Activation propetties of the inward-recifying potassium channel on mammalian heart cells

Summary The early phase of activation of the inward-rectifying potassium channel is studied on single cells from guinea-pig heart. The current is quasi-instantaneous when it is outward, but activates with time when it is inward. This relaxation is exponential and its time-constant decreases with hyperpolarization. TheI/V curve reflects a strong inward rectification and has a negative slope conductance on depolarization. Similar results were recorded in the absence of sodium, calcium, chloride ions and in isotonic potassium. Cesium slows down the phase of activation, and eventually appears to block the channels by suppression of the activation. Barium, conversely, does not affect the activation, but promotes an inactivation of this current, which blocks it. These results are independent on the cells' dissociation method. They suggest that this current is the inward rectifier, calledI _K1 on heart. Its activation curve suggests that the inward and outward currents are flowing through the same channels. The inward rectifier is time-and voltage-dependent on heart as on other tissues. The effects of cesium and barium are also similar. The importance of its negative slope conductance is discussed.     

Formation and regeneration of Frankia protoplasts

A technique for forming protoplasts from Frankia cells and regenerating them to the normal hyphal mode of growth is described. Electron microscopy proved that protoplasts were studied and not spores or small hyphae. Regenerated colonies were investigated for genetic markers. One ArI3 colony had been cured of its plasmids without being affected in its symbiotic properties.     

Limitation of access to highly palatable foods increases the norepinephrine content of many discrete hypothalamic and amygdaloidal nuclei of rat brain

The norepinephrine (NE) concentration of 14 discrete brain nuclei of rats fed with either purina rat chow or highly palatable foods, given $\text{ad litibum}$ or in a restricted quantity isocaloric with the Purina rat chow diet, was measured by high performance liquid chromatography with electrochemical detection. The NE level was significantly increased in the n. suprachiasmaticus, n. paraventricularis, n. arcuatus and n. amygdaloideus (medialis, corticalis, centralis, basalis pars lateralis, lateralis pars posterior) of rats fed with palatable foods given in restricted amount. The increased NE level seems to be associated with the limitation of access to highly palatable food whilst the regimen composition and the palatability of foods are not implicated in this phenomenon. Some hypothalamic and amygdaloid NE-containing neurones can be affected by food-restriction stress, suggesting a role of this neuronal system in feeding activity.     

Serum lipids and cholesterol distribution in lipoproteins of exercise-trained female rats fed sucrose

This study was undertaken to evaluate the combined effects of sucrose feeding and exercise training on serum insulin, triglycerides, as well as cholesterol and its distribution into lipoproteins of female Wistar rats. The animals were fed ad libitum either laboratory chow alone, or chow and a 32% aqueous sucrose solution. Half of each dietary group was submitted to an exercise-training program. Both sucrose feeding and exercise training elicited greater energy intake. Sucrose feeding produced a marked elevation in triglyceridemia that was prevented by exercise training. Insulin levels paralleled those of triglycerides. The sucrose-fed animals had higher total cholesterol levels than the animals given chow. Although exercise training did not affect total cholesterol in the chow-fed animals, it partly prevented the sucrose-induced elevation in total cholesterol. Cholesterol in the lipoproteins of lower densities was increased significantly with sucrose feeding, and exercise training totally prevented this augmentation. The amount of cholesterol carried by high-density lipoprotein (HDL) was not affected by exercise training in the chow-fed animals. In contrast, sucrose feeding increased HDL-cholesterol in sedentary animals, whereas exercise training partly prevented this increase. The HDL/total cholesterol ratio was similar in all groups. Changes in insulin concentration underline the importance of this hormone in the regulation of blood lipid levels.     

Presence of an essential arginyl residue in D-β-hydroxybutyrate dehydrogenase from mitochondrial inner membrane

D-β-hydroxybutyrate dehydrogenase, a lipid requiring enzyme, is rapidly and completely inactivated by phenylglyoxal, 2,3-butanedione and 1,2-cyclohexanedione. Inactivation, which occurs at the millimolar range, depends on the nature of buffer, borate ions are required to get enzyme inactivation by 2,3-butanedione. Most of the inactivation follows a pseudo first order kinetics, the stoichiometry being of one to one. Presence of NAD⁺ or methylmalonate (a substrate-like compound) prior addition of inhibitor does not affect inactivation, while methylmalonate in presence of NAD⁺ strongly protects against inactivation. Chemical modification of the enzyme does not affect K_D of NAD while K_M of β-hydroxybutyrate and Ki of methylmalonate (protecting agent) increase. In view of the high specificity of these inhibitors for arginyl residues of proteins, these results are in favour of the presence of at least one arginyl residue essential for enzyme activity and located in, or near the substrate binding site.     

New discoveries of pliocene hominids and artifacts in Hadar: International Afar Research Expedition to Ethiopia (fourth and fifth field seasons, 1975–1977)

This note enumerates the paleontological discoveries of the Afar Expedition in 1975–1977.     

Effect of nicotine on in vivo secretion of melanocorticotropic hormones in the rat

Corticosterone, ACTH, β-endorphin and α-MSH were measured in rat plasma by radioimmunoassay before and 2,5,15,30 minutes after an intraperitoneal injection of nicotine (500 μg/Kg b.w.). Nicotine induced an increase of plasma corticosterone (p < 0.05 at t + 15 min), ACTH and β-endorphin (p < 0.01 at t + 5 min) and a decrease of α-MSH (p < 0.005 at t + 15 min). Dose response experiments showed an increase of corticosterone, ACTH, β-endorphin 15 min after 250 μg/Kg b.w. nicotine I.P., no effect being observed after injection of 100 μg/Kg b.w. The decrease of α-MSH was observed 15 min after 100, 250 or 500 μg/Kg b.w. nicotine I.P. Our results suggest that the increase of corticosterone is mediated through ACTH release.     

Structure granaire,réduction du NADP et photophosphorylation des chloroplastes isolés de feuilles d'orge

Summary Barley chloroplasts (Hordeum vulgare L.) have been isolated in aqueous medium by previously described techniques which preserve the outer plastid membrane in numerous chloroplasts. Thus intact chloroplasts are concentrated in Class I fraction and non intact in Class II fraction. A third type, broken Class I, is obtained by the action of a very dilute buffer solution.The observation of freeze-etched preparations has shown that the main distinctive character between the two classes is not so much the presence or the absence of the outer plastid membrane, as it was assumed, as the state of the thylakoids. In Class I chloroplasts grana are shrunken, in those of Class II, grana are swollen. In both cases the outer membrane may or may not be preserved.The breakage of chloroplasts resulting from treatment with osmotic shocks is due to the dilatation of the extra-lamellar matrix. The swelling of intra-thylakoidal volumes resulting from such a treatment is much less important.It is shown that Class I chloroplasts have a very low NADP reductase activity which is strongly increased after the chloroplasts are broken by osmotic shocks. Such a treatment is without any effect on Class II chloroplasts, which always exhibit a low NADP reductase activity.The situation is rather different in regard to photophosphorylation. It is also lower in Class II than in Class I, but after breakage by osmotic shocks the increase of this activity is weak, and much less significant than the increase observed in NADP reduction. The compression and cohesion of the thylakoids is not required for high photophosphorylation activity with artificial electron acceptors such as PMS. In this case cyclic photophosphorylation is higher in Class II than in Class I.

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Abbreviations ADP, ATP adénosine di et triphosphate - EDTA éthylène diamine trétaacétate - NAD, NADP, NADPH₂ nicotinamide adénine dinucléotide, d° phosphate (formes oxydée et réduite) - PMS phénazine méthosulfate - Pi phosphate inorganique     

Genes encoding the small subunit of RUBISCO belong to two highly conserved subfamilies in Nicotianeae

Summary The sequences of seven complementary DNAs or genes encoding the small subunit (SSU) of ribulose-1,5-bisphosphate carboxylase oxygenase (RUBISCO) in several Nicotianeae were examined. Two new SSU genes isolated fromNicotiana sylvestris were included. Both sequence comparisons and Southern analyses with specific probes reveal that SSU genes fall into two homogeneous subfamilies that are highly conserved in Nicotianeae and are also present in other Solanaceae. Additional criteria such as number of introns and level of expression fitted to this classification. Homogeneity must have been maintained by gene conversion and/or an unusually high fidelity of DNA replication, whereas traces of slippage-stranded DNA mispairing and/or transposition probably explain local changes. Taken as a whole, these results show that the divergence between the two subfamilies predated the divergence between genera inside the Solanaceae, but that Nicotianeae retained the most simple SSU gene family structure.