Increased phospholipase a activity and formation of communicative contacts between Acanthamoeba castellanii cells

1. 1. Exogenous 1-palmitoyl-sn-glycero-3-phosphorylcholine becomes incorporated into the membrane of A. castellanii within 2 min of incubation. 2. 2. Homogenates of A. castellanii are shown to contain phospholipase A activity. 3. 3. The phospholipase A activity is dependent on the population density of the culture. 4. 4. An increased phospholipase A activity in older cultures of A. castellanii, due to an increased population density, induces aggregation of these cells in a way that communicative contacts are formed. 5. 5. At pH 5.5, the pH value at which the cells were grown, the phospholipase A activity is stimulated by cAMP; at pH 8.0 no stimulation occurs

Absence of cell communication for fluorescein and dansylated amino acids in an electronic coupled cell system

Quantitative evaluation of the diffusion process of sodium fluorescein and dansylated amino acids in the salivary gland of the larvae of Drosophila hydei reveals that the differences in specific permeability between the junctional and nonjunctional membranes, as found for small ions, do not apply to the fluorescent probes. There are no significant differences between the pemeability properties for the different dansylated amino acids tested, and the same properties are found for sodium fluorescein

Freeze-etching: Freezing velocity and crystal size at different locations in samples

Freezing velocity was studied experimentally as well as theoretically in relation to sample size and location within the sample. Crystal sizes in a freeze-etch replica displaying the complete fracture area of a sample were compared to the experimental and theoretical results concerning freezing velocities at different locations in such a sample. The freezing velocity was found to be higher in the center and near the surface than halfway between the center and the outer surface of the sample. Also, the crystals in the center and near the border appear to be small as compared to the crystals in the other fracture domain