Evaluation of the annexins as potential mediators of membrane fusion in exocytosis

Membrane fusion is a central event in the process of exocytosis. It occurs between secretory vesicle membranes and the plasma membrane and also among secretory vesicle membranes themselves during compound exocytosis. In many cells the fusion event is regulated by calcium. Since the relevant membranes do not undergo fusion in vitro when highly purified, much attention has been paid to possible protein mediators of these calcium-dependent fusion events. The annexins comprise a group of calcium-dependent membrane-aggregating proteins, of which synexin is the prototype, which can initiate contacts between secretory vesicle membranes which will then fuse if the membranes are further perturbed by the addition of exogenous free fatty acids. This review discusses the secretory pathway and the evidence obtained fromin vitro studies that suggests the annexins may be mediators or regulators of membrane fusion in exocytosis.     

Fine structure of external ‘genital’ papillae in the fresh water miteHydrovolzia placophora (Hydrovolziidae,Actinedida, Actinotrichida,Acari)

Numerous genital papillae are described for the first time in the freshwater miteHydrovoliza placophora. In contrast to other actinotrichid mites, these organs are located on the epimeral plates, thus well removed from the genital opening. Ultrastructurally, the papillae correspond to those of other freshwater mites and are thus likely involved in ion/osmoregulation.     

Two-dimensional maps in very acidic immobilized pH gradients

Up to the present time it has been impossible to perform two-dimensional (2-D) separations in very acidic immobilized pH gradients (IPG), due to the lack of suitable buffering acrylamido derivatives to be incorporated into the polyacrylamide matrix. The advent of the pK 3.1 buffer (2-acrylamido glycolic acid; Righetti et al., J. Biochem. Biophys. Methods 16, 1988, 185–192) allowed the formulation of such acidic gradients. We report here separations in IPG pH 2.8–5.0 intervals of polypeptide chains from total lysates of rat intestinal and liver cells and 30S and 50S ribosomal proteins from Halobacterium marismortui. Conditions are given for highly reproducible first and second dimensions gels and for a proper silver staining of 2-D maps with practically no background deposition.     

Nicotine Effects on Dopamine Clearance in Rat Nucleus Accumbens

Abstract: In vivo voltammetry was used to measure the clearance of exogenously applied dopamine (DA) in the nucleus accumbens following acute systemic nicotine administration in urethane-anesthetized rats. The IVEC-5 system was used for continuous in vivo electrochemical measurements. A finite amount of DA was pressure-ejected (25–100 nl, 200 µ M barrel concentration) at 5-min intervals from micropipettes (tip diameter, 10–15 µm) positioned 250 ± 50 µm from the recording electrode. The peak DA concentration after each DA ejection was significantly decreased in rats following nicotine, but not in rats given saline. In addition, when mecamylamine was administered 20 min before nicotine it clearly antagonized nicotine effects. These results suggest that nicotine may actually facilitate DA transporter systems within the nucleus accumbens.     

Influence of BA and sucrose on the competence and determination of pepper (Capsicum annuum L. var. Sweet Banana) hypocotyl cultures during shoot formation

Summary The simultaneous presence of 6-benzyladenine (BA) and sucrose in a Murashige and Skoog medium (SIM) during the initial stages of shoot initiation have been found to be obligatory for high-frequency shoot formation in the Capsicum annuum L. var. Sweet Banana upper hypocotyl explants. The explants are determined for shoot formation following a minimum of 8 days of culture on SIM. Deprivation of exogenous sucrose from day 6 to day 20 of culture had no effect on the shoot forming response of the explants. BA and sucrose appear to act independently on different aspects of the competence of explants to respond to SIM during shoot initiation.Abbreviations BA N⁶-benzyladenine - MS Murashige and Skoog medium - SIM shoot induction medium - HFM hormone free medium - SUC sucrose minus medium     

Studies on Stenostomum grande Child, 1902 (Platyhelminthes,Catenulida): fine structure of the digestive tract and the endocytotic activity of the gastrodermis

Abstract The digestive tract and its endocytotic activity in the catenulid Stenostomum grande were studied by electron microscopy. The pharynx was typical of the simplex type. At the mouth, between the integumental epithelium and the pharyngeal epithelium proper, was a transition zone. Among the epithelial cells of this transition were monociliated sensory cells and the necks of bucco-pharyngeal secretory cells of two types. The pharyngeal epithelium proper was densely ciliated, with long ciliary rootlets and mitochondria. It was surrounded by two layers of muscles. The gastrodermis consisted of phagocytes and typical secretory Minotian cells. It was underlain by a delicate basal lamina and muscle fibers. Distinctive of the phagocytes was the presence of differentiated cilia, cup-shaped mitochondria, and vacuoles with dense inclusions. Morphological differences between pharyngeal and gastrodermal cilia suggest functional differences. Experiments using latex beads as tracers and the identification of acid phosphatase in cytoplasmic vacuoles pointed to a high level of endocytotic and digestive activity in the phagocytes. Our data demonstrate that the basic structure of the digestive tract in S. grande conforms well to that of other free-living platyhelminths, but it does have ultrastructural peculiarities.     

Effects of fire on abundance of Eragrostis intermedia in a semi-arid grassland in southeastern Arizona

Abstract. Eragrostis intermedia (Plains lovegrass) is a midheight perennial bunchgrass native to semi-arid grasslands of the southwestern USA, that becomes an abundant and dominant component of these grasslands in areas long protected from livestock grazing. Substantial mortality of plains lovegrass occurred on a large livestock exclosure in southeastern Arizona, after a period of declining precipitation, but only in areas that had not burned in the previous three years. Lovegrass abundance subsequently increased on both undisturbed and burned sites, but remained substantially higher on the burned area. Long-term abundance of plains lovegrass may depend on episodic fire, particularly during periods of reduced precipitation.     

Effect of titanium dioxide concentration on the survival of Pseudomonas stutzeri during irradiation with near ultraviolet light

Cells of Pseudomonas stutzeri in suspensions of TiO₂ ranging in concentration from 0.5 to 4.0 g l^-1 were irradiated with a blacklight blue u.v. source displaying peak emissivity at approximately 370 mm. Irradiation under these conditions is known to result in the generation of lethal free radicals. During irradiation the suspensions were agitated, using a specially modified laboratory shaker, to ensure efficient exposure of the TiO₂. A u.v. radiation dose of 175 kJ m^-2 resulted in cell fractional survival ranging from 5.5 times 10^-5, at the lowest TiO₂ concentration, to 1.0 times 10^-6, at the highest TiO₂ concentration. The advantages of contactors employing TiO₂ suspensions are briefly compared to immobilized TiO₂ systems.