Priming of human polymorphonuclear leukocytes with granulocyte-macrophage colony-stimulating factor involves protein kinase C rather than enhanced calcium mobilisation.

Pretreatment of human polymorphonuclear leukocytes with the recombinant human granulocyte-macrophage colony-stimulating factor (rhGM-CSF) enhances leukotriene biosynthesis in response to a receptor agonist (e.g. N-formyl-methionyl-leucyl-phenylalanine, fMLP) or a Ca(2+)-ionophore (e.g. ionomycin). This priming effect could be traced back to an elevated release of arachidonic acid from the phospholipid pools and hence an increased leukotriene biosynthesis by 5-lipoxygenase. Preincubation of polymorphonuclear leukocytes with GM-CSF did not influence the basal intracellular Ca2+ level and does not enhance cytosolic free calcium after stimulation with fMLP or ionomycin. Only a small increase in the second Ca2+ phase after receptor agonist stimulation was found. However, the Ca(2+)-threshold level necessary for the liberation of arachidonic acid by phospholipase A2 was decreased from 350-400 nM calcium in untreated cells to about 250 nM calcium in primed cells. This allows phospholipase A2 to be activated by a release of calcium from intracellular stores and by ionomycin concentrations which are ineffective in untreated cells. Protein biosynthesis inhibitors like actinomycin D (10 micrograms/ml) and cycloheximide (50 micrograms/ml) had no effect on the enhanced leukotriene biosynthesis in primed cells after stimulation with ionomycin. However, staurosporine (200 nM), an inhibitor of protein kinase C totally abolished the priming effect of GM-CSF after stimulation with ionomycin. The priming effect of GM-CSF could be mimicked by phorbol myristate acetate (PMA; 1 nM) and no additive or synergistic effect was found on leukotriene biosynthesis by simultaneous pretreatment with PMA and GM-CSF and stimulation with either fMLP or ionomycin. These results provide evidence that the enhanced arachidonic acid release in GM-CSF-primed polymorphonuclear leukocytes after stimulation with either fMLP or ionomycin involves activation of protein kinase C which, by a still unknown mechanism, reduces the Ca2+ requirement of phospholipase A2.     

Mikrorespirometrische Untersuchungen an höheren Pflanzen. I

Ohne ZusammenfassungMit 2 Textabbildungen.     

Aufkleben von Paraffinschnitten mit Ammoniakhaltiger Wasserglaslösung

Ohne Zusammenfassung     

Anion transport through the contraluminal cell membrane of renal proximal tubule. The influence of hydrophobicity and molecular charge distribution on the inhibitory activity of organic anions

Three different mechanisms of anion transport have been identified for the contraluminal membrane in the proximal tubule of the rat kidney. These mechanisms are specific for the transport of sulfate, dicarboxylate and p-aminohippurate anions. Sulfate transport is inhibited by bivalent organic anions with a distance between the charges of less than 7 A. The sulfate system acts in two modes: in a planar mode for anions with flat charged residues such as COO- and a charge separation of 3-4 A or in a bulky mode for groups such as SO3H- and a charge separation of 4-7 A. Monovalent anions can be accepted if there is a hydrophobic core next to the negative charges. Dicarboxylate transport is inhibited exclusively by anions with two charge centers located within 5 to 9 A, one of those possibly being a partial charge of -0.5 elementary charges. p-Aminohippurate transport is inhibited by monovalent anions, if these have a hydrophobic domain with a minimal length of about 4 A. Bivalent anions inhibit, if they have a charge distance of 6-10 A; both charges can be partial charges of about -0.5 elementary charges. Longer bivalent anions can be effective provided they have a sufficiently large hydrophobic domain. For the sulfate and p-aminohippurate systems it is found that anions with high acidity yield good inhibition. The overlapping specificities of the three systems with respect to charge distance and hydrophobicity allow them to accept a large variety of organic anions.