J. Pečivová

Evidence for intracellular histamine liberation in isolated rat mast cells

The beta-adrenoceptor blocking drug exaprolol liberated histamine from isolated rat mast cells in a dose- and time-dependent way. Histamine was liberated within seconds and was not followed by a parallel granule liberation. The inhibition of histamine liberation was induced with low temperature, low pH, high concentration of Ca2+, TTD, suramin and EDTA. Subcellular distribution of3H-exaprolol demonstrated a quantitative relationship between histamine depletion against exaprolol uptake in isolated rat mast cell granules. A nonspecific mechanism of action in the effect of exaprolol on mast cells is discussed. It is proposed that the drug acts on mast cells due to the direct and indirect ion exchange mechanism resulted in disproportion between histamine and granule liberation.

Effect of chloroquine on isolated mast cells

Chloroquine liberated a relatively low amount of histamine from isolated rat mast cells. In a dose-dependent way, this drug inhibited histamine liberation from mast cells stimulated with compound 48/80, A23187, concanavalin A plus phosphatidylserine (Con A+PS) and abolished histamine liberation induced by exaprolol. The degranulation was decreased in cells stimulated with 48/80, Con A+PS and exaprolol. Chloroquine significantly inhibited the formation of thromboxane B2 in mast cells stimulated with 48/80, Con A+PS and A23187. We assume that chloroquine interferes with mast cells at a plasmic membrane site as well as intracellularly.

On the interaction of beta-adrenoceptor-blocking drugs with isolated mast cells

The interaction of beta-adrenoceptor blocking drugs (BAB drugs) with isolated mast cells resulted. according to the compound, in either a liberation of biogenic amines or an inhibition of stimulated amine release. The liberatory drugs exaprolol and Kö 1124 decreased the level of cAMP, stimulated the activity of cyclic nucleotide-phosphodiesterase, decreased the incorporation of orthophosphate into membrane phospholipids and rapidly displaced calcium from binding sites in mast cells. The inhibitory drugs alprenolol, metipranolol, oxprenolol, practolol and propranolol, possessing lower liposolubility, produced opposite effects. Drugs from both groups displaced histamine from binding sites in isolated mast cell granules. The interaction of BAB drugs with mast cells is a result of non-specific rather than specific receptor interactions. Inhibitory drugs interfere with mast cells at membrane sites while liberatory drugs penetrate the membrane, thus acting both at the level of the membrane and intracellularly.

On the relationship between incorporation of32P into phospholipids and binding of beta-adrenoceptor blocking drugs to isolated mast cells

The lipophilic beta-adrenoceptor blocking drugs exaprolol and propranolol significantly decreased the incorporation of32P into phosphatidylethanolamine, phosphatidylcholine and phosphatidylinositol of isolated rat mast cells. In contrast, the hydrophilic drugs metipranolol, practolol and atenolol increased the incorporation of32P into phosphatidylethanolamine, phosphatidylserine and phosphatidylinositol. The inhibition of32P incorporation by lipophilic drugs correlated with the high binding of these drugs to mast cells.

Membrane perturbing activity of beta-adrenoceptor blocking drugs in isolated rat mast cells

Beta-adrenoceptor blocking (BAB) drugs perturb the membranes of isolated rat mast cells. Membrane fluidisation was temperature dependent and was determined by the liposolubility of the BAB drugs. The secretory index, evaluated as the ratio between histamine liberation and degranulation, correlated with the membrane order parameter of the mast cell membranes. The rank order of potency for mast cell activation and membrane fluidisation was: exaprolol > propranolol > metipranolol > atenolol.

Quercetin inhibits degranulation and superoxide generation in PMA stimulated neutrophils

Abstract Activated neutrophils represent the main source of myeloperoxidase (MPO), superoxide (SO) and subsequently derived oxygen metabolites. They have important microbicidal activities, however in inflammatory conditions they may secondarily attack surrounding tissues. Overproduction of reactive oxygen species, prolonged or excessive liberation of MPO and other effective yet also toxic substances from neutrophils may participate in disturbed apoptosis, intensify the inflammatory processes and result in serious human diseases. The inhibitory effect of quercetin on PMA stimulated SO generation in isolated human neutrophils was found to be dosedependent, without affecting the activity of intact isolated neutrophils. At comparable conditions, quercetin was more potent in inhibiting MPO release than SO generation. Our results indicate that quercetin could support resolution of inflammation through decreased activity of neutrophils, i.e. respiratory burst and degranulation.

Histamine liberation as a result of nonreceptor interaction

The highly lipophilic drug exaprolol liberates histamine from isolated mast cells and decreases the uptake of extracellular histamine in a dose-dependent manner. Intracellular histamine depletion was confirmed by electron microscopy and was accompanied by calcium displacement from intracellular storage sites. The significant decrease in membrane fluidity due to exaprolol was temperature-dependent and was most probably a result of its high membrane affinity and intracellular penetration. Membrane perturbation by exaprolol may account for this nonreceptor interaction. This could contribute to the understanding of adverse reactions to betaadrenoceptor blocking drugs.

Effect of beta-adrenoceptor blocking drugs on32P incorporation into and arachidonic acid liberation from phospholipids in stimulated rat mast cells

The lipophilic beta-adrenoceptor blocking (BAB) drugs metipranolol, propranolol and exaprolol significantly decreased 48/80-and A23187-induced32P incorporation into rat mast cell phospholipids. Exaprolol was the most active, followed by propranolol and metipranolol. Atenolol and metipranolol significantly decreased the 48/80-stimulated, and metipranolol and exaprolol the A23187-stimulated3H-arachidonic acid liberation from isolated mast cells.

Histamine liberation and membrane fluidisation of mast cells exposed to the beta-adrenoceptor blocking drug propranolol

Propranolol liberates histamine from isolated mast cells and decreases the uptake of extracellular histamine in a dose-dependent way. Histamine liberation due to propranolol is accompanied by calcium displacement from intracellular storage sites. The significant increase in membrane fluidity due to propranolol is temperature dependent. The perturbation of membranes is most probably the explanation of propranolols interaction with isolated rat mast cells which results in altered histamine transportation.

Quantitative correlation between histamine and35S release from isolated rat mast cells due to the beta-adrenergic blocking drug Kö 1124

An attempt was made to explain the mechanism of histamine release from isolated rat mast cells induced by the beta-adrenergic blocking drug Kö 1124. This drug at the highest concentration used released 12 times more histamine than most other investigated beta-blockers. The release of histamine with Kö 1124 was dose and temperature dependent. The maximal histamine release was at pH 8 and in the absence of calcium ions. Increased calcium concentration decreased histamine release significantly. The effect of Kö 1124 on histamine release from mast cells was inhibited only by cocaine and 2,4-dinitrophenol; other metabolic inhibitors were ineffective. The histamine release due to Kö 1124 was not followed by an equal release of35S. Isoprenaline in equimolar concentration decreased histamine release induced by Kö 1124 significantly. The release of35S-labelled granules was decreased or blocked by isoprenaline.