No abstract

Interferon enhances alpha-bungarotoxin binding on 5-day-old rat myotubes. The increase is time- and dose-dependent. KD for alpha-bungarotoxin remains unchanged in the presence and in the absence of interferon, while the maximum number of binding sites is dramatically affected by interferon. Cycloheximide inhibits the effect of interferon, which suggests that the enhancement of alpha-bungarotoxin binding depends on protein synthesis.

We investigated the effect of rat interferon-alpha/beta (IFN) on the expression of glycerol phosphate dehydrogenase (E.C.1.1.1.8; GPDH), in both C6 cells and pure cultures of oligodendrocytes. IFNs are naturally produced inhibitors of cell growth that can also affect differentiated cell functions. GPDH is a biochemical marker for oligodendrocytes and is known to be developmentally regulated and steroid inducible. GPDH activity is induced by hydrocortisone (HC) 3.5 fold in C6 cells and 5 fold in oligodendrocytes compared to untreated cultures. A pretreatment of these cells with 75 U/ml of rat IFN-alpha/beta resulted in an inhibition of the HC induction of GPDH enzymatic activity by 50% and 40% in C6 cells and oligodendrocytes respectively. We also found that IFN impaired the accumulation of GPDH mRNA in both cell types. These results demonstrate that IFNs are capable of modifying the cellular response to hormones in cells of neuroepithelial origin, and suggest the possibility that IFNs may be able to influence the development and function of the brain.

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Fluorescence anisotropy measurements to determine membrane fluidity have been generally performed with diphenylhexatriene (DPH) on purified membrane samples. This probe could not be used satisfactorily with intact cells, because it did not present any specificity for a particular type of membrane and labelled all the hydrophobic regions of the cell. We have recently focussed our attention on the cationic derivative of DPH, trimethylamino-diphenylhexatriene (TMA-DPH). This molecule displays excellent photophysical properties in hydrophobic media: lifetime 6 ns (DPH 8 ns), quantum yield 0.55 (DPH 0.75), and is not fluorescent in water. 1,2 In comparison with DPH and the other fluorescent probes previously used in membrane fluidity determinations it was given evidence 3 ,4 by fluorescence micrography and by fluorescence intensity measurements, to have two particularly favorable features : (i) it is incorporated in membranes very rapidly (ii) when it is interacted with intact cells, it is retained specifically in the plasma membranes for periods of typically 30 min. before being internalized.These properties made TMA-DPH a relevant fluorescent probe for fluidity measurements of the plasma membranes of intact cells. As such it has been used satisfactorily in monitoring fluidity changes in : mast cells upon histamine release,s erythrocytes upon parasitemia by plasmodium,6 purified mitochondria upon treatment by succinate. 7 On the other hand, the evidence of a partition equilibrium of TMA-DPH between membranes and water 4 suggested an original method to monitor exocytosis phenomena by simple fluorescence intensity measurements. 8 LIMITATIONS TO ITS USE Internalization featuresThe kinetics of the internalization of TMA-DPH after its stay in the cell plasma membranes depend actually on the cell type. In fibroblasts, lymphocytes and mast cells the process started after 30 min. at 37°C.