack receptor activity, and that fibrinogen is the receptor for the agglutinin secreted by activated platelets.

Blood Platelets↗
PubMed1981

Stimulation of platelet protein phosphorylation by arachidonic acid and endoperoxide analogs.

The present study has investigated the influence of arachidonate, endoperoxide analogs, and the calcium ionophore A23187 on platelet aggregation and on the phosphorylation of platelet proteins. Following stimulation of platelets by these agents a rapid increase in phosphorylation of three proteins was observed which began at the same time as the initial formation of platelet aggregates. These three proteins were the 260,000 dalton actin-binding protein, a 40,000 dalton protein in unknown function, and the 20,000 dalton myosin light chain. When extensive aggregation was reached, the extent of phosphorylation returned toward baseline. Pretreatment of platelets with aspirin completely inhibited both aggregation and protein phosphorylations induced by arachidonate, but had only partial inhibitory effects on endoperoxide analogs or A23187. Since endoperoxide analogs and A23187 may trigger endogenous production of prostaglandin endoperoxides and thromboxane A2, in addition to having a direct effect of their own, it is probable that the partial inhibition seen was due to inhibition of that component of their effect due to this endogenous production, though other effects of aspirin can not be entirely ruled out. Since recent evidence shows that phosphorylation of myosin light chain results from calcium stimulation of a protein kinase in the presence of calmodulin, the results are consistent with mobilization of calcium as the primary role of the arachidonate-endoperoxide-thromboxane pathway.

Arachidonic Acid↗
PubMed1981

Platelet aggregation independent of ADP release or prostaglandin synthesis in patients with hermansky-Pudlak syndrome.

Platelets from patients with the Hermansky-Pudlak (HPS) syndrome are deficient in the storage pool of adenine nucleotides and serotonin. As a result, the storage pool deficient (SPD) platelets develop only single waves of clumping when stimulated by threshold concentrations of aggregating agents which cause irreversible, biphasic aggregation of normal platelets. Yet, patients with HPS either have no bleeding problems or only mild symptoms. In the present study we have evaluated the importance of prostaglandin synthesis and secretion to the irreversible aggregation of HPS platelets. Results of the study demonstrate that aspirin-treated SPD platelets, which cannot form thromboxane or undergo the release reaction on stimulation by arachidonate, can still undergo irreversible aggregation in response to thrombin and ADP if treated first with epinephrine. A mechanism of membrane modulation mediated by alpha-adrenergic receptors cooperatively linked to the endoperoxide and thromboxane receptor can secure irreversible aggregation of normal or abnormal platelets despite absence of secretion and prostaglandin synthesis.

Adenosine Diphosphate↗
PubMed1981

Salicylic acid inhibition of the irreversible effect of acetylsalicyclic aicd on prostaglandin synthetase may be due to competition for the enzyme cationic binding site.

Salicylic acid (SA), a weak inhibitor of the prostaglandin endoperoxide synthetase or fatty acid cyclooxygenase enzyme, is known to prevent irreversible enzyme inhibition by acetylsalicylic acid (ASA). The interaction of arachidonic acid with ferrous sulfate was used as a model to study the reaction of the fatty acid with the postulated enzymic cationic binding site on Fe2+-heme. SA was as potent as ASA in inhibiting the cooxygenation of arachidonic acid and ferrous sulfate. The results suggests that SA could complete effectively for the enzyme cationic site with ASA. Thus SA may block ASA acetylation of the cyclooxygenase by preventing ASA from binding to this site.

Arachidonic Acids↗
PubMed1981

A hypothesis for the mechanism of superoxide production by phagocytic cells.

When arachidonic acid is reacted with Fe2+, the Fe2+ is oxidized to Fe3+, and lipid peroxides are formed as detected by absorption at 232 nm. However, there is a large discrepancy between the amount of arachidonic acid converted to stable oxidized products and the amount of Fe2+ converted to Fe3+. We suggest that under appropriate conditions, electrons from the ferrous iron may reduce oxygen to superoxide in the presence of arachidonic acid. The results are consistent with evidence using bromophenacyl-bromide suggesting that release of fatty acids from cell phospholipids might be required for phagocytes to synthesize superoxide.

Animals↗