1,946 research outputs found
Filtered screens and augmented Teichm\"uller space
We study a new bordification of the decorated Teichm\"uller space for a
multiply punctured surface F by a space of filtered screens on the surface that
arises from a natural elaboration of earlier work of McShane-Penner. We
identify necessary and sufficient conditions for paths in this space of
filtered screens to yield short curves having vanishing length in the
underlying surface F. As a result, an appropriate quotient of this space of
filtered screens on F yields a decorated augmented Teichm\"uller space which is
shown to admit a CW decomposition that naturally projects to the augmented
Teichm\"uller space by forgetting decorations and whose strata are indexed by a
new object termed partially oriented stratum graphs.Comment: Final version to appear in Geometriae Dedicat
Enumeration of chord diagrams on many intervals and their non-orientable analogs
Two types of connected chord diagrams with chord endpoints lying in a
collection of ordered and oriented real segments are considered here: the real
segments may contain additional bivalent vertices in one model but not in the
other. In the former case, we record in a generating function the number of
fatgraph boundary cycles containing a fixed number of bivalent vertices while
in the latter, we instead record the number of boundary cycles of each fixed
length. Second order, non-linear, algebraic partial differential equations are
derived which are satisfied by these generating functions in each case giving
efficient enumerative schemes. Moreover, these generating functions provide
multi-parameter families of solutions to the KP hierarchy. For each model,
there is furthermore a non-orientable analog, and each such model likewise has
its own associated differential equation. The enumerative problems we solve are
interpreted in terms of certain polygon gluings. As specific applications, we
discuss models of several interacting RNA molecules. We also study a matrix
integral which computes numbers of chord diagrams in both orientable and
non-orientable cases in the model with bivalent vertices, and the large-N limit
is computed using techniques of free probability.Comment: 23 pages, 7 figures; revised and extended versio
Second messenger-activated calcium influx in rat peritoneal mast cells.
To study the regulation of calcium influx in non-excitable cells, membrane currents of rat peritoneal mast cells were recorded using the whole-cell patch-clamp technique. At the same time, intracellular calcium concentration ([Ca2+]i) was monitored via the fluorescent calcium-indicator dye Fura-2, which was loaded into cells by diffusion from the patch pipette. 2. Stimulation of mast cells with secretagogues, such as compound 48/80 or substance P, caused release of Ca2+ from internal stores. In addition, external agonists also induced influx of external calcium in 26% of the cells investigated. The agonist-stimulated Ca2+ influx was increased during membrane hyperpolarization and was associated with small whole-cell currents. 3. Likewise, internal application of inositol 1,4,5-trisphosphate (Ins1,4,5P3:0.5-10 microM) elevated [Ca2+]i due both to release of Ca2+ from internal stores and to influx of external calcium. The Ins1,4,5P3-induced influx was greater at more negative membrane potentials, suggesting that Ins1,4,5P3 opened a pathway through which calcium could enter at a rate governed by its electrochemical driving force. 4. Inositol 1,3,4,5-tetrakisphosphate (Ins1,3,4,5P4) did not induce Ca2+ influx by itself nor did it facilitate or enhance Ins1,4,5P3-induced Ca2+ entry. Calcium influx was also induced by inositol 2,4,5-trisphosphate. Since this inositol phosphate is a poor substrate for Ins1,4,5P3 3-kinase it seems unlikely that Ins1,3,4,5P4 plays a role in the regulation of the Ca2(+)-influx pathway in mast cells. 5. The Ins1,4,5P3-induced Ca2+ influx was associated with whole-cell currents of 1-2 pA or less, with no channel activity detectable in whole-cell recordings. The small size of the whole-cell current suggests either that the Ins1,4,5P3-dependent influx occurs via small-conductance channels that are highly calcium specific or that the influx is not via ion channels. 6. Agonist stimulation also activated large-conductance (ca 50 pS) cation channels, through which divalent cations could permeate; thus, these channels represent a second pathway for Ca2+ influx. The slow speed of activation of the channels by agonists, their activation by internal guanosine 5'-O-(3-thiotriphosphate) (GTP-gamma-S), and the inhibition of agonist activation by internal guanosine 5'-O-(2-thiodiphosphate) (GDP-beta-S) all suggest that the 50 pS channels are regulated by a second messenger and/or a GTP-binding protein. The activity of the 50 pS channel in mast cells is not sensitive to either Ins1,4,5P3 or Ins1,3,4,5P4. Activity of the channel was inhibited by elevated [Ca2+]
Ruminant Nutrition Symposium: Role of fermentation acid absorption in the regulation of ruminal pH1,2
Single seed sorting technology and its interaction with processing for food, malt, feed and industrial markets
Non-Peer Reviewe
Molecular adaptation of ruminal epithelia to highly fermentable diets
Feeding highly fermentable diets to ruminants is one strategy to increase
energy intake. The increase in short-chain fatty acid (SCFA) production and
reduced ruminal pH associated with highly fermentable diets imposes a
challenge to the metabolism and the regulation of intracellular pH homeostasis
of ruminal epithelia. The ruminal epithelia respond to these challenges in a
coordinated manner. Whereas the enlargement of absorptive surface area is well
documented, emerging evidence at the mRNA and transporter and enzyme activity
levels indicate that changes in epithelial cell function may be the initial
response. It is not surprising that gene expression analysis has identified
pathways involved in fatty acid metabolism, ion transport, and intracellular
homeostasis to be the pathways dominantly affected during adaptation and after
adaptation to a highly fermentable diet. These findings are important because
the intraepithelial metabolism of SCFA, particularly butyrate, helps to
maintain the concentration gradient between the cytosol and lumen, thereby
facilitating absorption. Butyrate metabolism also controls the intracellular
availability of butyrate, which is widely regarded as a signaling molecule.
Current data indicate that for butyrate metabolism, 3-hydroxy-3
-methylglutaryl-CoA synthase and acetyl-CoA acetyltransferase are potential
regulatory points with transient up- and downregulation during diet
adaptation. In addition to nutrient transport and utilization, genes involved
in the maintenance of cellular tight junction integrity and induction of
inflammation have been identified as differentially expressed genes during
adaptation to highly fermentable diets. This may have important implications
on ruminal epithelial barrier function and the inflammatory response often
associated with subacute ruminal acidosis. The objective of this review is to
summarize ruminal epithelial adaptation to highly fermentable diets focusing
on the changes at the enzyme and transporter activity levels, as well as the
underlying molecular changes at the mRNA and protein expression levels
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