Cobaltocene reductions of multiply bonded dirhenium complexes. II. The isolation of the paramagnetic species [(η5-C5H5)2Co][Re2(hp)4X2] (hp = anion of 2-hydroxypyridine; X = Cl,Br, or I)

Reaction of the quadruply bonded dirhenium(III) complexes (n-Bu₄N)₂Re₂X₈ (X = Cl, Br, or I) with 2-hydroxypyridine (Hhp) in refluxing n-pentanol gives Re₂(hp)₄X₂ in high yield (>;90%). These complexes are reduced by cobaltocene to yield the paramagnetic salts [(η⁵-C₅H₅)₂Co][Re₂(hp)₄X₂]. The spectroscopic (electronic absorption and infrared) and electrochemical properties of these sets of complexes are in accord with them possessing σ²π⁴δ²(Re₂⁶⁺) or σ²π⁴δ²δ*¹(Re₂⁵⁺ ground state electronic configurations.     

Comparison of endogenous phosphorylation of hen and rat spinal cord proteins and partial characterization of optimal phosphorylation conditions for hen spinal cord

The optimal conditions for the endogenous phosphorylation of hen spinal cord cytosolic and membrane proteins with 5 μM [γ-³²P]ATP, 10 mM MgCl₂, were determined by 10% SDS-polyacrylamide gel electrophoresis, autoradiography, and microdensitometry. Phosphate incorporation increased linearly with concentrations ranging from 35–75 μg/100 μl for cytosolic proteins and 21–125 μg/200 μl for membrane proteins. Optimal incubation times, temperatures, and pH values were 60 s, 30°C, and 6.0, respectively, for spinal cord cytosolic proteins and 15 s, 45°C, and 8.0, respectively, for spinal cord membranes. Prominent species differences in protein phosphorylation between these fractions in hens and similarly prepared fractions in rats, co-electrophoresed, include 80K and 30K protein phosphate acceptors unique to rat spinal cord cytosol, 60K and 16K protein phosphate acceptors characteristic of rat spinal cord membranes, a 50K protein phosphate acceptor present only in hen spinal cord membranes, and greater phosphorylation of a more abundant 20K protein in both hen spinal cord fractions. The functional significance of these differences is presently unclear. However, their characterization provides a basis from which to launch future investigations of the biochemistry, pharmacology, and toxicology of spinal cord protein phosphorylation and indicates that caution should be exercised in the choice of an animal model with characteristics appropriate to those of the system it is representing.     

Sorting during transport to the surface of PC12 cells: divergence of synaptic vesicle and secretory granule proteins

PC12 cells, a cell line derived from a rat pheochromocytoma, have both regulated and constitutive secretory pathways. Regulated secretion occurs via large dense core granules, which are related to chromaffin granules and are abundant in these cells. In addition, PC12 cells also contain small electron-lucent vesicles, whose numbers increase in response to nerve growth factor and which may be related to cholinergic synaptic vesicles. These could characterize a second regulated secretory pathway. We have investigated the trafficking of protein markers for both these organelles. We have purified and characterized the large dense core granules from these cells using sequential velocity and equilibrium gradients. We demonstrate the copurification of the major PC12 soluble regulated secretory protein (secretogranin II) with this organelle. As a marker for the synaptic vesicle-like organelles in this system, we have used the integral membrane glycoprotein p38 or synaptophysin. We show that the p38-enriched fraction of PC12 cells comigrates with rat brain synaptic vesicles on an equilibrium gradient. We also demonstrate that p38 purifies away from the dense core granules; less than 5% of this protein is found in our dense granule fraction. Finally we show that p38 does not pass through the dense granule fraction in pulse-chase experiments. These results rule out the possibility of p38 reaching the small clear vesicles via mature dense granules and imply that these cells may have two independently derived regulated pathways.     

Diagnoses and key to the genera of the Gracilariaceae (Gracilariales,Rhodophyta)

A key to the genera of the Gracilariaceae is provided along with a short diagnosis for each genus. Features of the mature cystocarp and spermatangial configurations that separate genera are illustrated.     

Antitrssanspirant action of abscisic acid and ten synthetic analogs in black spruce

A rapid screening procedure was developed to compare the antitranspirant action of abscisic acid (ABA) and ten synthetic analogs under well-watered and droughted conditions. Compounds were applied to black spruce [ Picea mariana (Mill.) B.S.P.] seedlings at 10 μ M using an aerated root drench. The plants were grown aeroponically under a continuous mist in a misting chamber and a drought stress was then applied, 7 days after treatment with the growth regulators, by switching off the misting unit for 2 h. The activity of 2- cis and 2- trans isomers of 4- transepoxy –β-ionylideneacetic acid, their corresponding methyl esters, and 4 acetylenic analogs were compared with ABA and control, untreated seedlings. Stomatal conductance and transpiration rates declined in treated seedlings after 3 h, but returned to pre-treatment levels 2–7 days after treatment. However, transpiration declined significantly as a result of ABA- and analog-treated seedlings when they were drought stressed 7 days after treatment. Since transpiration declined more than net photosynthesis, water use efficiency increased by up to 75% as a result of ABA analog treatment. The 2- cis -isomers of epoxy-β-ionylideneacetic acids and acetylenic alcohol analogs reduced transpiration and improved water use efficiency more than ABA and 3 out of the 4 2- trans isomers.     

Zooplankton abundance and evidence for its reduction by macrophyte mats in two Orinoco floodplain lakes

Zooplankton populations were sampled over one annual cycle intwo floodplain lakes of the Orinoco River, Venezuela, in anattempt to establish the relationship between abundance patternsand the hydrology and morphometry of the lakes. One of the lakes(Tineo) is relatively large with a gently sloping basin; theother one (Aguilera) is smaller and channel-shaped. The hydraulicresidence time of Lake Aguilera during inundation by the riveris shorter (<1 day) than the minimum generation times ofcrustacean (4–12 days) and rotiferan (2.5 days) zooplankton.For Lake Tineo, residence time during inundation (7 days) islonger than generation times for all taxa except copepods. AlthoughLake Aguilera receives water from Lake Tineo during inundation,zooplankton densities were greatly reduced during passage througha large bed of the floating aquatic grass Paspalum repens locatednear the outlet of Lake Tineo. This retention was not size-selectiveand affected phytoplankton as well as zooplankton. In the Orinocofloodplain zooplankton densities are affected not only by hydraulicresidence times but also by passage of water between lakes,which exposes populations to large losses within macrophytebeds. Retention of plankton by floating macrophyte beds is potentiallyimportant to the trophic ecology of tropical floodplain lakesbecause it results in the concentration of planktonic productionin epiphytic and benthic habitats, where it can readily supportfood webs consisting of macroinvertebrates and fishes. Exportof plankton from floodplain waterbodies to the river is alsoreduced by this mechanism. ¹Present address: Department of Biological Sciences, Universityof California, Santa Barbara, CA 93106, USA     

Cytochemical localization of adenylate cyclase in the dense tubule system of human blood platelets stimulated by forskolin, prostacyclin and prostaglandin D2

Platelets were briefly fixed in paraformaldehyde/glutaraldehyde and then incubated with 5'-adenylyl imidodiphosphate under conditions suitable for the cytochemical detection of adenylate cyclase activity. The adenylate cyclase activity of these platelets retains the ability to respond to prostaglandins E1, D2, I2 (prostacyclin), forskolin and fluoride. Sites of stimulated adenylate cyclase activity were localized cytochemically by the reaction of lead with the reaction product imidodiphosphate to form deposits of lead imidodiphosphate that are visible in the electron microscope. Reaction product deposition was seen only in the dense tubule system of human platelets when the incubation medium contained forskolin, prostacyclin, or prostaglandin D2 at concentrations known to stimulate the enzyme in intact platelets. Epinephrine, an antagonist of adenylate cyclase inhibited the cytochemical reaction stimulated by prostacyclin. The fact that the cytochemical reaction was induced by agonists that stimulate the enzyme through two different types of prostaglandin receptors and by forskolin, which acts distal to the receptors, confirms that the method specifically detects adenylate cyclase. The presence of adenylate cyclase in the dense tubules may be significant for the regulation of intracellular Ca2+ and arachidonic acid metabolism by this membrane system.     

Experimental allergic orchitis in mice

Inbred strains of mice were studied for their susceptibility to the induction of experimental allergic orchitis after sensitization with mouse testicular homogenate in complete Freund's adjuvant accompanied by injections of extract from Bordetella pertussis. Susceptibility to autoimmune orchitis was found to be linked to the major histocompatibility complex in BALB/c and C57BL/10 mice and mapped to genes encoded within the H-2D ^dregion. In five of six groups of bidirectional (susceptible × resistant) F₁ hybrids, H-2D ^d-linked susceptibility was inherited as a dominant autosomal trait. However, in (BALB/cByJ × DBA/2J)F₁ and (DBA/2J × BALB/cByJ)F₁ hybrids, dominant autosomal resistance to the induction of autoimmune orchitis was observed. Backcross analysis between the resistant F₁ hybrid and the susceptible BALB/cByJ parent suggests that a single independently segregating DBA/2J locus is capable of negating H-2D ^d-linked susceptibility, and controls resistance to the induction of autoimmune orchitis.Abbreviations used in this paper BP extract Bordetella pertussis extract - CFA complete Freund's adjuvant - EAO experimental allergic orchitis - Ir immune response - MHC major histocompatibility complex - MLH mouse liver homogenate - MTH mouse testis homogenate - PI pathology index     

Muscle glycogen synthesis after exercise: effect of time of carbohydrate ingestion

The time of ingestion of a carbohydrate supplement on muscle glycogen storage postexercise was examined. Twelve male cyclists exercised continuously for 70 min on a cycle ergometer at 68% VO2max, interrupted by six 2-min intervals at 88% VO2max, on two separate occasions. A 25% carbohydrate solution (2 g/kg body wt) was ingested immediately postexercise (P-EX) or 2 h postexercise (2P-EX). Muscle biopsies were taken from the vastus lateralis at 0, 2, and 4 h postexercise. Blood samples were obtained from an antecubital vein before and during exercise and at specific times after exercise. Muscle glycogen immediately postexercise was not significantly different for the P-EX and 2P-EX treatments. During the first 2 h postexercise, the rate of muscle glycogen storage was 7.7 mumol.g wet wt-1.h-1 for the P-EX treatment, but only 2.5 mumol.g wet wt-1.h-1 for the 2P-EX treatment. During the second 2 h of recovery, the rate of glycogen storage slowed to 4.3 mumol.g wet wt-1.h-1 during treatment P-EX but increased to 4.1 mumol.g wet wt-1.h-1 during treatment 2P-EX. This rate, however, was still 45% slower (P less than 0.05) than that for the P-EX treatment during the first 2 h of recovery. This slower rate of glycogen storage occurred despite significantly elevated plasma glucose and insulin levels. The results suggest that delaying the ingestion of a carbohydrate supplement post-exercise will result in a reduced rate of muscle glycogen storage.     

Palynological evidence of Azolla nilotica Dec. in recent Holocene of the eastern Nile Delta and palaeoenvironment

Megaspores, microspores and massulae of the free-floating fern, Azolla nilotica, were found in Late Holocene sediments obtained by coring in the eastern Nile Delta. Nowadays, the nearest station for this fern is southern Sudan. The determination of the species is based on spiny projections on the megaspore body and on the verrucate microspores. Palynological studies reveal that the habitat of the fern consisted of extensive papyrus marshes, now disappeared. Several causes for the disappearance of the fern from the Nile Delta are proposed amongst which the most probable is human influence which has completely modified the vegetation and the hydrology.