Biphasic nature of the binding of cationic amphipaths with artificial and biological membranes

We have studied the interaction with liposomes and red cell membrane of various cationic amphipaths, chlorpromazine, methochlorpromazine, imipramine and propranolol. At low concentrations the interaction is a partition of the molecule between the lipid hydrophobic phase and the aqueous medium. The extent of the partition is dependent on the membrane composition or physical properties, on the incubation conditions (pH, ions) and on the amphipath used. After a given amount of amphipath has entered in the membrane, a new type of interaction appears which leads to an apparent saturable association. This association, which probably involves the anionic groups of the membrane components, might result from structural or/and electrical membrane perturbations induced by the presence of drug molecules between the phospholipids. Thus the interaction of a molecule of cationic amphipath with a membrane varies according to the amount of drug present.     

Effects of harmaline on ion transport and oxygen consumption by the bovine tracheal epithelium

The alkaloid harmaline is known to affect various membrane transport systems. This study examines the action of the drug on the short-circuit current (I0) and on the oxidative metabolism (Jr) in the tracheal epithelium of the cow. In this tissue I0 corresponds to the sum of two active transports: Na+ is absorbed and Cl- is secreted by a process based on the activity of the Na+ pump. A well defined relationship has been previously demonstrated between these active transports and the rate of O2 consumption (Schoenenweid et al., 1984 b). Low concentrations of harmaline (10(-6) to 5.10(-6) M) induced a small stimulation of I0. In contrast, larger concentrations (between 5.10(-5) and 10(-3) M) yielded a dose-related inhibition of I0, with an apparent concentration yielding 50% of maximal effect of 7.1.10(-4) M and maximal effect approaching 100%. The action was fully reversible after removal of the drug. The measurements of the fluxes of 22Na and 36Cl revealed that harmaline at a concentration of 8.10(-4) M, which decreased the I0 by 74 +/- 1% (n = 23), diminished both Na+ and Cl- transports, by 81 and 52%, respectively. The time course of I0 decay following the administration of harmaline was made of three components, with half-times of 0.34, 2.2 and 15.2 min. The time course was not appreciably modified when Cl- secretion was abolished with furosemide. Although harmaline, 10(-3)M, inhibited markedly I0, it did not modify Jr significantly. In contrast, when K+ in the incubation solution was omitted, both Ji and Jr were lowered.(ABSTRACT TRUNCATED AT 250 WORDS)     

Kinetic evidence of a surface membraneous step during the endocytosic process of 3H-labelled asialoorosomucoid and its alteration in diabetic mellitus rats

The apparent internalization rate constant of asialoorosomucoid in normal and diabetic hepatocytes was determined using different experimental processes, either following a synchronous wave of prebound ligand or a continuous flux ligand endocytosis, either alone or simultaneously. In continuous flux conditions, no difference between normal and diabetic hepatocytes appeared (k = 0.15 +/- 0.04 and 0.11 +/- 0.02 min-1, respectively). In contrast, in the one-turn endocytosis of prebound ligand, k was lower for diabetic hepatocytes than for normal ones whether it was measured alone (0.20 +/- 0.03 and 0.59 +/- 0.09 min-1, respectively) or simultaneously with a continuous flux of unlabelled ligand (0.25 +/- 0.03 and 0.70 +/- 0.08 min-1, respectively). These differences are attributed to an impediment or a delay in the preclustering of receptors in coated pits at the cell surface of diabetic cells.     

Hybridization of DNA from methanogenic bacteria with nitrogenase structural genes (nifHDK)

Summary Using the Southern hybridization technique, homologies were examined between restricted DNA of four methanogenic bacteria (Methanobacterium ivanovi, Methanobacterium thermoautotrophicum, Methanococcus voltae, Methanosarcina barkeri) and the nif (nitrogen fixation) genes of Klebsiella pneumoniae and Anabaena strain 7120. With K. pneumoniae probes, no hybridization was observed with nifA, nifNE, and nifJ but positive results were obtained with the nifHDK genes coding for nitrogenase. Homology was detected, in the four strains, with K. pneumoniae and Anabaena nifH probes. In M. voltae and M. ivanovi, the homology found with nifH was estimated to be about 70% and a weaker hybridization was observed also with nifD and nifK. In M. voltae, the sequence homologous to nifH was found on a 3.0 kbp HindIII fragment and sequences homologous to nifD and nifK on a 3.8 kbp HindIII fragment. The 3.0 kbp fragment was cloned and the region homologous to nifH was localized more precisely. When this fragment was used as a probe against other DNAs, it behaved as a K. pneumoniae and Anabaena nifH probe. The results suggest that the structural genes for nitrogenase may be present in archaebacteria and raise interesting questions regarding their evolution.     

Alterations in the Fatty Acid Composition of Rat Brain Cells (Neurons, Astrocytes, and Oligodendrocytes) and of Subcellular Fractions (Myelin and Synaptosomes) Induced by a Diet Devoid of n-3 Fatty Acids

Abstract: Rats were fed through four generations with a semisynthetic diet containing 1.0% sunflower oil (6.7 mg/ g n-6 fatty acids, 0.04 mg/g n-3 fatty acids). Ten days before mating, half of the animals received a diet in which sunflower was replaced by soya oil (6.6 mg/g n-6 fatty acids, 0.8 mg/g n-3 fatty acids) and analyses were performed on their pups. Fatty acid analysis in isolated cellular and subcellular material from sunflower-fed animals showed that the total amount of unsaturated fatty acids was not reduced in any cellular or subcellular fraction (except in 60-day-old rat neurons). All material from animals fed with sunflower oil showed an important reduction in the docosahexaenoic acid content, compensated (except in 60-day-old rat neurons) by an increase in the n-6 fatty acids (mainly C22:5 n-6). When comparing 60-day-old animals fed with soya oil or sunflower oil, the n-3/n-6 fatty acid ratio was reduced 16-fold in oligodendrocytes, 12-fold in myelin, twofold in neurons, sixfold in synaptosomes, and threefold in astrocytes. No trienes were detected. Saturated and monounsaturated fatty acids were hardly affected. This study provides data on the fatty acid composition of isolated brain cells.     

Diabetes-induced variation in hepatic binding protein

The total capacity of hepatocytes to bind asialoorosomucoid was measured on normal and streptozotocin diabetic rats. 4 days after the streptozotocin injection, a slight decrease of total receptor concentration was observed while a more marked reduction of cell surface receptor occurred. In animals sacrificed 11 days after the streptozotocin injection, the total capacity of hepatocytes to bind asialoorosomucoid was about 70% of the normal level.     

Structural Aspects of Saltatory Particle Movement

A variety of cells possess particles which show movements statistically different from Brownian movements. They are characterized by discontinuous jumps of 2–30 µ at velocities of 0.5–5 µ/sec or more. A detailed analysis of these saltatory, jumplike movements makes it most likely that they are caused by transmission of force to the particles by a fiber system in the cell outside of the particle itself. Work with isolated droplets of cytoplasm from algae demonstrates a set of fibers involved in both cytoplasmic streaming and saltatory motion, suggesting that both phenomena are related to the same force-generating set of fibers. Analysis of a variety of systems in which streaming and/or saltatory movement occurs reveals two types of fiber systems spatially correlated with the movement, microtubules and 50 A microfilaments. The fibers in Nitella (alga) are of the microfilament type. In other systems (melanocyte processes, mitotic apparatus, nerve axons) microtubules occur. A suggestion is made, based on work on cilia, that a microtubule-microfilament complex may be present in those cases in which only microtubules appear to be present, with the microfilament closely associated with or buried in the microtubule wall. If so, then microfilaments, structurally similar to smooth muscle filaments, may be a force-generating element in a very wide variety of saltatory and streaming phenomena.