Phospholipid methylation and biological signal transmission

Mammalian beta-adrenoceptors: concomitant biospecific elution with protein kinase activity from Sepharose-alprenolol

The mammalian beta-adrenoceptors were solubilized from crude guinea pig lung membranes with the plant glycoside digitonin. The solubilized receptors were absorbed by affinity gels with (+/-)alprenolol as ligand and could be eluted biospecifically in good yield with either agonists or antagonists. A more than 100-fold purification can be achieved in a one-step procedure. Antagonist-eluted beta-adrenoceptors have affinities for antagonists similar to those of particulate or solubilized receptors. Their binding constants for agonists, however, are comparable to those of the particulate receptor. A cAMP-independent protein kinase activity was eluting concomitantly with the beta-adrenoceptors. The protein kinase phosphorylated endogenous substrates with 50 000 and greater than 150 000 subunit molecular weight.

Allergen tachyphylaxis of guinea pigs in vivo; a prostaglandin E mediated phenomenon?

Ovalbumin (OA) sensitized guinea pigs were repeatedly challenged with 1% OA in saline nebulized ultrasonically at the 0, 10, 20, 60 and 70th min. The intensity of bronchial obstruction was measured by body plethysmography. The first three challenges (0. 10, 20 min) caused strong asthmatic reactions in all animals, the last two (60, 70 min) only mild one in 10 out of 15 animals. The development of this "tachyphylaxis" was markedly reduced by pretreatment of the animals with cyclooxygenase inhibitors (indomethacin 10 mg/kg intraperitoneally resp, acetylsalicylic acid 10 mg/kg orally 2 h before tests). The effect of both inhibitors (i.e. inhibition of tachyphylaxis) was abolished by supplementing prostaglandin E2 as aerosol simultaneously to the allergen (100-200 ng per inhalation). The results suggest that allergen tachyphylaxis we have observed in vivo might be due to synthesis of cyclooxygenase products, e.g. prostaglandin E.

Heberden Oration 1980: aspects of the cell biology of the rheumatoid synovial lesion

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Inhibition of the hamster sperm acrosome reaction by transmethylation inhibitors

Two inhibitors of somatic cell transmethylation, homocysteine thiolactone (Hcy) and 3--deazadenosine (3--DZA), inhibited the acrosome reactions of hamster sperm in vitro. Hcy (250 microM) or 3--DZA (200 microM) inhibited acrosome reactions by approximately 30% after 4 hours of incubation with washed sperm in a capacitating medium containing epinephrine, taurine, and bovine serum albumin. Inhibition by 3--DZA decreased by 5 hours, but inhibition by Hcy did not. Incubation of sperm with the combination of both inhibitors inhibited acrosome reactions by nearly 60% at 4 hours, and did not appreciably decrease with time up to 5 hours. These results are the first to demonstrate that such inhibitors can interfere with the acrosome reaction and taken together with the effects of Hcy and 3--DZA on somatic cells, suggest that sperm protein and/or phospholipid transmethylation is/are involved in capacitation and/or the acrosome reaction.

Molecular and cellular mechanisms of leukocyte chemotaxis

The application of modern scientific methods to the study of leukocyte function has begun to reveal the molecular and cytostructural bases of the chemotactic responses of these cells. Leukocyte chemotaxis is initiated by the binding of chemoattractants to distinct plasma membrane receptors; this finding alters transmembrane potential and activates ionic fluxes. The subsequent sequence of metabolic processes leads to a rearrangement of cytoskeletal elements that is manifested by orientation and migration of the cells toward the source of the chemotactic gradient.

Microsomal phosphatidylethanolamine methyltransferase: inhibition by S-adenosylhomocysteine

Inhibition by S-adenosylhomocysteine (AdoHcy) of the three reactions of phosphatidylethanolamine methyltransferase which catalyzes the production of phosphatidylcholine from phosphatidylethanolamine in guinea pig and rat liver microsomes has been evaluated. Five of the six methylation reactions in these two species exhibit greater affinity for inhibitor, AdoHcy, than for substrate, S-adenosylmethionine (AdoMet). The Ki values for the rate-limiting reactions were 3.8 microM and 68 microM in rat and guinea pig livers, respectively. An AdoMet : AdoHcy ratio of 12 : 1 in developing liver was found to decline to a constant value in the adult of 5 : 1. The concentration of AdoHcy in rat and guinea pig liver increases markedly following death of the animal. A concomitant decrease in the AdoMet level was observed in guinea pig liver. A comparison of phosphatidylethanolamine methyltransferase activity with the hepatic concentrations of AdoMet and AdoHcy in mouse, rat, rabbit and guinea pig is presented. Regulation of the methylation pathway is discussed.

Glucose-insulin-potassium induced alterations in individual plasma free fatty acids in patients with acute myocardial infarction

Total and individual plasma free fatty acids (FFA) were measured on admission and over the next 4 days in 24 patients admitted to the hospital with chest pain and suspected acute myocardial infarction (AMI). In a prospective randomized fashion, the patients were either given an infusion of 300 gm of glucose, 50 units of insulin, and 80 mEq of KCl per liter at a rate of 1.5 ml/kg/hr over the initial 48 hours of hospitalization, or they served as controls receiving conventional therapy. Eleven patients were in the control group and 13 were in the glucose-insulin-potassium (G-I-K) group. Twenty-one of the patients had an AMI by CK-MB rise and ECG changes (in the G-I-K group three did not evolve AMI). The total plasma FFA were 840 +/- 134 microM/L in the controls and 933 +/- 160 microM/L in the G-I-K group initially (prestudy). Total FFA rapidly fell in the G-I-K group and then rebounded when G-I-K was stopped. In contrast, total FFA values fell gradually in the control group over the 4-day period. The individual FFA had similar percentages initially in the two groups. In the control group the percent of individual plasma FFA was unchanged over the period studied, although there was some mild random day-to-day fluctuation. In contrast in the G-I-K group linoleic acid fell both during and after the infusion was stopped (26.8% to 19.1% P less than 0.001). Arachidonic acid doubled in percentage of the total FFA value during G-I-K infusion (3.1% to 6.5%, P less than 0.002) and returned to the control value when it was stopped. Thus G-I-K infusion during AMI reduces the total level of plasma FFA while increasing the percent of arachidonic and decreasing the percent of linoleic acid, observations proposed to reflect improved membrane stability of the ischemic myocardium.

Mechanisms of slow postsynaptic potentials

Classical views of synaptic transmission have to be modified to take account of slow postsynaptic potentials (p.s.ps), which are often mediated by novel ionic and molecular mechanisms and which are sometimes evoked by neuropeptides. Understanding slow p.s.ps will provide insights into the mechanisms of biological signal transduction and long-term signalling in the nervous system.

Phospholipid methylation and phospholipase A2 activation in cytotoxicity by human natural killer cells

The role of phospholipid methylation and phospholipase A2 (phosphatide 2-acylhydrolase, EC 3.1.1.4) in natural killer (NK) function by human peripheral blood mononuclear cells was studied. Pretreatment of effector cells with a methyltransferase inhibitor, 3-deazaadenosine, in the presence of homocysteine thiolactone, reduced cytotoxicity in a dose-dependent fashion. This effect was closely associated with inhibition of methylation of lipids but not of nucleic acids or proteins. The suggestion for a role of phospholipid methylation was supported by the observation that the interaction between NK-susceptible tumor targets and peripheral blood mononuclear cells caused increased phospholipid methylation only when susceptible target cells were used. Phospholipase A2 was also implicated in human NK activity. Inhibitors of the enzyme such as tetracaine, mepacrine, Rosenthal's inhibitor, and corticosteroids impaired NK function. Rosenthal's inhibitor was also shown to exert an inhibitory effect on a purified NK-cell population obtained by the isolation of large granular lymphocytes on Percoll gradients. Peripheral blood mononuclear cells were also directly shown to display phospholipase A2-like activity, as measured by the decrease in radioactive arachidonate from prelabeled phospholipids, specifically phosphatidylcholine, in effector cells. These data suggest that enhanced phospholipid methylation occurs during the recognition function of NK cells. Consequent activation of phospholipase A2 might be involved in the mechanisms leading to lytic events within the target cell.

Metabolic basis for disorders of purine nucleotide degradation

Purine nucleotide degradation refers to a regulated series of reactions by which human purine ribonucleotides and deoxyribonucleotides are degraded to uric acid in humans. Two major types of disorders occur in this pathway. A block of degradation occurs with syndromes involving immune deficiency, myopathy or renal calculi. Increased degradation of nucleotides occurs with syndromes characterized by hyperuricemia and gout, renal calculi, anemia or acute hypoxia. Management of disorders of purine nucleotide degradation is dependent upon modifying the specific molecular pathology underlying each disease state.

Micromolar calcium stimulates proteolysis and glutamate binding in rat brain synaptic membranes

Incubation of cortical synaptic membranes with low concentrations of calcium resulted in a decrease in the amount of a high-molecular-weight doublet protein and an increase in the sodium-independent binding of glutamate. Both effects were blocked by the thiol protease inhibitor leupeptin. These results suggest that calcium-induced proteolysis of membrane components regulates the number of glutamate receptors in neuronal membranes.

Thromboxane may be important in the organ damage and hypotension of malaria

Generalized circulatory changes, manifesting as pulmonary oedema, acute renal failure, liver damage and severe hypotension, are well recognized aspects of acute falciparum malaria. The organ pathology is thought to be associated with a restricted local blood flow. These aspects of falciparum malaria are strikingly analogous to the shock syndrome which follows trauma, the injection of indotoxin, or some bacterial infections. Two of the cyclooxygenase products of arachidonic acid, thromboxane A2 and prostacyclin, acting through their opposing effects on vasoactivity and platelet aggregation, are emerging as the major controlling influences of vascular homeostasis. The effects of thromboxane, which constricts blood vessels and aggregates platelets, appear to dominate during traumatic or endotoxic shock. Thus thromboxane is potentially one of the main mediators of endotoxicity, and as such, from our previously published model, is likely to be important in the pathogenesis of the circulatory disturbances seen in acute malaria. This suggestion is consistent with earlier evidence that the autonomic nerve supply and bradykinin may have an important role in the pathogenesis of the haemodynamic changes in this disease. It also implies that pharmacological antagonists of thromboxane may provide useful specific therapy for the main life-threatening aspects of acute falciparum malaria.

Conversion of 3T3-L1 fibroblasts to fat cells by an inhibitor of methylation: effect of 3-deazaadenosine

3-Deazaadenosine, an inhibitor of methylation, increased the frequency of conversion of 3T3-L1 fibroblasts to fat cells in a dose-dependent manner. Once converted, the 3T3-L1 fat cells retained their adipose morphology and accumulated triglycerides even when 3-deazaadenosine was removed from the culture medium. 3-Deazaadenosine may perturb cellular methylation and thereby lead to an increase in the frequency of differentiation of 3T3-L1 fibroblasts to fat cells.