calcimycin and 1-10-phenanthroline

Inhibitors of metalloendopeptidases interfere with events involving Ca2(+)-dependent membrane fusion in a number of cell types. The divalent ion chelating agent 1,10-phenanthroline inhibited pancreatic amylase secretion stimulated by carbachol, cholecystokinin-octapeptide (CCK-8), or bombesin, but detailed studies indicated that this is unlikely to be a result of inhibition of metalloendopeptidase activity. The binding of [3H]N-methylscopolamine to pancreatic acini was reduced by 1,10-phenanthroline and this would explain the marked inhibition of carbachol-induced amylase secretion by the chelating agent. CCK-8-stimulated hydrolysis of phosphatidylinositol-4,5-bisphosphate was reduced by 1,10-phenanthroline while the binding of CCK-8 to acini was not affected. This inhibition of hydrolysis would explain the inhibition of CCK-8- and bombesin-induced amylase secretion. The metalloendopeptidase substrate carbobenzoxyglycylphenylalanylamide did not affect bombesin-stimulated amylase secretion. Amylase secretion evoked by treating pancreatic acini with the ionophore A23187 or dibutyryl-cyclic AMP was not reduced by 1,10-phenanthroline, indicating a lack of involvement of metalloendopeptidases in the process of exocytosis in this cell type.

Topics: Amylases; Animals; Bombesin; Bucladesine; Calcimycin; Carbachol; Dipeptides; Metalloendopeptidases; Mice; N-Methylscopolamine; Pancreas; Phenanthrolines; Phosphatidylinositol 4,5-Diphosphate; Phosphatidylinositols; Receptors, Muscarinic; Scopolamine Derivatives; Sincalide

The effects of doxorubicin and its primary metabolite doxorubicinol on the polymorphonuclear leukocyte (PMNL) respiratory burst were studied using lucigenin and luminol for detection of oxygen metabolite generation. Although both anthracyclines inhibited PMNL activation at concentrations achieved with therapeutic administration of doxorubicin, doxorubicinol was much more potent than doxorubicin. Preincubation of PMNL with either drug caused a persistent inhibition of cell function after drug washout that was not prevented by inclusion of either free radical scavengers or iron chelators in the incubation medium. Although complete suppression of the PMNL respiratory burst occurred with concentrations of doxorubicinol greater than 0.3 microgram/ml, a marked potentiation of the response was observed at lower concentrations (0.01 or 0.03 microgram/ml) of the same drug. Potentiation occurred only when albumin was present in the reaction medium, was eliminated by iron chelators, was not observed after PMNL incubation with drug and was dependent upon the activating agent. In contrast to doxorubicinol, doxorubicin did not potentiate the PMNL respiratory burst. These results demonstrate potent effects of doxorubicinol on PMNL oxygen metabolite generation that are markedly greater in degree and different in character than those of doxorubicin. Because both inhibitory and enhancing effects are apparent at concentrations of doxorubicinol achieved in vivo, this metabolite may be important in the clinically observed toxicity of doxorubicin.

Topics: Adult; Calcimycin; Deferoxamine; Doxorubicin; Humans; Luminescent Measurements; Luminol; Middle Aged; Neutrophils; Oxygen Consumption; Phenanthrolines

Exocytosis is initiated by the receptor-mediated influx of calcium that results in fusion of the secretory vesicle with the plasma membrane. We examined the possibility that calcium-dependent exocytosis in mast cells and adrenal chromaffin cells requires metalloendoprotease activity. Metalloendoprotease inhibitors and dipeptide substrates block exocytosis in these cells with the same specificity and dose dependency as that with which they interact with metalloendoproteases. Metalloendoprotease activity is identified in these cells with fluorogenic synthetic substrates, which also blocked exocytosis. Metalloendoprotease activity is highest in the plasma membrane of chromaffin cells. The metalloendoprotease appears to be required in exocytosis at a step dependent on or after calcium entry, since exocytosis initiated by direct calcium introduction in both mast cells and chromaffin cells is blocked by metalloendoprotease inhibitors.

Topics: Adrenal Glands; Animals; Calcimycin; Calcium; Cattle; Cell Membrane; Chromaffin System; Concanavalin A; Dipeptides; Endopeptidases; Exocytosis; Female; Histamine Release; Mast Cells; Metalloendopeptidases; Oligopeptides; Phenanthrolines; Protease Inhibitors; Rats; Rats, Inbred Strains