Stimulation of the synthesis and non-competitive inhibition of alkaline phosphatase by theophylline in normal hamster fibroblasts and absence of response in transformed fibroblasts]

Theophylline increases the synthesis of alkaline phosphatase in normal Hamster fibroblasts (activity X6 after 24 hours with theophylline 10-3 M). The enzymatic activity of these cells is inhibited by theophylline in vitro (80% inhibition in the presence of theophylline 10-3 M). The inhibition seems to be non competitive, since the apparent Km of the enzyme is not modified. This stimulator and inhibitor effect of theophylline is absent in Hamster fibroblasts transformed by SV 40 virus.     

Rapid freezing of biologic tissue. Measurement of temperature and rate of freezing by thin-layer thermocouple]

An apparatus for rapid freezing of biological tissues by contact with a copper block cooled by liquid helium has been devised to reduce the contamination of copper block surface. It prevents the precooling of the specimen while going through the layers of cold helium gas surrounding the copper block and reduces the quantity of helium necessary for freezing. It also enables one to obtain easily reproducible results from freezing by immersion in liquid coolants. Freezing rates are measured directly, related to the specimen thickness, by a thin film thermocouple; its low thermal inertia gives speed measurements of the order of 100,000 degrees C/s.     

Nuclear membrane and chromatin network

Résumé Il existen un certain rapport entre la chromatine et des petites invaginations de la membrane nucléaire. Nous estimons que la charge positive de la membrane et la charge négative des chromosomes peut être la cause inductrice.