Greater sensitivity of the vestibulosympathetic reflex in the upright posture in humans.

Otolith organs have been shown to activate the sympathetic nervous system in the prone position by head-down rotation (HDR) in humans. To date, otolithic stimulation by HDR has not been comprehensively studied in the upright posture. The purpose of the present study was to determine whether otolithic stimulation increases muscle sympathetic nerve activity (MSNA) in the upright posture. It was hypothesized that stimulation of the otolith organs would increase MSNA in the upright posture, despite increased baseline sympathetic activation due to unloading of the baroreceptors. MSNA, arterial blood pressure, heart rate, and degree of head rotation were measured during HDR in 18 volunteers (23 +/- 1 yr) in different postures. Study 1 (n = 11) examined HDR in the prone and sitting positions and study 2 (n = 7) examined HDR in the prone and 60 degrees head-up tilt positions. Baseline MSNA was 8 +/- 4, 15 +/- 4, and 33 +/- 2 bursts/min for prone, sitting, and head-up tilt, respectively. HDR significantly increased MSNA in the prone (Delta4 +/- 1 and Delta105 +/- 37% for burst frequency and total activity, respectively), sitting (Delta5 +/- 1 and Delta43 +/- 12%), and head-up tilt (Delta7 +/- 1 and Delta110 +/- 41%; P < 0.05). Sensitivity of the vestibulosympathetic reflex (%DeltaMSNA/DeltaHDR; degree of head rotation) was significantly greater in the sitting and head-up tilt than prone position (prone = 74 +/- 22; sitting = 109 +/- 30; head-up tilt = 276 +/- 103; P < 0.05). These data indicate that stimulation of the otolith organs can mediate increases in MSNA in the upright posture and suggest a greater sensitivity of the vestibulosympathetic reflex in the upright posture in humans.     

Insulin stimulation of GLUT4 exocytosis, but not its inhibition of endocytosis, is dependent on RabGAP AS160

Insulin maintains whole body blood glucose homeostasis, in part, by regulating the amount of the GLUT4 glucose transporter on the cell surface of fat and muscle cells. Insulin induces the redistribution of GLUT4 from intracellular compartments to the plasma membrane, by stimulating a large increase in exocytosis and a smaller inhibition of endocytosis. A considerable amount is known about the molecular events of insulin signaling and the complex itinerary of GLUT4 trafficking, but less is known about how insulin signaling is transmitted to GLUT4 trafficking. Here, we show that the AS160 RabGAP, a substrate of Akt, is required for insulin stimulation of GLUT4 exocytosis. A dominant-inhibitory mutant of AS160 blocks insulin stimulation of exocytosis at a step before the fusion of GLUT4-containing vesicles with the plasma membrane. This mutant, however, does not block insulin-induced inhibition of GLUT4 endocytosis. These data support a model in which insulin signaling to the exocytosis machinery (AS160 dependent) is distinct from its signaling to the internalization machinery (AS160 independent).     

Effects of CO<Subscript>2</Subscript> on the formation of flavour volatiles during fermentation with immobilised brewer’s yeast

Immobilised-cell fermentors offer great benefits compared to traditional free-cell systems. However, a major problem is unbalanced flavour production when these fermentors are used for the production of alcoholic beverages. One of the keys to obtaining better control over flavour formation may be the concentration of dissolved CO₂, which has inhibitory effects on yeast growth and metabolism. This article demonstrates that the presence of immobilisation matrices facilitates the removal of CO₂ from the liquid medium, which results in a low level of dissolved CO₂ during fermentation. Moreover, the formation of volatile higher alcohols and esters was greatly enhanced in the immobilised-cell system when compared to the free cell system. By sparging a CO₂ flow (45 ml/min) into the immobilised-cell system, cell growth was reduced by 10–30% during the active fermentation stage, while the fermentation rate was unaffected. The uptake of branched-chain amino acids was reduced by 8–22%, and the formation of higher alcohols and esters was reduced on average by 15% and 18%, respectively. The results of this study suggest that mismatched flavour profiles with immobilised-cell systems can be adjusted by controlling the level of dissolved CO₂ during fermentation with immobilised yeast.     

Kinetics and mechanism of exogenous anion exchange in FeFbpA–NTA: significance of periplasmic anion lability and anion binding activity of ferric binding protein A

The bacterial transferrin ferric binding protein A (FbpA) requires an exogenous anion to facilitate iron sequestration, and subsequently to shuttle the metal across the periplasm to the cytoplasmic membrane. In the diverse conditions of the periplasm, numerous anions are known to be present. Prior in vitro experiments have demonstrated the ability of multiple anions to fulfill the synergistic iron-binding requirement, and the identity of the bound anion has been shown to modulate important physicochemical properties of iron-bound FbpA (FeFbpA). Here we address the kinetics and mechanism of anion exchange for the FeFbpA–nitrilotriacetate (NTA) assembly with several biologically relevant anions (citrate, oxalate, phosphate, and pyrophosphate), with nonphysiologic NTA serving as a representative synergistic anion/chelator. The kinetic data are consistent with an anion-exchange process that occurs in multiple steps, dependent on the identity of both the entering anion and the leaving anion. The exchange mechanism may proceed either as a direct substitution or through an intermediate FeFbpA–X* assembly based on anion (X) identity. Our kinetic results further develop an understanding of exogenous anion lability in the periplasm, as well as address the final step of the iron-free FbpA (apo-FbpA)/Fe³⁺ sequestration mechanism. Our results highlight the kinetic significance of the FbpA anion binding site, demonstrating a correlation between apo-FbpA/anion affinity and the FeFbpA rate of anion exchange, further supporting the requirement of an exogenous anion to complete tight sequestration of iron by FbpA, and developing a mechanism for anion exchange within FeFbpA that is dependent on the identity of both the entering anion and the leaving anion.     

Discovery of 2-substituted benzoxazole carboxamides as 5-HT3 receptor antagonists

A new class of 2-substituted benzoxazole carboxamides are presented as potent functional 5-HT(3) receptor antagonists. The chemical series possesses nanomolar in vitro activity against human 5-HT(3)A receptors. A chemistry optimization program was conducted and identified 2-aminobenzoxazoles as orally active 5-HT(3) receptor antagonists with good metabolic stability. These novel analogues possess drug-like characteristics and have potential utility for the treatment of diseases attributable to improper 5-HT(3) receptor function, especially diarrhea predominant irritable bowel syndrome (IBS-D).     

Nitrogen Translocation to Fresh Litter in Northern Hardwood Forest

Nitrogen immobilization in fresh litter represents a significant N flux in forest ecosystems, and changes in this process resulting from atmospheric N deposition could have important implications for ecosystem responses. We conducted two leaf decay experiments, using ¹⁵N-labeled sugar maple leaf litter, to quantify N transport from old litter and soil to fresh litter during early stages of decomposition, and we examined the influence of litter N concentration and soil N availability on upward N transfer in a northern hardwood forest. After one year of decay, the average N transfer from soil to fresh litter (2.63 mg N g^?1 litter) was much higher than the N transfer from older litter (1- to 2-years-old) to fresh litter (0.37 mg N g^?1 litter). We calculated the ratio of annual N transfer per unit of excess ¹⁵N pool for these two N sources. The ratio was not significantly different between old litter and soil, suggesting that fungi utilize N in the old litter and mineral soil pools for transport to decaying fresh litter with similar efficiency. Initial litter N concentration had a significant effect on upward N flux into decaying leaf litter, whereas no effect of soil N fertilization was observed. Reduction in the flux from soil to fresh litter owing to anthropogenic N inputs probably contributes significantly to changing soil N dynamics. Future work is needed on fungal N acquisition and transport as well as the fungal taxa involved in this process and their responses to changing environments.     

Gestation as mothering

Some commentators maintain that gestational surrogates are not ‘mothers’ in a way capable of grounding a claim to motherhood. These commentators find that the practices that constitute motherhood do not extend to gestational surrogates. We argue that gestational surrogates should be construed as mothers of the children they bear, even if they fully intend to surrender those children at birth to the care of others. These women stand in a certain relationship to the expected children: they live in changed moral circumstances by reason of their pregnancy, and they engage in the practices said to define motherhood in the post-birth context. By contrast, ovum donors and embryo donors are not similarly ‘mothers’ because they do not find themselves involved in these circumstances. Not all women involved in three-parent in vitro fertilization qualify as mothers either. Given this analysis of mothering, we note that transmen who gestate children are engaged in mothering activity even if they otherwise function as a father to those children. By itself, this defence of the maternity of gestational surrogates does not confer moral title to the children they bear; gestation would not by itself override the contractual arrangements gestational surrogates have made regarding the disposition of their children. This interpretation of gestational surrogates as mothers does, however, undercut cultural understandings of these women as mere ‘vessels’, devoid of entitlement to respect as persons and parents. We also consider the meaning of mothering for ‘brain-dead’ women kept alive to give birth and for the prospect of extracorporeal gestation.     

The γ subunits of the native GABAA/benzodiazepine receptors

Subunit-specific antibodies to all the γ subunit isoforms described in mammalian brain (γ₁, γ_2S, γ_L, and γ₃) have been made. The proportion of GABA_A receptors containing each γ subunit isoform in various brain regions has been determined by quantitative immunoprecipitation. In all tested regions of the rat brain, the γ₁, and γ₃ subunits are present in considerable smaller proportion of GABA_A receptor than the γ₂ subunit. Immunocytochemistry shows that γ₁ immunoreactivity concentrates in the stratum oriens and stratum radiatum of the CA1 region of the hippocampus. In the dentate gyrus, γ₁ immunoreactivity concentrates on the outer 2/3 of the molecular layer coinciding with the localization of the axospinous synapses of the perforant pathway. In contrast, γ₃ immunoreactivity concentrates on the basket cells and other GABAergic local circuit neurons of the hilus. These cells are also rich in γ_2S. In the cerebellu, γ₁ immunolabeling was localized on the Bergmann glia. The γ_2S and γ_2L subunits are differentially expressed in various brain regions. Thus the γ_2S is highly expressed in the olfactory bulb and hippocampus whereas the γ_2L is very abundant in inferior colliculus and cerebellum, particularly in Purkinje cells, as immunocytochemistry, in situ hybridization and immunoprecipitation techniques have revealed. The γ_2S and γ_2L coexist in some brain areas and cell types. Moreover, the γ_2S and γ_2L subunits can coexist in the same GABA_A receptor pentamer. We have shown that this is the case in some GABA_A receptors expressed in cerebellar granule cells. These GABA_A receptors also have α and β subunits forming the pentamer. Immunoblots have shown that the rat γ₁, γ_2S, γ_2L and γ₃ subunits are peptides of 47, 45, 47 and 44 kDa respectively. Results also indicate that there are aging-related changes in the expression of the γ_2S and γ_2L subunits in various brain regions which suggest the existence of aging-related changes in the subunit composition of the GABA_A receptors which in turn might lead to changes in receptor pharmacology. The results obtained with the various γ subunit isoforms are discussed in terms of the high molecular and binding heterogeneity of the native GABA_A receptors in brain. Special issue dedicated to Dr. Kinya Kuriyama