The effect of combining antitubulin agents on differentiated and undifferentiated human colon cancer cells.

The cytotoxicity of sequential combinations of a taxoid [paclitaxel (TAX) or docetaxel (TXT)] with a vinca alkaloid [vinorelbine (NVB)] was compared in differentiated and undifferentiated HT29-D4 cells. Agents were titrated from low doses inducing no modification of microtubule network to high doses corresponding to the clinically relevant concentrations that block mitosis. For undifferentiated cells, the sequential combination NVB/TAX was more efficient than TAX/NVB (22% cell survival versus 37% for 5 nM TAX and NVB). Surprisingly, we successively obtained synergism for low doses of both compounds [NVB (1-5 nM) and TAX (1-15 nM)], then additivity and finally antagonism when one of the compounds was at the concentration inducing mitotic block. The three patterns of results were also obtained with NVB/TXT combinations. For the synergistic combinations at the lowest concentrations, cytotoxicity occurred by apoptosis following mitosis. For differentiated cells, the most cytotoxic combinations were 1 microM TAX or TXT for 3 days followed by 1 microM NVB for 3 days, and 0.75 nM TAX or TXT for 9 days followed by 1 microM NVB for 3 days, the latter producing synergistic effects. Cytotoxicity occurred by apoptosis for the two states of differentiation. Major differences depending on cell phenotype were demonstrated: low sensitivity of differentiated cells to antitubulin agents and the difference in apoptotic pathways since mitosis is not involved in differentiated cells.

Reflex relationships between the cervical esophagus and the respiratory system in cats.

The present study focused on reflex relationships between the esophagus and the respiratory system in cats, namely the changes in airway tone and pulmonary circulation elicited by mechanical or acid (pH 2) stimulation of esophageal afferents. One-minute of sustained distension of the cervical esophagus increased tracheal pressure (PTr), decreased pulmonary artery pressure (PPA) and to a higher extent pulmonary blood flow (QPA) and lowered arterial blood pressure (Pa). This was associated with significant variations in arterial blood gases (increased PaO2 and decreased PaCO2). Acid stimulation of the cervical esophagus caused a marked increase in PTr and a modest fall in QPA. In both circumstances, cervical bivagotomy abolished PTr changes, whereas the changes in pulmonary hemodynamics but not in Pa were then accentuated. Further cervical sympathectomy suppressed the vascular response. These observations show the existence of reflex influences of esophageal afferents on the control of airway tone and pulmonary vascular resistance. The vagus nerve is the efferent arm of the bronchomotor reflex whereas modulation of the sympathetic control of pulmonary circulation seems to be responsible for the changes in pulmonary hemodynamics.

Assessment of an airway-to-pulmonary circulation reflex in cats.

In anesthetized, mechanically ventilated cats we studied the effects on pulmonary circulation of sustained distension or increased air flow stream in an isolated, innervated upper airway segment constituted by the cervical trachea, the larynx and the pharynx. Direct and averaged pulmonary artery pressures and blood flows were measured. In intact cats, sustained distension as well as increased air flow stream in the upper airway segment induced significant, marked increase in pulmonary artery pressure with concomitant decrease in blood flow. No change in heart rate occurred. Section of the superior laryngeal nerves (SLNs), which denervated the tracheolaryngeal segment but not the epipharynx, markedly reduced and delayed the pulmonary vascular response to mechanical stimulation of the upper airways. The response was not found after cervical bivagotomy. The present observations demonstrate the existence of an airway-to-pulmonary circulation reflex, largely mediated through SLNs afferent pathways, the vagus nerve constituting the efferent arm of the reflex.

Effect of temperature on the contractile response of isolated rat small intestine to acetylcholine and KCl: calcium dependence.

The influence of temperature on phasic and tonic components of isometric tension of the isolated rat small intestine was investigated at two temperatures (15 degrees C and 21 degrees C) where spontaneous movements were not evident. Warming did not shift acetylcholine-response curve whereas it enhanced the amplitude of maximal tension. The rate of tension development varied with acetylcholine concentration and increased with temperature. Warming enhanced and accelerated responses to single doses of high KCl. The effect of temperature on acetylcholine responses was mimicked by lowering calcium concentration in the bathing medium but in zero-calcium medium responses were higher at 21 degrees C than at 33 degrees C. Discussion of previous reports underlines that opposite observations on the effect of temperature on smooth muscle contraction are mainly explained by experimental protocols. In turn, it is suggested that the obtained effects of temperature might be related to the regulation of intracellular calcium concentration.

The isochore patterns of mammalian genomes and their phylogenetic implications.

The compositional distributions of high molecular weight DNA fragments from 20 species belonging to 9 out of the 17 eutherian orders were investigated by analytical CsCl density gradient centrifugation and by preparative fractionation in Cs2SO4/BAMD density gradients followed by analysis of the fractions in CsCl. These compositional distributions reflect those of the isochores making up the corresponding genomes. A "general distribution" was found in species belonging to eight mammalian orders. A "myomorph distribution" was found in Myomorpha, but not in the other rodent infraorders Sciuromorpha and Histricomorpha, which share the general distribution. Two other distributions were found in a megachiropteran (but not in microchiropteran, which, again, shares the general distribution) and in pangolin (a species from the only genus of the order Pholidota), respectively. The main difference between the general distribution and all other distributions is that the former contains sizable amounts (6-10%) of GC-rich isochores (detected as DNA fragments equal to, or higher than, 1.710 g/cm3 in modal buoyant density), which are scarce, or absent, in the other distributions. This difference is remarkable because gene concentrations in mammalian genomes are paralleled by GC levels, the highest gene concentrations being present in the GC-richest isochores. The compositional distributions of mammalian genomes reported here shed light on mammalian phylogeny. Indeed, all orders investigated, with the exception of Pholidota, seem to share a common ancestor. The compositional patterns of the megachiropteran and of Myomorpha may be derived from the general pattern or have independent origins.

[Use of codons in plant lectins]. / Usage des codons chez les lectines végétales.

Codon usage in the coding region of mature lectins has been examined for 11 plant species (8 leguminoseae, 1 euphorbiaceae, 2 gramineae). The different legume lectins exhibit nearly the same codon usage pattern whereas the choice for the silent position of codons is non-random.

Stimulation of 2',3'-cyclic nucleotide 3'-phosphodiesterase in human lymphocytes by Robinia pseudoacacia lectin.

2',3'-Cyclic nucleotide 3'-phosphodiesterase (CNP) activity was studied in human peripheral blood lymphocytes. Incubation of human lymphocytes with optimum mitogenic concentrations of Robinia pseudoacacia lectin produced an increase in CNP activity. This increase was not detected before 24 h of incubation. Furthermore, whereas unfractionated lymphocytes exhibited activation of CNP, this was not observed in B and T cell subpopulations.

Fluorescence anisotropy decay of ethidium bound to chromatin.

The fluorescence anisotropy decays of the chromatin ethidium complexes have been measured in solutions in which the dye was bound to the high affinity sites of the nucleosome DNA. Energy transfers between chromatin-bound ethidium molecules cause an increase of naked DNA-ethidium complexes. This result implies that the high affinity sites are clustered on a short nucleosomal DNA segment. Quantitative analysis of the experimental data by computer simulations of the energy transfer process, shows that these sites are gathered on a single nucleosomal DNA segment, 28 base pairs long. Such a segment probably belongs to the nucleosomal "linker", contributing about half of it.

Location of the ethidium binding sites of high affinity in chromatin.

The influence of H1 and H5 histones proteins upon the accessibility of ethidium bromide into chromatin is studied by steady-state fluorescence anisotropy in the range of r-values ([Dye]/[Phosphate]) smaller than 0.01. This corresponds to the very strong binding process. When H1 and H5 are present, the DNA segment which contains the binding sites is 25-30 base pairs long, even if H1 and H5 are digested by trypsin or by natural proteolysis, but presumably still interacting with the DNA chromatin. On the contrary, when H1 or H5 are separated from chromatin by an increase of the ionic strength, ethidium binds to a segment of DNA about 55-60 base pairs long. We may explain the results by assuming that the ethidium sites are located on a continuous segment constituting about one half of the linker, the other half interacting with H1 and H5. When chromatin is depleted from these proteins, the high affinity sites are distributed all along the linker.

The specificity of a neutral deoxyribonuclease from Cancer pagurus.

The recently isolated neutral deoxyribonuclease from crab (Cancer pagurus) testes has been characterized in its mode of action and its specificity. The enzyme is a typical endonuclease, forming 5'-phosphate oligonucleotides of large average size; after extensive digestion of calf thymus DNA over 75% of the fragments have a size larger than pentanucleotides and mononucleotides are absent. As far as specificity is concerned, thymidine is very abundant in the 5'-penultimate position (approximately 50%) and in the 3'-terminal position (37%) and almost absent in the 5'-terminal position (approximately 1%), the values quoted concerning Escherichia coli digests of average size (Pn) between 50 and 10.