Characteristics of ouabain binding to isolated trout hepatocytes

Summary Na⁺, K⁺ exchanges were studied in isolated hepatocytes of the rainbow trout, Salmo gairdneri. Ouabain at 10^–4 M produced maximal inhibition (95%) of K⁺ uptake and enhanced intracellular Na⁺ accumulation, showing that active fluxes account for a very large proportion of Na⁺ and K⁺ exchanges. Inhibition of the Na–K pump by ouabain was significant at low concentrations (10^–8 M). When external K⁺ concentration was reduced from 7 mM to 0.5 mM, half maximum inhibition (IC₅₀) of K⁺ uptake was obtained at a 22-fold lower concentration of ouabain confirming that ouabain and potassium compete at the same pump site. Time-course analysis of [³H]ouabain binding indicated a two-component kinetics: one component saturable and dependent on K⁺ concentration in the medium, the other linear and independent of external K⁺. The ouabain binding site number, determined by Scatchard plots, remained constant (ca. 2.5·10⁵ per cell) and independent of the external K⁺ concentration (7, 0.5 or 0 mM), while the dissociation constant (K_D) decreased from 4.2 M to 7.3 nM when K⁺ was removed from the Hank's medium. These ouabain binding sites are characterized by an exceptionally low turnover rate (400 min^–1), as estimated from ouabain-sensitive K⁺ flux, in comparison to those described in other cell types of higher vertebrates. At each external K⁺ concentration studied, the inhibition of K⁺ uptake and ouabain binding measured as a function of ouabain concentration indicated a strict correlation between the degree of K pump inhibition and the amount of bound glycoside.     

Vibratory communication in spiders

We analyzed the response of the vibration sensitive lyriform organ on the metatarsus of female spiders (Cupiennius salei) to dummies of male courtship vibrations. One of the two representative slits studied is sharply tuned to 500 Hz. Only the other slit is sensitive enough at lower frequencies to represent the parameters contained in the behaviourally effective dummies:

1. Amplitude. The physiological threshold is similar to the behavioural threshold. The stimulus acceleration amplitudes leading to a good synchronization between response and temporal stimulus pattern coincide with those effectively eliciting a behavioural response. The most frequent spike intervals remain nearly constant in this range. At acceleration amplitudes above the natural range, syllable and pause durations are misrepresented by the receptor response.
2. Frequency. Varying the carrier frequency between 35–500 Hz changes the most frequent spike intervals. Interval histograms resulting from behaviourally effective stimuli (50–200 Hz), however, are similr for carrier frequencies differing by a factor of 2.
3. Temporal pattern. Response duration reflects the temporal parameters of the stimulus. The most frequent spike interval only changes with temporal stimulus characteristics far off the natural range. The number of spikes during a syllable decreases in ongoing stimulus series. The quality of copying the temporal stimulus pattern remains unchanged, however.

     

Map of plasmid RP4 derived by insertion of transposon C.

We have determined the location of 36 sites on plasmid RP4 into which transposon C (an 8.5 × 10⁶ molecular weight DNA sequence conferring trimethoprim and streptomycin resistance) had spontaneously inserted itself. These were located by sucrose gradient analysis of EcoRI-generated and then, separately, the HindIII-generated DNA fragments from each RP4-TnC² plasmid. RP4 has a single EcoRI-susceptible site and, suitably displaced from this, a HindIII-susceptible site, whereas TnC has, respectively, one and two sites for these two enzymes. Thus the sizes of the restriction fragments depend on the location and orientation of the inserted TnC.Some of the RP4-TnC clones had lost one of the RP4 characters: transferability (Tra), tetracycline (Tc) or kanamycin (Km) resistances, but no ampicillin (Ap) sensitive clones were detected. Insertions giving each of these phenotypic changes cluster together at positions on the circular RP4 map that presumably locate the genes responsible for the Tra⁺, Km^r and Tc^r phenotypes. The Tra^? plasmids were grouped into four classes on the basis of their conferred phage sensitivities and plasmid copy numbers. The gene giving Ap^r was located by its known proximity to a BamHI-susceptible site. All the plasmids analysed had TnC inserted with one particular orientation. TnC insertions giving no detectable phenotypic change were not randomly placed around RP4, but clustered into certain regions. Two large regions, one containing TnA, had no TnC insertions. Ligation experiments with restriction fragments from various RP4-TnC plasmids led to the conclusion that both these regions contain genes essential to the replication and maintenance of RP4. The location of the HindIII site of RP4 within the gene giving Km^r should prove valuable to the use of this plasmid as a cloning vehicle.     

Neuropeptides in spinal cord injury: Comparative experimental models

The possible role of endogenous opioids in the pathophysiology of spinal cord injury was evaluated utilizing a variety of experimental models and species. In the cat, we have shown that β-endorphin-like immunoreactivity was increased in plasma following traumatic spinal injury; such injury was associated with a decrease in spinal cord blood flow (SCBF) which was reversed by the opiate receptor antagonist naloxone. Naloxone treatment also significantly improved functional neurological recovery after severe injury. Thyrotropin-releasing hormone (TRH), possibly through its “anti-endorphin” actions, was even more effective than naloxone in improving functional recovery in the cat. In a rat model, utilizing a similar trauma method, TRH proved superior to naloxone in improving SCBF after injury. In addition, naloxone at high doses attenuated the hindlimb paralysis produced by temporary aortic occlusion in the rabbit. The high doses of naloxone required to improve neurological function after spinal injury suggest that naloxone's actions, if opiate receptor mediated, may be mediated by non-μ receptors. Dynorphin, an endogenous opioid with a high affinity for the κ receptor, produced hindlimb paralysis following intrathecal administration in rats. Taken together, these findings suggest that endogenous opioids, possibly acting at κ receptors in the spinal cord, may serve as pathophysiological factors in spinal cord injury.     

Levels of organization and repetition phenomena in seed plants

Each plant can be recognized by its general shape. Nevertheless, this physiognomy is the result of a very precise structure that expresses the existence of a strong organization. The architecture of a plant depends on the nature and relative arrangement of each of its parts; it is at any given time the result of an equilibrium between endogenous growth processes and the constraints exerted by the environment. Architectural studies have been carried out for some twenty years and have led to the definition of several concepts that provide a powerful tool for studying plant form. The results obtained in this field show that the architecture of a plant can be summarized by a small number of elementary structures: internode, growth unit, axis, architectural model,... In the course of ontogenesis, these structures are repeated and reveal several levels of organization that seem to be only different stages of a common process of growth and transformation.

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Résumé Toute espèce végétale peut être reconnue par sa forme générale. Toutefois, au-delà de cet aspect physionomique, la forme d'une plante repose sur une structure très précise qui traduit l'existence d'une grande organisation. L'architecture d'une plante dépend de la nature et de la position relative de ses différentes parties; elle est à tout instant, l'expression d'un èquilibre entre des processus endogénes de croissance et des contraintes extérieures exercées par le milieu. D'origine assez récente, les études en architecture végétale ont permis de dégager quelques concepts qui rendent compte du développement des végétaux. Les résultats obtenus dans ce domaine montrent que l'architecture d'une plante peut être résumée par un petit nombre de structures élémentaires: entre-noeud, unité de croissance, axe, modèle architectural,... Au cours du développement, ces structures élémentaires se répètent et dérivent les unes des autres traduisant l'existence de plusieurs niveaux d'organisation au sein de l'organisme végétal. L'analyse architecturale permet de révéler et de caractériser ces différents niveaux qui apparaissent alors comme les étapes d'un même processus dans une séquence précise et ordonnée d'événements.

     

Cellular Source and Mechanisms of High Transcriptome Complexity in the Mammalian Testis

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Toward a role of dendritic cells in the germinal center reaction: triggering of B cell proliferation and isotype switching

We have reported previously that in vitro generated dendritic cells (DC) can directly regulate B cell responses. Recently, germinal center DC (GCDC) were identified within B cell follicles. Due to their particular localization, we have tested in the present study whether GCDC could contribute to key events characteristic of the GC reaction. Our present results demonstrate that 1) ex vivo GCDC induce a dramatic GC B cell expansion upon CD40 and IL-2 activation and drive plasma cell differentiation, 2) this property is shared by GCDC and blood DC, but not by Langerhans cells, 3) IL-12 production by GCDC is critical in GC B cell expansion and differentiation, and 4) importantly, GCDC also induce IL-10-independent isotype switching toward IgG1. These observations support the novel concept that GCDC directly contribute to the germinal center reaction.