Consumption of leaf detritus by a stream shredder: Influence of tree species and nutrient status

Four species of riparian vegetation (alder, birch, willow and poplar) were fertilized with nitrogen, phosphorus, nitrogen + phosphorus, or no fertilizer (control). The resulting leaf detritus (leached but not microbially colonized) was offered to a stream shredder, Hydatophylax variabilis (Trichoptera: Limnephilidae). In one experiment, shredder consumption of leaf detritus from different nutrient treatments (within tree species) was compared, and in a second experiment, consumption of different tree species (within nutrient treatments) was compared. Larvae preferred leaf detritus from nitrogen + phosphorus treatments (except in poplar where nitrogen treatment was preferred). Alder was preferred over other tree species for all treatments. Chemical and physical analyses of leaf litter showed differences between tree species and nutrient treatments in nutrient content, tannins and leaf toughness. Leaf consumption by larvae was positively associated with nitrogen content and negatively associated with condensed tannin content. Species composition and nutrient status of riparian vegetation may strongly influence detrital food webs in streams.     

Interactions ofCandida albicans with bacteria and salivary molecules in oral biofilms

The yeastCandida albicans coaggregates with a variety of streptococcal species, an interaction that may promote oral colonization by yeast cells.C. albicans andCandida tropicalis are the yeasts most frequently isolated from the human oral cavity and our data demonstrate that both these species bind toStreptococcus gordonii NCTC 7869 while two otherCandida species (Candida krusei andCandida kefyr) do not. Adherence ofC. albicans was greatest when the yeast had been grown at 30° C to mid-exponential growth phase. For 21 strains ofC. albicans there was a positive correlation between the ability to adhere toS. gordonii and adherence to experimental salivary pellicle. Whole saliva either stimulated or slightly inhibited adherence ofC. albicans toS. gordonii depending on the streptococcal growth conditions. The results suggest that the major salivary adhesins and coaggregation adhesins ofC. albicans are co-expressed.     

Pertussis toxin blocks the inhibitory effect of muscarinic cholinergic agonists on cyclic AMP accumulation and prolactin secretion in GH3 anterior-pituitary tumour cells.

The inhibition of prolactin secretion and cyclic AMP accumulation in GH3 cells by muscarinic agonists was blocked by preincubation of the cells with pertussis toxin (islet-activating protein). There was a lag of approx. 80 min in the onset of the effect on secretion. These results suggest that muscarinic agonists decrease prolactin secretion by inhibiting adenylate cyclase activity.     

Management of radiation necrosis and advanced cancer of the chest wall in patients with breast malignancy.

Aggressive resection, with individualized reconstruction by several methods, is of value in many patients with radiation necrosis and/or advanced breast cancer of the chest wall. Although this does not always significantly lengthen survival, it can improve the quality of life markedly in many instances. Remarkably large defects can be reconstructed with single-stage procedures.     

Studies of ANF processing and secretion using a primary cardiocyte culture model.

In contrast to most other endocrine peptides ANF is stored in the heart as part of a larger prohormone, often called pro-ANF, yet is found in the circulation as a 28 amino acid peptide, called ANF. It has been shown that the conversion of the 126 amino acid pro-ANF to ANF occurs in the heart. This paper summarizes studies from our laboratory that have used a primary neonatal rat heart cell culture system to investigate the location and mechanism of this relatively unusual processing event. We have found that in culture the maintenance of the cells in a glucocorticoid-containing serum-free medium is required to observe processing as occurs in vivo. The cells contain the prohormone while ANF accumulates in the medium. Various experiments with protease inhibitors, pulse-chase biosynthetic labeling, incubation of cells with ANF-related peptides, and enrichment of cultures for myocytes have resulted in our conclusion that the processing of pro-ANF takes place most likely within the cardiac myocyte just prior to, but in concert with secretion. We have expanded on the use of this processing-competent atrial myocyte culture system to investigate mechanisms of stimulated ANF secretion. It has been shown that the activation of several phospholipase C-coupled receptors (e.g., alpha 1-adrenergic and endothelin receptors) produces a robust release of ANF, but only in cultures that have been maintained under appropriate conditions. Further, it is apparent that the phenylephrine- or endothelin-mediated release of ANF depends in part on influx of extracellular calcium (Ca2+o), while the remaining component of stimulated release may depend on mobilization of intracellular calcium. It also appears that these agonists produce an initial phase of stimulated release, occurring within the first 5 min of agonist exposure, independent of Ca2+o, and a sustained phase that persists as long as the agonists remain on the cells, and depends on the presence of Ca2+o and thus calcium influx. Taken together our studies indicate that the hormonal environment may be an important factor directing the development of differentiated endocrine functions by atrial myocytes and may be involved in the regulation of ANF expression, biosynthesis, and secretion.     

A spectroscopic and conformational study of pertussis toxin

The conformation of native pertussis toxin has been investigated by secondary structure prediction and by circular dichroism, fluorescence and second-derivative ultraviolet absorption spectroscopy. The far-ultraviolet circular dichroic spectrum is characteristic of a protein of high beta-sheet and low alpha-helix content. This is also shown by an analysis of the circular dichroic spectrum with the Contin programme which indicates that the toxin possesses 53% beta-sheet, 10% alpha-helix and 37% beta-turn/loop secondary structure. Second-derivative ultraviolet absorption spectroscopy suggests that 34 tyrosine residues are solvent-exposed and quenching of tryptophan fluorescence emission has shown that 4 tryptophan residues are accessible to iodide ions. One of these tryptophans appears to be in close proximity to a positively charged side-chain, since only 3 tryptophans are accessible to caesium ion fluorescence quenching. When excited at 280 nm, the emission spectrum contains a significant contribution from tyrosine fluorescence, which may be a consequence of the high proportion (55%) of surface-exposed tyrosines. No changes in the circular dichroic spectra of the toxin were found in the presence of the substrate NAD. However, NAD did quench both tyrosine and tryptophan fluorescence emission but did not change the shape of the emission spectrum, or the accessibility of the tryptophans to either the ionic fluorescence quenchers or the neutral quencher acrylamide.     

Control of cell volume in the J774 macrophage by microtubule disassembly and cyclic AMP

We have explored the possibilities that cell volume is regulated by the status of microtubule assembly and cyclic AMP metabolism and may be coordinated with shape change. Treatment of J774.2 mouse macrophages with colchicine caused rapid microtubule disassembly and was associated with a striking increase (from 15-20 to more than 90 percent) in the proportion of cells with a large protuberance at one pole. This provided a simple experimental system in which shape changes occurred in virtually an entire cell population in suspension. Parallel changes in cell volume could then be quantified by isotope dilution techniques. We found that the shape change caused by colchicine was accompanied by a decrease in cell volume of approximately 20 percent. Nocodozole, but not lumicolchicine, caused identical changes in both cell shape and cell volume. The volume loss was not due to cell lysis nor to inhibition of pinocytosis. The mechanism of volume loss was also examined. Colchicine induced a small but reproducible increase in activity of the ouabain-sensitive Na(+), K(+)-dependent ATPase. However, inhibition of this enzyme/transport system by ouabain did not change cell volume nor did it block the colchicines-induced decrease in volume. One the other hand, SITS (4’acetamido, 4-isothiocyano 2,2’ disulfonic acid stilbene), an inhibitor of anion transport, inhibited the effects of colchicines, thus suggesting a role for an anion transport system in cell volume regulation. Because colchicine is known to activate adenylate cyclase in several systems and because cell shape changes are often induced by hormones that elevate cyclic AMP, we also examined the effects of cyclic AMP on cell volume. Agents that act to increase syclic AMP (cholera toxin, which activates adenylate cyclase; IBMX, and inhibitor of phosphodiesterase; and dibutyryl cyclic AMP) all caused a volume decrease comparable to that of colchicine. To define the effective metabolic pathway, we studied two mutants of J774.2, one deficient in adenylate cyclase and the other exhibiting markedly reduced activity of cyclic AMP-dependent protein kinase. Cholera toxin did not produce a volume change in either mutant. Cyclic AMP produced a decrease in the cyclase-deficient line comparable to that in wild type, but did not cause a volume change in the kinase- deficient line. This analysis established separate roles for cyclic AMP and colchicine. The volume decrease induced by cyclic AMP requires the action of a cyclic AMP-dependent protein kinase. Colchicine, on the other hand, induced a comparable volume change in both mutants and wild type, and thus does not require the kinase.     

Membrane behavior of exocytic vesicles: II in fate of the trichocyst membranes in paramecium after induced trichocyst discharge

A specific exocytic process, the discharge of spindle trichocysts of paramecium caudatum was examined by means of the electron microscope. This exocytosis is induced by an electric shock simultaneously in nearly all of the trichocysts (ca. 6,000-8,0000 of a single cell. Single paramecia were subjected to the shock and then fixed at defined times after the shock so that the temporal sequence of the pattern of changes of the trichocyst membranes after exocytosis could be studied. The trichocyst vacuoles fuse with the plasma membrane only for that length of time required for expulsion to take place. After exocytosis, the membrane of the vacuole does not become incorporated into the plasma membrane; rather, the collapsed vacuole is pinched off and breaks up within the cytoplasm. The membrane vesiculates into small units which can no longer be distinguished from vesicles of the same dimensions that exist normally within the cell's cytoplasm. the entire process is completed within 5-10 min. These results differ from the incorporation of mucocyst membranes into the plasma membrane as proposed for tetrahymena.