Search PubMed⌕ Search

Biomedical subjects

F Rossi

Publications and source records attributed to F Rossi.

At least 631 records · Page 35Linked to original sources
PubMed1985

Inhibition by verapamil of neutrophil responses to formylmethionylleucylphenylalanine and phorbol myristate acetate. Mechanisms involving Ca2+ changes, cyclic AMP and protein kinase C.

Verapamil inhibits in human neutrophils the respiratory burst, the secretion and the change of transmembrane potential induced by formylmethionylleucylphenylalanine, a Ca2+-dependent stimulus, and by phorbol myristate acetate, a Ca2+-independent stimulus. Besides the blocking of Ca2+ channels, many mechanisms are responsible for the inhibition of neutrophil responses. In fact, verapamil (i) increases the intracellular cAMP concentration, potentiates the cAMP response induced by the chemotactic peptide and induces the appearance of a cAMP response also when the stimulant is phorbol myristate acetate; (ii) causes a decrease of Ca2+ association to cell membranes, so depleting the pools of exchangeable Ca2+ and depressing the 'Ca2+ response' in terms of rise in [Ca2+]i monitored with Quin 2 and of rapid mobilization from cell membranes monitored by chlorotetracycline fluorescence change; (iii) inhibits the Ca2+-activated phospholipid-dependent protein kinase C. The data, discussed in relation to the biochemical mechanisms of the stimulus-response coupling, are compatible with the hypothesis of an involvement of the activation of protein kinase C as key step in the sequence of transduction events for the induction of many neutrophil functions.

Calcium↗
PubMed1985

Relationships between phosphoinositide metabolism, Ca2+ changes and respiratory burst in formyl-methionyl-leucyl-phenylalanine-stimulated human neutrophils. The breakdown of phosphoinositides is not involved in the rise of cytosolic free Ca2+.

The relationships between the changes of cellular Ca2+, the activation of phosphoinositide turnover and the functional responses induced by the stimulus-receptor interactions in neutrophils are matter of controversy. By measuring the concentration dependency of different formyl-leucyl-methionyl-phenylalanine (FMLP)-induced changes, the following values of ED50 were found: 1.6 and 0.8 nM for the rise in [Ca2+]i monitored with Quin-2, in the presence and absence of exogenous Ca2+, respectively; 20 nM for the activation of phosphoinositide metabolism, monitored as change in the 32Pi of phosphatidate; 14 nM for membrane-bound Ca2+ mobilization, monitored with chlorotetracycline (CTC); 34 nM for 45Ca2+ influx and 32 nM for the respiratory burst. Furthermore, low dose of FMLP causes an increase in [Ca2+]i in absence of activation of breakdown of phosphatidylinositol, phosphatidylinositol 4-monophosphate and phosphatidylinositol 4,5-biphosphate monitored as changes in [3H]glycerol radioactivity. The results clearly demonstrate that the increase in [Ca2+]i, due to the release from intracellular stores, is not caused by the breakdown of phosphatidylinositides. On the other hand, the data of the similarity of ED50 are compatible with an involvement of phosphoinositide response in the release of membrane bound Ca2+, monitored with CTC, and in the 45Ca influx and in the respiratory burst.

Aminoquinolines↗
PubMed1985

Intensity and kinetics of the respiratory burst of human neutrophils in relation to receptor occupancy and rate of occupation by formylmethionylleucylphenylalanine.

Studies on the relationship between the binding of fMet-Leu-Phe and the respiratory response in human neutrophils have been carried out under two different conditions of stimulus presentation, i.e., instantaneously and over a period of time. The main findings are as follows (1) Under the first condition the activation of the respiratory response reaches the maximum value very quickly, when the receptor occupancy is less than 20% that at equilibrium. After reaching this maximal value, the activated respiration progressively decreases, while the specific binding of the stimulant continues until equilibrium. (2) Under the second condition, i.e., when the stimulus to neutrophils is presented over a time of 1, 2 or 4 min, the respiratory response (and also the secretory one) is depressed or absent, and the initial rate of the binding (initial Vass) is lower, but the maximal values of the receptor occupancy at equilibrium and of the rate of receptor occupation (maximal Vass) are similar and only slightly lower than those reached under the condition of instantaneous presentation of the stimulus. (3) This form of desensitization is specific for fMet-Leu-Phe and does not consist of the inactivation of the target (NADPH oxidase), since neutrophils desensitized by the slow presentation of the peptide are able to respond to a second challenge with other stimulants. These results indicate that: (1) the efficacy of the stimulus-receptor complexes is short-lived; (2) the intensity of the respiratory response is dependent on the rate of reaching a threshold of binding; (3) when this initial rate is slow, owing to the slow presentation of the stimulus, a specific desensitization takes place, indicating the existence of a molecular mechanism, linked in some way to the initial rate of binding, that modulates the capacity of the stimulus-receptor complexes to transduce signals for cell responses. The physiological role of this type of desensitization is discussed.

Adult↗
PubMed1985

Mechanism of desensitization of neutrophil response to N-formylmethionylleucylphenylalanine by slow rate of receptor occupancy. Studies on changes in Ca2+ concentration and phosphatidylinositol turnover.

Previous studies on the regulation of responses of neutrophils to fMet-Leu-Phe have demonstrated the relevance of the role of the rate of occupation of the receptors by the stimulant. When this rate is decreased by presenting the peptide to neutrophils over a period of time by means of an infusion pump, the activation of the respiratory burst and of the secretion is greatly depressed or is absent. This paper deals with further investigations on the mechanisms of this desensitization, which previous results have shown to consist of an uncoupling between the ligand-receptor complexes and the target for cell responses, caused by the deceleration of the initial rate of occupation of the receptors. The data presented here demonstrate that this desensitization is not linked to the formation of a negative intermediate such as cAMP, but is associated with: (i) a depression of the rate and magnitude of the phosphatidylinositol response (activation of phosphatidylinositol turnover measured as modification of incorporation of [32P]Pi and [3H]glycerol into phosphatidylinositol and phosphatidic acid); (ii) a deceleration of the rate of the release of bound Ca2+, without a decrease in the total quantity of Ca2+ liberated (measured as fluorescence changes of chlorotetracycline treated neutrophils); (iii) a slower rise of cytosolic free Ca2+ concentration [Ca2+]i, without a decrease in the magnitude of the final increase of [Ca2+]i (monitored with Quin 2). These findings, which are discussed in relation to the recent hypotheses on the transduction reactions of receptor-mediated stimuli for neutrophil responses, are consistent with a mechanism of desensitization involving decreased production of diacylglycerol by the hydrolysis of phosphatidylinositol and deficient activation of Ca2+-phospholipid-dependent protein kinase C.

Adult↗
PubMed1985

Independence with respect to Ca2+ changes of the neutrophil respiratory and secretory response to exogenous phospholipase C and possible involvement of diacylglycerol and protein kinase C.

Exogenous phospholipase C induces in human neutrophils the activation of a respiratory burst, measured as O2 consumption and O-2 production, and of secretion of specific granules, measured as release of vitamin B-12 binding protein. The secretory response is minimal and follows the onset of the respiratory response. Studies carried out using cells prelabeled with [3H]glycerol and 32P on the molecular mechanism of the stimulations demonstrate that the effects are dependent on the formation of diacylglycerol by hydrolysis of different classes of glycerophospholipids. They are, however, independent of the activation of a 'phosphoinositide turnover' as occurs in cells stimulated with fMet-Leu-Phe. Furthermore, the respiratory and secretory responses to exogenous phospholipase C are not associated with modifications of cytosolic Ca2+ concentration, measured with the Quin-2 method, and of the release of bound Ca2+, measured with the membrane probe, chlorotetracycline. Apart from a quantitative difference, mostly regarding the ratio of the intensity of the respiratory and secretory responses, the effects caused by exogenous phospholipase C are qualitatively similar to those induced by phorbol myristate acetate and are probably linked to an involvement of protein kinase C, activated by diacylglycerol liberated in the plasma membrane.

Calcium↗
PubMed1985

Research on heterocyclic compounds. XVIII. Imidazo[2,1-b]-1,3,4-thiadiazole derivatives.

The synthesis of a series of 6-carbethoxy-, 6-carbethoxy-methyl-, and 5-carbethoxy-6-methylimidazo[2,1-b]-1,3,4-thiadiazoles was accomplished by reacting some 2-amino-1,3,4-thiadiazoles with ethyl bromopyruvate, 4-chloroacetoacetate, and 2-chloroacetoacetate, respectively; such carbethoxy derivatives afforded the corresponding carboxylic acids by hydrolysis. The antiinflammatory, analgesic, antipyretic and ulcerogenic activities were studied on three of the new acidic compounds.

Animals↗
PubMed1985

Aminoethers of (+)-1,3,3-trimethyl-2-oxabicyclo[2.2.2]octan-6-hydroxyimine with hypotensive activity.

The synthesis of beta-dialkylaminoethyl ethers (II a-f) and gamma-dialkylaminopropyl ethers (II g-i), as well as of aryl carbamates (III 1, m), starting from (+)-1,3,3-trimethyl-2-oxabicyclo[2.2.2]octan-6-hydroxyimine (I), is described. beta-Dimethylaminoethyl ether (II a) showed a remarkable hypotensive and bradycardic activity in rats; moreover, nearly all compounds (II) and (III) exhibited a weak antiarrhythmic activity in rats. Infiltration anesthesia in mice, beta-blocking activity in dogs and antiacetylcholine activity in vitro are also reported.

Acetylcholine↗
PubMed1985

Cardiovascular effects of tetanus toxin after systemic and intraventricular administration in rats.

A single intraperitoneal injection of tetanus toxin (50,100 and 200 minimum lethal dose per rat) produced a significant and dose-dependent increase in systemic blood pressure and heart rate in conscious rats. On the contrary, tetanus toxin, given directly into the third cerebral ventricle (20 and 40 minimum lethal dose), produced a gradual and dose-dependent decrease in blood pressure accompanied by bradycardia. In conclusion, the present findings show that tetanus toxin is able to affect cardiovascular activity and it is suggested that this may be due to an interference with central GABAergic mechanisms.

Animals↗
PubMed1985

Mechanisms and functions of the oxygen radicals producing respiration of phagocytes.

Respiratory burst is due to the activation of a membrane bound NADPH oxidase induced by perturbation of the plasma membrane during phagocytosis or following interaction between the cell surface and a number of environmental stimuli. It refers to the increase in the non-mitochondrial O2 consumption with a concomitant production of different reactive species (superoxide anion, hydrogen peroxide, hydroxyl radical, singlet oxygen ...). The effects of the respiratory burst depend on the intensity and combination of the different actions which are defensive, toxic, activatory and modulatory of the inflammatory process.

Animals↗
PubMed1985

Mechanism of production of toxic oxygen radicals by granulocytes and macrophages and their function in the inflammatory process.

The paper deals with 1) the features of the respiratory burst (increase of the respiration with production of O2 metabolites, O2-, H2O2, OH) of the inflammatory cells; 2) the factors responsible for its activation; 3) the methods for its measurement; 4) the molecular events which take place at the level of the plasma membrane following the interaction between the stimuli and the cell surface (the Ca++ changes, the modification of membrane potential, the activation of phospholipid turnover) and the hypothesis of the activation of the protein kinase C; 5) the nature of the NADPH oxidase whose activation is responsible for the respiratory burst and the production of O2 metabolites; 6) the defensive, toxic, proinflammatory and modulatory effects due to the reactivity of the oxygen metabolites.

Animals↗
PubMed1985

Studies on the nature and activation of O2(-)-forming NADPH oxidase of leukocytes. Identification of a phosphorylated component of the active enzyme.

Highly active superoxide (O2-)-forming NADPH oxidase was extracted from plasmamembranes of phorbol-12-myristate-13-acetate-activated pig neutrophils and was partially purified by gel filtration chromatography. Oxidase activity copurified with cytochrome b-245 in an aggregate containing phospholipids and was almost completely separated from FAD and NAD(P)H-cytochrome c reductase. A polypeptide with molecular weight of 31,500 strictly paralleled the purification of NADPH oxidase, suggesting that it is a major component of the enzyme. The enzyme complex was then dissociated by high detergent and salt concentration and cytochrome b-245 was isolated by a further gel filtration chromatography, with a 147 fold purification with respect to the initial preparation. The cytochrome b-245 showed a 31,500 molecular weight by SDS electrophoresis, indicating that it is actually the component previously identified in the partially purified enzyme. The 31,500 protein was phosphorylated in enzyme preparations from activated but not from resting neutrophils, suggesting that phosphorylation of cytochrome b-245 is involved in the activation mechanism of the O2(-) -forming enzyme responsible for the respiratory burst in phagocytes.

Animals↗