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Intact washed human platelets were studied for ecto-ATPase activity; labelled and unlabelled substrate was used. Strong activity was found with ATP and ITP; weaker activity occurred with ADP, UTP, and GTP. The K m of the ATP-splitting reaction was 1.6–2.0 × 10 −5 m . The enzyme was found to be Ca ++ - and Mg ++ -dependent, was blocked by EDTA, and had maximal activity in a pH range of 7.0–8.5. The enzyme was competitively inhibited by ADP. KCN, 1 × 10 −2 m , 5 × 10 −4 m ouabain, and 3 × 10 −2 m arginine methyl ester had no effect. The ecto-ATPase has many features in common with thrombosthenin, the contractile protein of platelets. The K m of purified thrombosthenin was 2.4 × 10 −5 m . Subcellular fractionation of platelets yielded a membrane fraction whose K m in the presence of ouabain was 1.8 × 10 −6 m . Antisera to thrombosthenin inhibited the platelet ecto-ATPase. The possible relationship of this enzyme to the mechanism of ADP-induced platelet aggregation is discussed.

SummaryAddition of ADP-8-C14 to platelet-rich plasma results in platelet radioactivity through a series of temperature-dependent reactions involving stepwise dephosphorylation of the nucleotide in plasma and then incorporation of the adenosine residue by the platelet, where it participates as a precursor in synthesis of platelet adenine nucleotides. This sequence of events, which requires a heat-labile nondialysable plasma factor, is blocked by 0.01 M KCN, by EDTA, by arginine methyl ester, by adenosine, and by AMP.ADP-induced platelet aggregation does not require the reactions outlined above and proceeds without ADP - breakdown and without binding of the ADP- molecule to the platelet. A possible mechanism of this phenomenon is suggested.

SummaryAfter incubation of platelet-rich plasma with labelled adenosine or ADP, platelet incorporation of radioactivity was assessed. Platelets were rapidly separated for counting by filtration through cellulose acetate Millipore. Inulin-H3 served as a plasma marker, and triple isotope techniques permitted simultaneous assessment of the behavior of the adenine and phosphate moieties of ADP without washing of platelets. In other experiments, electron microscopic radioautography was employed to trace the label after platelet incorporation.The results were consistent with previous reports that ADP is dephosphorylated in plasma and is incorporated by platelets only as a dephosphorylated residue, probably adenosine. The label crossed the platelet membrane and entered the platelet, where it was distributed in platelet granules and the agranular cell sap. Concentration within granules occurred to a minor degree.The results support the hypothesis that platelet aggregation by ADP occurs without a persistent bond of ADP to the platelet. Inhibition of aggregation by adenosine probably depends on a metabolic or transport process rather than on competition between adenosine and ADP for platelet binding sites.

SummaryPlatelet adhesiveness, measured by an in vitro technique, has been found abnormal in 21 of 24 patients with chronic renal failure. This abnormality was strongly correlated with prolongation of the Ivy bleeding time, with abnormal prothrombin consumption, and with clinical bleeding.The possible pathogenesis of this defect is discussed.

1.1. The literature on dermatitis due to celery has been reviewed. 2.2. Seventy-seven cases of dermatitis in celery workers have been observed. 3.3. The results of skin tests made by the scratch, intradermal, and patch methods, using various preparations from the celery plant, have been described. 4.4. The dermatitis is of the contact type and appears to be due to the oil in the celery plant. Dextro-limonene may be a factor in this oil. 5.5. The methods of treatment are discussed. In a pilot experiment two highly sensitive workers have been protected by injections of the celery oil.

Normal human washed erythrocytes were incubated in autologous plasma with 3 2P for varying periods of time. 2,3-Bisphosphoglyceric acid the major organic phosphate ester of red cells, was first isolated and purified by anion-exchange chromatography; subsequently, the C-2 Pi was selectively hydrolyzed by a molybdate-catalyzed reaction. The C-2-bound Pi of 2,3-P2-glyceric acid was found to have a significantly higher specific activity than C-3 Pi. Intramolecular equilibration was not reached until the 180-min incubation. No evidence of overhydrolysis or internal randomization by the molybdate reaction was noted which was confirmed following hydrolysis of double-label 2,3-P2-glyceric acid3 2P C-2, 3 3P C-3.

SummaryNormal washed human erythrocytes, when incubated in a buffered saline solution (pH 7.5-7.6) with T4 (3.75 X 10-8 M), demonstrated increased production of 2, 3-DPG and glucose consumption during the first 30 min of incubation. However, lactate production and ATP levels were decreased. The mechanism is probably related to a direct effect of T4 on the diphosphoglycerate mutase.

Thoracic ganglia and cercal nerve preparations from Periplaneta americana were exposed to Latrodectus mactans tredecimguttatus venom and to its toxic protein fractions which had been electrophoretically separated. Permanent block of endogenous activity of the thoracic ganglia was observed with crude venom at a concentration of 40 μg of protein per ml, while a tenfold concentration was required to block cercal nerve preparations. The separated proteins, which were found to be toxic in vivo, induced the same effect at lower concentrations. Blocked activity may be reversed following contact with the antivenin serum.

ALTERATIONS in the intracellular concentration of cyclic 3′,5′-AMP have been implicated in the action of many hormones and pharmacological agents in a variety of tissues1. In many cases, drugs, the action of which in liver, myocardium, adrenal and other tissues has been attributed to their effects on cyclic AMP concentrations, are known to influence aggregation of blood platelets, for example, platelet aggregation is inhibited by methyl xanthines2 and reserpine3, which inhibit cyclic nucleotide phosphodiesterase4,5, and is augmented by epinephrine6, which stimulates adenyl cyclase in liver, fat cells and myocardium7. 5-Hydroxytryptamine induces platelet aggregation8; it stimulates adenyl cyclase in the liver fluke9. Prostaglandin PGE1 is a potent inhibitor of platelet clumping10; it increases the level of cyclic AMP in adipose tissue11 but in some circumstances may lower its concentration in isolated fat cells1.