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B D Gomperts

Publications and source records attributed to B D Gomperts.

At least 73 records · Page 4Linked to original sources
PubMed1981

Rat mast cells permeabilized with ATP secrete histamine in response to calcium ions buffered in the micromolar range.

1. Rat mast cells with ATP (0.5-4 micro M) in the absence of divalent cations (so that almost all the ATP is present as ATP4-) became permeable to normally impermeant aqueous solutes, added extracellularly. These include the stable complexes Co HEDTA and Ca EDTA, and 6-carboxyfluorescein but not inulin. At 4 micro M-ATP4- the space accessible to Ca EDTA is 89% of that occupied by 3H2O. 2. The kinetics of solute entry are regulated by the concentration of ATP4-. 3. Ca2+, buffered in the range 1-10 micro M with HEDTA, causes histamine secretion from mast cells that have been rendered permeable with ATP4-. The extent of secretion increases as the concentration of ATP4- is raised from 3 to 5 micro M. With extracellular Ca2+ present as physiological (millimolar) concentrations, the effect of increasing ATP4- through this range is to inhibit secretion. 4. The rates of histamine secretion and of 32P-metabolite leakage from 32P-prelabelled cells in the presence of micromolar concentrations of Ca2+, were compared. The kinetics of both processes are regulated by the concentration of ATP4-, but not Ca2+.

Adenosine Triphosphate↗
PubMed1981

Inhibitory effects of natural flavonoids on secretion from mast cells and neutrophils.

30 natural flavonoids were tested for their inhibitory action on stimulated secretion from rat mast cells and rabbit neutrophils in vitro. There was no correlation between the degrees of inhibitory activity of the flavonoids on the two cell types, or upon the inhibition of the Ca2+ transporting ATPase from sarcoplasmic reticulum. The inhibitory action of flavonoids on mast cells is believed to be at the level of the receptor directed Ca2+ channels in the plasma membrane. For neutrophils it is demonstrated that inhibitory flavonoids do not significantly alter Ca2+ movements across the plasma membrane; nor do they reduce the extent of ligand binding to its receptor. This evidence suggests that flavonoids do not have a common mode of inhibition on these cell types. Rather, the flavonoids must have more specific effects on the different systems examined.

Animals↗
PubMed1980

Stimulus-secretion coupling in rabbit neutrophils is not mediated by phosphatidylinositol breakdown.

In common with other cells which use intracellular Ca2+ to mediate specific cell function, when rabbit neutrophils are stimulated with specific agonists the rate of metabolism of phosphatidylinositol (PI) increases. This is normally measured as the incorporation of radioactive phosphate or inositol into PI, but these reactions are presumed to be secondary processes following the initial breakdown of pre-existing PI to diacylglycerol. The radioactive labels are incorporated during the stepwise resynthesis of PI via phosphatidic acid (PA). It has been suggested that in the sequence of biochemical events, starting with the binding of the ligand to a receptor, and finally resulting in the expression of cellular activity, the breakdown of PI is an early event immediately directed by activation of the receptor. This could then control the increase in cytoplasmic Ca2+ and other processes dependent on this. Here we report an analysis of the temporal relationship between these phospholipid changes and cell stimulation. Our evidence suggests that in neutrophils, PI breakdown and PA labelling are both consequences and not causes of a rise in intracellular Ca2+.

Animals↗
PubMed1980

Use of cytochalasin B to distinguish between early and late events in neutrophil activation.

Cytochalasin B greatly enhances secretion of beta-glucuronidase and generation of superoxide on stimulation of rabbit peritoneal neutrophils with the soluble chemotactic factor N-formylmethionylleucylphenylalanine (f-Met-Leu-Phe). There are smaller changes due to cytochalasin B on binding of f-Met-Leu-[(3)H]-Phe, stimulation of phosphatidylinositol turnover and the stimulated increase in the permeability of the cell membrane to Ca(2+). These latter changes are probably artefactual and arise as secondary consequences of cell stimulation. Our observations support the notion that changes in Ca(2+) permeability of membranes and stimulation of phosphatidylinositol turnover reflect early stages in the sequence of events initiated by f-Met-Leu-Phe binding to its receptor and which lead to cell activation phenomena such as secretion and superoxide production.

Animals↗
PubMed1980

The ATP4- receptor of rat mast cells.

The concentration-dependence on exogenous ATP of activation and inhibition of mast-cell histamine secretion, phosphatidylinositol labelling and leakage of metabolites shows that all these functions are regulated by the free acid ATP4-. Maximal histamine secretion and phosphatidylinositol labelling occur with ATP4- at approx. 2 microM, but higher concentrations, which cause inhibition of secretion and phosphatidylinositol labelling, are required to maximize leakage of 32P-labelled metabolites. Both enhancement and inhibition of phosphatidylinositol labelling (due to low and high concentrations of ATP4- respectively) are rapid in onset; histamine secretion is characterized by a delay, especially at low concentrations of ATP4- (approx. 1 microM). Phosphatidylinositol labelling and histamine secretion are dependent on extracellular Ca2+. Metabolite leakage due to the presence of exogenous ATP4- is slow and does not require Ca2+. Of 18 analogues of ATP that were tested, only four were agonists for secretion, and only these four permitted leakage of 32P-labelled metabolites. It is argued that activation and inhibition of histamine secretion, phosphatidylinositol labelling and metabolite leakage are all initiated by ATP4- acting at the same receptor. For mast cells stimulated with ATP4- enhancement of phosphatidylinositol metabolism is not sufficient by itself to cause Ca2+-dependent secretion.

Adenosine Triphosphate↗
PubMed1980

Early events in the activation of Ca2+ dependent secretion: studies with rat peritoneal mast cells.

1. Secretion of histamine from mast cells is a Ca2+ dependent exocytotic process initiated by attachment of various agents to receptors on the cell surface. Secretion can also be triggered by the Ca2+ ionophores A23187 and ionomycin. Only in the case of the ionophores is the mechanism of Ca2+ mobilisation understood. 2. When agonist ligands are added to cells which have been preincubated with 32P-phosphate or 3H-inositol, one can detect an increase in the rate of labeling of phosphatidylinositol. As for other systems, the phosphatidylinositol response in mast cells shows the characteristics of an early receptor directed event. 3. We discuss the relationship of the phosphatidylinositol response and Ca2+ mobilisation in mast cell activation.

Animals↗
PubMed1979

Evidence for a role of phosphatidylinositol turnover in stimulus-secretion coupling. Studies with rat peritoneal mast cells.

Histamine secretion and phosphatidylinositol turnover were compared in antigen-sensitized rat peritoneal mast cells stimulated with a number of different ligands. A small and variable increase in the incorporation of [(32)P]P(i) and of [(3)H]inositol into phosphatidylinositol was observed when the cells were treated with immunoglobulin E-directed ligands (antigens and concanavalin A), and this was accompanied by a low amount of secretion (<10% of total cell histamine). In the presence of added phosphatidylserine, the addition of immunoglobulin E-directed ligands invariably led to an enhanced rate (approx. 4-fold) of labelling of phosphatidylinositol and, in the presence of Ca(2+), this was accompanied by the secretion of histamine. The labelling of phosphatidylinositol and histamine secretion were also stimulated by chymotrypsin and compound 48/80. Whereas the phosphatidylinositol response did not require the presence of extracellular Ca(2+), the secretion of histamine was either enhanced or dependent on extracellular Ca(2+) (depending on the ligand used). The dependence on ligand concentration for the phosphatidylinositol response and histamine secretion were similar. The increased isotopic incorporation into phosphatidylinositol continued for about 1h although histamine secretion (elicited with concanavalin A) stopped within 2min. These results support the proposition that metabolic events involving phosphatidylinositol play a necessary intermediate role in the regulation of Ca(2+) channels by ligand-activated receptors.

Animals↗
PubMed1979

Activation and inhibition of calcium-dependent histamine secretion by ATP ions applied to rat mast cells.

1. The concentration dependence on ATP of mast cell histamine secretion in the presence of various concentrations of Mg2+ and Ca2+ confirms that the agonist form of ATP is the free form of ATP (ATP(free) not bound to divalent cations, i.e. ATP4-. It induces 50% activation at about 1.2 microM, maximal secretion at about 2.7 microM and 50% self-inhibition at about 4.4 microM. 2. The divalent cations Mg2+ and Ca2+ were used to buffer ATP(tree) in the range 1-8 microM in the presence of much higher concentrations of ATP(total). In addition to its effect as a buffer for ATP, Ca2+ is required for secretion. 3. With ATP(free) at 1 microM, the time-course of histamine secretion is characterized by a delay of about 10 min before secretion commences. With increasing concentration of ATP(free) the delay becomes shorter (less than 5 min with ATP(free) at 2 microM). 4. Secretion commences promptly on addition of Ca2+ to cells which have been pretreated with low concentrations of ATP(free) (less than 2 microM). This observation suggests that the delay normally observed represents the time taken for Ca2+ sensitivity to develop (i.e. probably the time taken for Ca2+ channels to open). 5. Late addition of Ca2+ to cells pretreated with higher concentrations of ATP(free) (greater than 2 microM) results in a reduced amount of histamine secretion compared with that which normally occurs. This reduction (which increases with time of exposure to ATP) and the self-inhibition due to higher concentrations of ATP(free) may be two facets of a common inhibitory mechanism. 6. These results are discussed in the light of other experiments which show that mast cells treated with ATP(free) at self-inhibitory concentrations become permeable to phosphorylated metabolites and nucleotides.

Adenosine Triphosphate↗
PubMed1977

Mobile carrier ionophores for Fe(II).

A23187 and certain other carboxylate ionophores are capable of transferring Fe(II) but not Fe(III) across phospholipid bilayers (liposomes) and red cell membranes. A23187 is able to transfer Fe(II) from ferritin loaded liposomes when allied with a suitable redox couple and sink. The affinity of A23187 for Fe(II) is approximately five orders of magnitude greater than for Ca2+, as judged by two phase extraction techniques.

Calcimycin↗
PubMed1977

Quercetin: a novel inhibitor of Ca2+ influx and exocytosis in rat peritoneal mast cells.

The effect of the transport ATPase inhibitor, quercetin on histamine secretion from antigen sensitized mast cells was examined. At micromolar concentrations, quercetin had an immediate inhibitory effect on histamine secretion mediated by antigen, concanavalin A and ATP but it had little effect on release induced by the ionophores A23187 and X537A. Quercetin exerts its effect after the binding of the releasing ligands and the distinction between its effect on ligand induced and A23187 induced secretion suggests that it affects the normal path of Ca2+ entry into the cell. The inhibitory effects of quercetin were compared with those of the structurally related anti-allergic drugs cromoglycate and AH7725.

Adenosine Triphosphate↗
PubMed1975

Non-T cell-mediated cytolysis of antibody-coated sheep red blood cells requires Mg++ but not Ca++: An argument against a conventional "stimulus-secretion" mechanism for cytolysis.

"Stimulus-secretion" processes, and notably those in which the stimulus is provided by the formation of an antigen-antibody complex at the cell surface, require the presence of external Ca++. To test the possiblity that effector cells, in non-T cell mediated cytolysis, might be triggered to release a cytolytic product by a similar mechanism, we investigated the requirements of this phenomenon for divalent cations. We found that Ca++ is not sufficient, not necessary, and not inhibitory, whereas Mg++ is necessary and sufficient. Other cations were tested, and we found that Mn++ behaved like Mg++. The Ca++ data suggest that no conventional "stimulus-secretion" process is operative in non-T cell mediated cytolysis of antibody-coated sheep red blood cells.

Animals↗