Specific Binding of [3H]Pyrilamine to Histamine H1 Receptors in Guinea Pig Brain In Vivo: Determination of Binding Parameters by a Kinetic Four-Compartment Model

The binding of [3H]pyrilamine, a selective ligand of histamine H1 receptors, to guinea pig brain in vivo was compared with its binding to a brain homogenate. The pharmacological properties (regional distribution, saturability, and stereoselectivity) of the [3H]pyrilamine binding in vivo were similar to those of the in vitro binding to brain homogenate. A dynamic four-compartment model was proposed for the analysis of the kinetics of [3H]pyrilamine binding in vivo. The receptor constants in vivo were determined by a computer-fitting method after correcting the radioactivity of arterial plasma and brain for the presence of radioactive metabolites. The in vivo association and dissociation were 213 and 42 times, respectively, slower than those of in vitro binding at 37 degrees C. A possible mechanism for slow association and dissociation in vivo is discussed.     

Hepatocyte cell lines established from transgenic mice harboring temperature-sensitive simian virus 40 large T-antigen gene.

To establish cell lines exhibiting differentiation phenotypes, the immortalized cell lines were rapidly established from the primary culture of different tissues of transgenic mice harboring SV40 temperature-sensitive large T-antigen gene. The established cell lines grew at permissive temperature (33 degrees C), but not at nonpermissive temperature (39 degrees C). Several different cell types could be rapidly immortalized and cloned from the adult transgenic mice tissues. Among those cell lines, the established hepatocyte cell lines (TLR cell lines) exhibited liver-specific morphological and biochemical properties, but their properties were not coupled with the growth condition modified by temperature. The hepatocyte cell lines showed an inducibility of P450IA1 by 3-methylcholanthrene as observed in rat livers and this liver-specific function was stable even after 6 months of culture by continuous passages.     

Effects of inorganic nitrogen application on the dynamics of the soil solution composition in the root zone of maize

The effect of inorganic nitrogen (N) fertilizer on the ionic composition of the soil solution under maize (Zea mays L.) was studied. A pot experiment was carried out with two treatments combined factorially, with or without N application (Ca(NO₃)₂; +N and –N treatments, respectively), and with or without plants. Three looped hollow fiber samplers were installed in each pot to sample soil solutions nondestructively from the root zone, seven times during the 50-day growth period. Plants were harvested on the 50th day, and their nutrient contents determined.Effects of N fertilizer on the soil solutions were observed by the first sampling, 2 days after sowing. The concentrations of Ca and NO₃ ^– and electrical conductivity (EC) increased significantly in the +N treatments as direct effects of fertilizer application. In addition, the concentrations of Mg, K, Na and H⁺ also increased and that of P decreased significantly as indirect effects caused by the re-establishment of chemical equilibria. This suggested the greater supply as well as the greater possibility of leaching loss not only of NO₃ ^– but also of Ca, Mg and K. In the treatments with plants, the concentrations of NO₃ ^–, Ca, Mg and K decreased with time and pH increased significantly compared with the unplanted soil. The depletion of N in the soil solution roughly agreed with the amount of N taken up by the plant. The depletions of K from the soil solution amounted to less than 10% of the amount of the K taken up, suggesting intensive replenishment of K from exchange sites in the soil. Depletions of Ca and Mg were several times higher than the amounts taken up, indicating that the depletions resulted from the adsorption of the divalent cations by the soil rather than uptake by plants. Because NO₃ ^– is hardly absorbed by exchange sites in soil and was the dominant anion in solution, it was concluded that NO₃ ^– had a major role in controlling cation concentrations in the soil solution and, consequently, on their availability for uptake by plants as well as their possible leaching loss. ei]H Marschner     

Molecular interactions between micellar polysialogangliosides and affinity-purified tetanotoxins in aqueous solution

Two-affinity purified tetanotoxin forms, TeToA and TeToB, with different affinities for gangliosides were characterized by analytical ultracentrifuge, circular dichroism (CD), and amino acid composition. Both toxin forms share a common sedimentation coefficient of about 6-7 S and similar alpha-helicity values, but they vary in amino acid composition. Incubation of TeToB with micellar polysialogangliosides results in formation of high (21-24 S) and medium (13-15 S) size toxin-micellar ganglioside aggregates as revealed by analytical ultracentrifuge technique. At TeToB/[N-acetylneuraminyl]-galactosyl-N-acetylgalactosaminyl- [N-acetylneuraminyl-N-acetylneuraminyl]-galactosylglucosylceramide (GT1b) molar ratios of greater than 26, high molecular weight aggregates (Mr greater than or equal to 700,000) which contain between 3 and 5 toxin monomers are formed, whereas at molar ratios less than 15, about 1-2 monomers are present. TeToA does not form aggregates in the presence of gangliosides. A marked increase in the alpha-helix from about 20 to 39% is apparent in the CD spectrum of TeToB after interaction with ganglioside mixture (G1b). Cerebrosides, sulfatides, sphingomyelin, and phosphatidylserine also increase the alpha-helix, presumably because of an overall effect of lipids on the protein. TeToA and fragment B but not C also undergo similar changes in the presence of G1b, suggesting that the effect of ganglioside is not specific. The polarity of the CD spectra of a number of gangliosides is shifted from a negative to a positive value after interaction with tetanotoxin. The data are consistent with the interpretation of a discrete hydrophobic domain on the toxin heavy chain which interacts with micellar gangliosides to form macromolecular complexes.