Growth factor-stimulated trans plasma membrane electron transport in HL-60 cells

Electron flow across the plasma membrane of living cells and its rapid modulation by growth factors has been measured continuously through a simple assay procedure whereby the transported electrons are captured by ascorbate free radical to slow the rate of chemical oxidation of ascorbate. The assay provides a direct demonstration of electron transport to an external electron acceptor that is both physiological and impermeant. The reduction of external ascorbate free radical is stimulated by the growth factors, EGF and transferrin, and is inhibited by wheat germ agglutinin. The results demonstrate, under physiological conditions, the operation of a growth factor- and lectin-responsive electron transport system at the cell surface using a cultured human cell line.

Immunocytolocalization of plasma-membrane H(+)-ATPase in maize coleoptiles and enclosed leaves

The plasma-membrane H(+)-ATPase (EC 3.6.1.35) of maize (Zea mays L.) coleoptiles and enclosed leaves has been localized at the optical-microscope level utilizing paraffin sections and a specific monoclonal antibody. Both in coleoptiles and in leaves the stomatal guard cells and the phloem of vascular bundles are the tissues most enriched in ATPase. The enrichment in guard cells is relevant to active ion transport during stomata opening. Considering the postulated activation of coleoptile ATPase by auxin, it is remarkable that the ATPase is not enriched in the coleoptile epidermis, where most of the auxin receptor is located.

Ascorbate is regenerated by HL-60 cells through the transplasmalemma redox system

Ascorbate was maintained in the media during a long-term culture by HL-60 cells. The chemical oxidation of ascorbate was reversed in vitro by living HL-60 cells and was related to the amount of cells added. The increase of NADH concentration by lactate addition to cells was accompanied by an increase of both ascorbate regeneration and ferricyanide reduction. Further, plasma membrane enriched fractions from HL-60 cells revealed enhancement of both ascorbate regeneration and ferricyanide reduction in the presence of NADH when previously treated with detergent. The blockage of cell surface carbohydrates by wheat germ agglutinin (WGA) and Concanavalina ensiformis (Con A) lectins significantly inhibited the regeneration of ascorbate caused by the cells. These results support the idea that ascorbate is externally regenerated by the NADH-ascorbate free radical reductase as a part of the transplasma membrane redox system.

Ascorbate free radical stimulates the growth of a human promyelocytic leukemia cell line

Ascorbate free radical stimulates the growth of human promyelocytic leukemia cells (HL-60) in the presence of a limited amount of serum (1%) when added to the cells under conditions where it is impermeable. Maximum growth stimulation occurs at concentrations from 5 x 10(-9) to 2 x 10(-8) M. Ascorbate mimicks the stimulation effect of its free radical but stimulates at higher concentrations. Autoxidation of ascorbate by oxygen produces its free radical, which apparently causes growth stimulation. Ascorbate could be regenerated by intact cells in vitro, since prevention of autoxidation of ascorbate in the presence of cells is observed. Neither dehydroascorbate nor isoascorbate increases HL-60 cell growth. Short term incubation of cells in the presence of ascorbate free radical induced intracellular NADH oxidation. We propose that the stimulation of growth of HL-60 cells shown here could be caused by activation of the transplasma membrane electron transport system by the ascorbate free radical.

Polarization of plasma membrane glycoconjugates in amphibian epidermis during metamorphosis

Wheat germ agglutinin (WGA) binding sites have been examined in tadpole epidermal cells at the level of both light and electron microscopy using the WGA-ovomucoid-gold technique. In premetamorphic tadpoles the reaction was observed on the plasma membranes of epithelial cells showing a gradient from inner to outer membranes. These glycoconjugates were polarized during development, and at the end of metamorphic climax they were only located in plasma membranes of stratum corneum. The existence of an apical cell surface coat is needed to facilitate the absorption of water through the adult epidermis. The possible implications of this polarization process are discussed.

Cell surface glycoconjugates control the activity of the NADH-ascorbate free radical reductase of rat liver plasma membrane

Plasma membrane isolated by two-phase partition from rat liver showed rates of ascorbate free radical reduction by NADH of 4-5 nmoles of oxidized NADH/min/mg protein. This activity was inhibited 80% by ConA and up to 97% by WGA and LFA lectins. NADH-ascorbate free radical reductase was also inhibited in rat liver plasma membranes preincubated with neuraminidase or trypsin, but no additional inhibition was observed in the presence of LFA after enzyme digestion. It appears that the integrity of glucan moieities of the cell surface glycoconjugates are necessary for the optimal function of this activity that could be considered as part of the transplasma membrane electron transport system.

Lectin binding patterns in amphibian epidermis

A battery of 6 different horseradish peroxidase conjugated lectins has been employed for structural localization of glycoconjugates in amphibian epidermis. Lens culinaris (LCA) lectin stained the basal membrane and gave no significant reaction on the epidermal layers. Canavlia ensiformis (Con A) and Griffonia simplicifolia II (GS II) lectins bound the keratinocyte cytoplasm and the basal membrane as well. Ulex europaeus I (UEA I) lectin had only reactivity with flask cells. Griffonia simplifolia I (GS I) and Glycine max (SBA) lectins preferentially bound the cell membranes of keratinocytes, being the intensity of the staining gradually increasing from the stratum spinosum to the stratum granulosum. These results show that UEA I, GS I, and SBA are good markers to distinguish different cell types and the degree of keratinocytes differentiation.