Restricted postexercise pulmonary diffusion capacity and central blood volume depletion

Hanel, Birgitte, Inge Teunissen, Alan Rabøl,Jørgen Warberg, and Niels H. Secher. Restricted postexercisepulmonary diffusion capacity and central blood volume depletion.J. Appl. Physiol. 83(1): 11-17, 1997.Pulmonary diffusion capacity for carbon monoxide(DL_CO),regional electrical impedance(Z₀), and the distribution oftechnetium-99m-labeled erythrocytes together with concentration ofplasma atrial natriuretic peptide (ANP) were determined before andafter a 6-min "all-out" row in nine oarsmen and in six controlsubjects. Two and one-half hours after exercise in the upright seatedposition,DL_CO wasreduced by 6 (2 to 21; median and range) %, thethoracic-to-thigh electrical impedance ratio(Z_{0 thorax}/Z_{0 thigh})rose by 14 (1 to 29) %, paralleled by a 7 (3 to 11) % decrease and a 3 (5 to 12) % increase in the thoracic and thighblood volume, respectively. These responses were associated with adecrease in the plasma ANP concentration from 15 (13-31) to 12 (9-27) pmol/l (P < 0.05).Similarly, in the supine position,Z_{0 thorax}/Z_{0 thigh}increased by 10 (5 to 28) % whenDL_CO wasreduced 12 (6-26) % (P < 0.05), whereasDL_CO remained stable in the control group. The increase inZ_{0 thorax}/Z_{0 thigh} and the corresponding redistribution of the blood volume in both bodypositions show that approximately one-half of the postexercise reduction ofDL_CO isexplained by a decrease in the pulmonary blood volume. The role of areduced postexercise central blood volume is underscored by the lowerplasma ANP, which aids in upregulating the blood volume after exercisein athletes.

     

Wortmannin inhibits both insulin- and contraction-stimulated glucose uptake and transport in rat skeletal muscle

Wojtaszewski, Jørgen F. P., Bo F. Hansen, BirgitteUrsø, and Erik A. Richter. Wortmannin inhibits both insulin-and contraction-stimulated glucose uptake and transport in rat skeletal muscle. J. Appl. Physiol. 81(4):1501-1509, 1996.The role of phosphatidylinositol (PI) 3-kinasefor insulin- and contraction-stimulated muscle glucose transport wasinvestigated in rat skeletal muscle perfused with a cell-freeperfusate. The insulin receptor substrate-1-associated PI 3-kinaseactivity was increased sixfold upon insulin stimulation but wasunaffected by contractions. In addition, the insulin-stimulated PI3-kinase activity and muscle glucose uptake and transport in individualmuscles were dose-dependently inhibited by wortmannin with one-halfmaximal inhibition values of ~10 nM and total inhibition at 1 µM.This concentration of wortmannin also decreased thecontraction-stimulated glucose transport and uptake by ~30-70%without confounding effects on contractility or on muscle ATP andphosphocreatine concentrations. At higher concentrations(3 and 10 µM), wortmannin completely blocked thecontraction-stimulated glucose uptake but also decreased thecontractility. In conclusion, inhibition of PI 3-kinase with wortmanninin skeletal muscle coincides with inhibition of insulin-stimulated glucose uptake and transport. Furthermore, in contrast to recent findings in incubated muscle, wortmannin also inhibitedcontraction-stimulated glucose uptake and transport. The inhibitoryeffect of wortmannin on contraction-stimulated glucose uptake may beindependent of PI 3-kinase activity or due to inhibition of asubfraction of PI 3-kinase with low sensitivity to wortmannin.

     

Mechanism of third signals provided by IL-12 and OX-40R ligation in eliciting therapeutic immunity following dendritic-tumor fusion vaccination

Dendritic-tumor heterokaryons generated by electrofusion are highly immunogenic. In animal studies, a single vaccination was therapeutic for tumors established in the lung, skin, and brain. However, effective therapy required a third signal which could be provided by exogenous IL-12 or the agonistic anti-OX-40R monoclonal antibody (mAb). In this study, we investigated the mechanism and mode of actions of these two seemingly distinct adjuvants. In immunotherapy of the MCA205 sarcoma, administration of the neutralizing anti-IL-12 mAb nearly completely blocked the adjuvant effect of IL-12, but had minimal inhibitory effects on anti-OX-40R mAb. By contrast, in vivo administration of the antagonistic anti-OX-40L mAb inhibited the adjuvant effects of both IL-12 and anti-OX-40R mAb. Thus, a common pathway of endogenous OX-40 interaction is critical for the development of a therapeutic immune response. Analysis of the third signal mechanism revealed that in the absence of an adjuvant, vaccination with fusion hybrids led to IL-10 production without eliciting IFN-gamma secreting cells. The addition of IL-12 to vaccination suppressed IL-10 production and initiated sensitization of specific IFN-gamma secreting cells, resulting in a type 1-like antitumor immunity. These findings underscore the significance of the third signal in the design of dendritic cell-based cancer vaccines.     

The primary defect in glycogen synthase activity is not based on increased glycogen synthase kinase-3alpha activity in diabetic myotubes

The mechanism responsible for the diminished activation of glycogen synthase (GS) in diabetic myotubes remains unclear, but may involve increased activity and/or expression of glycogen synthase kinase-3 (GSK-3). In myotubes established from type 2 diabetic and healthy control subjects we determined GS activity ratio, protein expression, and activity of GSK-3alpha and beta under basal and insulin-stimulated conditions when precultured in increasing insulin concentrations. In myotubes precultured at low insulin concentrations acute insulin stimulation increased GS activity more in control than in diabetic subjects, whereas the corresponding GSK-3alpha but not GSK-3beta activity was significantly reduced by acute insulin treatment in both groups. However, in myotubes precultured at high insulin concentrations the effect of insulin on GS and GSK-3alpha activity was blunted in both groups. The protein expression of GSK-3alpha or beta was unaffected. In conclusion, myotubes with a primary defect in GS activity express insulin responsive GSK-3alpha, suggesting that failure of insulin to decrease GS phosphorylation involves abnormal activity of another kinase or phosphatase.     

Characterization of sorCS1, an alternatively spliced receptor with completely different cytoplasmic domains that mediate different trafficking in cells

We previously isolated and sequenced murine sorCS1, a type 1 receptor containing a Vps10p-domain and a leucine-rich domain. We now show that human sorCS1 has three isoforms, sorCS1a-c, with completely different cytoplasmic tails and differential expression in tissues. The b tail shows high identity with that of murine sorCS1b, whereas the a and c tails have no reported counterparts. Like the Vps10p-domain receptor family members sortilin and sorLA, sorCS1 is synthesized as a proreceptor that is converted in late Golgi compartments by furin-mediated cleavage. Mature sorCS1 bound its own propeptide with low affinity but none of the ligands previously shown to interact with sortilin and sorLA. In transfected cells, about 10% of sorCS1a was expressed on the cell surface and proved capable of rapid endocytosis in complex with specific antibody, whereas sorCS1b presented a high cell surface expression but essentially no endocytosis, and sorCS1c was intermediate. This is an unusual example of an alternatively spliced single transmembrane receptor with completely different cytoplasmic domains that mediate different trafficking in cells.     

Immunopurification and characterization of rat adipocyte caveolae suggest their dissociation from insulin signaling

Adipocytes play an important role in the insulin-dependent regulation of organismal fuel metabolism and express caveolae at levels as high or higher than any other cell type. Recently, a link between insulin signaling and caveolae has been suggested; nevertheless, adipocyte caveolae have been the subject of relatively few studies, and their contents have been minimally characterized. With the aid of a new monoclonal antibody, we developed a rapid procedure for the immunoisolation of caveolae derived from the plasma membrane of adipocytes, and we characterized their protein content. We find that immunopurified adipocyte caveolae have a relatively limited protein composition, and they lack the raft protein, flotillin, and insulin receptors. Immunogold labeling and electron microscopy of the adipocyte plasma membrane confirmed the lack of insulin receptors in caveolae. In addition to caveolins, the structural components of caveolae, their major protein constituents, are the semicarbazide-sensitive amine oxidase and the scavenger lipoprotein receptor CD36. The results are consistent with a role for caveolae in lipid flux in and of adipocytes.     

Resource partitioning on basis of hydrolytic enzymes in deposit-feeding mud snails (Hydrobiidae)

Summary Crude extracts of hydrolytic enzymes from the related mud snailsHydrobia ulvae, H. ventrosa andH. neglecta are compared by use of six different methods and 18 natural carbohydrates. Synthetic substrates for linkage specific carbohydrases and trypsin-like activity were studied in addition to lysozyme-like activity.A significant hydrolysis was only observed with the reserve carbohydrates amylose, glycogen and laminaran. Many algal carbohydrates were, however, digested to some extent.The qualitative spectra are almost identical for the three species but significant quantitative differences were found. The findings are discussed in relation to information on the chemical composition of potential food items and it is concluded that the commonly observed coexistence of the snails can in part be explained by selection for microalgae and detritus particularly meeting their enzymatic potentials.     

Regulation of phosphoinositide 3-kinase by its intrinsic serine kinase activity in vivo

One potentially important mechanism for regulating class Ia phosphoinositide 3-kinase (PI 3-kinase) activity is autophosphorylation of the p85 alpha adapter subunit on Ser608 by the intrinsic protein kinase activity of the p110 catalytic subunit, as this downregulates the lipid kinase activity in vitro. Here we investigate whether this phosphorylation can occur in vivo. We find that p110 alpha phosphorylates p85 alpha Ser608 in vivo with significant stoichiometry. However, p110 beta is far less efficient at phosphorylating p85 alpha Ser608, identifying a potential difference in the mechanisms by which these two isoforms are regulated. The p85 alpha Ser608 phosphorylation was increased by treatment with insulin, platelet-derived growth factor, and the phosphatase inhibitor okadaic acid. The functional effects of this phosphorylation are highlighted by mutation of Ser608, which results in reduced lipid kinase activity and reduced association of the p110 alpha catalytic subunit with p85 alpha. The importance of this phosphorylation was further highlighted by the finding that autophosphorylation on Ser608 was impaired, while lipid kinase activity was increased, in a p85 alpha mutant recently discovered in human tumors. These results provide the first evidence that phosphorylation of Ser608 plays a role as a shutoff switch in growth factor signaling and contributes to the differences in functional properties of different PI 3-kinase isoforms in vivo.     

Complex epidermal organs of Phascolion (Sipuncula): insights into the evolution of bimodal secretory cells in annelids

The epidermal organs of an undescribed Phascolion species from the Balearic Islands were investigated using SEM, TEM, LM, CLSM and μCT methods. We found axial receptor cells confirming the previously assumed sensory function of epidermal organs. Our analyses also revealed six types of secretory cells. Some secretory cells types are capable of secreting filamentous and amorphous secretion in two different ways simultaneously (bimodal secretion). The high diversity of cell types, the complex pattern of acinar units, and the absence of a common gland pore make epidermal organs of Phascolion unique amongst sipunculans (Phascolion type). Our reconstruction of the evolution of the epidermal organs of Sipuncula revealed that Phascolion‐type epidermal organs may have derived from either Golfingia‐, Sipunculus‐ or Phascolosoma‐type epidermal organs. The oldest known sipunculans were Golfingia‐like and had epidermal organs, which might resemble the architecture of the Golfingia‐type epidermal organs in extant taxa. Thus, it can be hypothesized that bimodal secretory cells (e.g. basophilic secretory cells) were part of the sipunculan ground pattern. Moreover, bimodal secretory cells of Phascolion look strikingly similar to those found in various annelid glands and thus might even be part of the ground pattern of stem species of Sipuncula + Pleistoannelida.