The characteristics of liver glucose-6-phosphatase in the envelope of isolated nuclei and microsomes are identical

We have compared the characteristics of glucose-6-phosphatase (EC 3.1.3.9) in the envelope of purified nuclei and microsomes from rat liver. The latency of mannose-6-P hydrolysis, permeability to EDTA, and susceptibility of the enzyme to protease-mediated inactivation all indicated that the permeability barrier defined by the envelope in situ is significantly disrupted in isolated nuclei (i.e. in vitro). Latency of mannose-6-P hydrolysis was demonstrated to provide a quantitative measure of the degree of nuclear membrane disruption. Electron micrographs confirmed the existence of substantial regions of the envelope in vitro where the permeability barrier to EDTA was intact (i.e. an "intact component"). The kinetics of glucose-6-phosphatase catalyzed by the intact component was obtained by subtracting the contribution of enzyme in disrupted regions from the total enzymic activity of untreated nuclei. The characteristics of glucose-6-phosphatase in intact and fully disrupted membranes of nuclei were indistinguishable from microsomes with respect to (a) the kinetics of glucose-6-P hydrolysis, (b) the effects of incubations with mannose-6-P, N-ethylmaleimide, and protease from Bacillus amyloliquefaciens, (c) the extremely high latency of carbamyl phosphate:glucose phosphotransferase activity, and (d) both the patterns of response of activity and the change in latency of glucose-6-phosphatase induced by fasting, experimental diabetes, and cortisol injection. Our results show clearly that apparent differences in the glucose-6-phosphatase activity of untreated preparations of nuclei and microsomes are simply expressions of significant differences in the degree of intactness of their respective permeability barriers. Since flattened cisternae, characteristic of the rough endoplasmic reticulum in situ, are preserved in intact regions of the envelope of isolated nuclei, the present findings constitute the most direct and definitive evidence to date that the properties of glucose-6-phosphatase in the endoplasmic reticulum in situ are faithfully reproduced with intact microsomes.     

Evidence for the participation of independent translocation for phosphate and glucose 6-phosphate in the microsomal glucose-6-phosphatase system. Interactions of the system with orthophosphate, inorganic pyrophosphate, and carbamyl phosphate

The interactions of Pi, PPi, and carbamyl-P with the hepatic glucose-6-phosphatase system were studied in intact and detergent-disrupted microsomes. Penetration of PPi and carbamyl-P into intact microsomes was evidenced by their reactions with the enzyme located exclusively on the luminal surface. Lack of effects of carbonyl cyanide m-chlorophenylhydrazone and valinomycin + KCl indicated that pH gradients and/or membrane potentials that could influence the kinetics of the system are not generated during metabolism of PPi and glucose-6-P by intact microsomes. With disrupted microsomes, only competitive interactions were seen among glucose-6-P, Pi, PPi, and carbamyl-P. With intact microsomes, Pi, PPi, and carbamyl-P were relatively weak, noncompetitive inhibitors of glucose-6-phosphatase, and PPi hydrolysis was inhibited competitively by Pi and carbamyl-P but noncompetitively by glucose-6-P. Analysis of the kinetic data in combination with findings from other studies that a variety of inhibitors of the glucose-6-P translocase (T1) does not affect PPi hydrolysis provide compelling evidence that permeability of microsomes to Pi, PPi, and carbamyl-P is mediated by a second translocase (T2). Some properties of the microsomal anion transporters are described. If the characteristics of the glucose-6-phosphatase system as presently defined in intact microsomes apply in vivo, glucose-6-P hydrolysis appears to be the predominant, if not the exclusive, physiologic function of the system. Both the "noncompetitive character" and the relative ineffectiveness of Pi as an inhibitor of glucose-6-phosphatase of intact microsomes result from the rate limitation imposed by T1 that prevents equilibration of glucose-6-P across the membrane. In microsomes from fed rats, where T1 is less rate restricting, about one-half as much Pi was required to give 50% inhibition compared with microsomes from fasted or diabetic rats. Thus, any treatment or agent that alters the kinetic relationship between transport and hydrolysis of glucose-6-P (e.g. endocrine or nutritional status) is an essential consideration in analyses of kinetic data for the glucose-6-phosphatase system.     

The ecology of Hypogeomys antimena, an endemic Madagascan rodent

The subfamily Nesomyinae comprises 11 species of rodents endemic to the island of Madagascar. They show considerable ecological and anatomical diversity but little is known of their biology and they have not been studied to any extent in the wild. We present here the results of a nine-week field study of Hypogeomys antimena , the largest of the Nesomyinae, found only in a restricted area of dry deciduous forest in western Madagascar. Radiotracking data gave a mean home range estimate of 3.5+0.71 ha for 10 animals (five males, five females). Individuals from the same burrow had highly overlapping ranges but ranges of animals from neighbouring burrows showed minimal overlap. We suggest that H. antimena lives in social units, probably consisting of a pair plus their offspring, which occupy exclusive territories. A mark/recapture study gave a minimum population estimate of 48 animals/km² in the study site. The conservation of the species is discussed with reference to its limited distribution and current habitat degradation in the area.     

The interoceptive cue properties of ghrelin generalize to cues produced by food deprivation

A number of recent studies implicate the gut-brain peptide ghrelin as a putative "hunger signal". Most of these studies, however, rely on either consummatory behavior (in humans or nonhuman animals) or self-report (in humans) to draw conclusions regarding the orexigenic properties of this peptide. The present study employs the deprivation intensity discrimination paradigm to assess the interoceptive sensory properties of ghrelin in rats. In this paradigm, one group of rats was placed in a training context and presented with sucrose pellets when 24 h food deprived, but not when 1 h food deprived (24+ group). A second group was trained using the opposite sucrose-deprivation level contingency (1+ group). Learning in this paradigm was demonstrated by animals approaching the food delivery location more frequently under their rewarded compared to their non-rewarded deprivation condition (prior to actual pellet delivery). After asymptotic performance of this discrimination was achieved, these animals (1 h food deprived) were administered ghrelin or saline, either i.p. (3 or 6 nmol) or i3vt (0.1 or 1 nmol), placed in the training context, and appetitive responses were measured. Testing was conducted in extinction, eliminating confounding effects of food consumption. Results of these tests showed that 6 nmol i.p. ghrelin and 0.1 and 1 nmol i3vt ghrelin all generalized to a state of 24 h food deprivation, indicating that exogenous ghrelin has sensory properties in common with the stimuli produced by 24 h food deprivation. These results support the notion that endogenous ghrelin contributes to an interoceptive hunger cue, and that this may be a mechanism by which ghrelin influences food intake and appetitive behavior.     

Partial dentures as an independent indicator of root caries risk in a group of older adults.

Objectives: To estimate the independent association between the wearing of removable partial dentures (RPD) and the presence of root caries in a population of older adults. Design: Multivariate logistic regression modeling of root caries prevalence using different measures of root caries as dependent variables. The model included measures of disease history as indicators of historical risk. Setting: Data collected in the field from three areas of England. Subjects: Random sample of adults aged 60 years and over, drawn from lists of patients registered with general medical practitioners. Intervension: Field measurements of a range of oral health variables including oral disease, disease history, oral status and various social and demographic measures. Main outcome measures: The presence of root caries, unsound and sound root restorations. Results: Of the five different models of root caries prevalence which were used, RPDs featured as an independent risk indicator for root surface cades in the three which were related to the presence of untreated disease. The odds ratios for the contribution made by RPDs were all over 1.6, and when considered alone was in excess of 2 in one model. These models were generally well fitting. RPDs did not feature as a risk indicator in the two models which related only to the presence of root surface restorations. Conclusions: In this study, where RPDs were present, the odds of untreated disease being present increased substantially     

Differential vulnerability to predation and refuge use in competing larval salamanders

The aquatic larvae of two species of salamanders coexist as a result of differences in their competitive abilities: Ambystoma talpoideum is a superior aggressor, whereas A. maculatum is a superior forager. I examined the behavioral mechanisms that permit these species to coexist with their predatory congener, A. opacum. I asked whether the two prey species differ in their vulnerability to predation and in their use of structural and spatial refugia when under the risk of predation; such inter-specific variation may allow predation to contribute indirectly to prey coexistence. Larval A. maculatum (the superior forager) was more vulnerable to predation by A. opacum than was A. talpoideum, and only the latter species significantly increased its use of structural refugia (leaf litter) in the presence of the predator. In pond enclosures, both species of prey exhibited diel patterns of microhabitat use; significantly more larvae occupied shallow regions of enclosures during the day and migrated to deeper water (a spatial refugium) at night. However, when considered separately, neither (1) the presence of a predatory larval A. opacum nor (2) an increased density of intra- and interspecific competitors significantly altered this habitat shift for either prey species. Rather, diel microhabitat usage in A. talpoideum was significantly affected by an interaction between predator presence and competitor density. My results demonstrate the importance of refugia to coexistence in this predator-prey assemblage. Furthermore, predation by A. opacum may mediate prey competition; that is, preferential consumption of A. maculatum may reduce the competitive impact of this superior forager on A. talpoideum, thus enhancing their coexistence.     

Neck spine protects Daphnia pulex from predation by Chaoborus, but individuals with longer tail spine are at a greater risk

We tested the prey preference of Chaoborus sp. on Daphnia pulexwith different defensive morphologies. The protective functionof inducible morphological defences, such as neck spine andlonger tail spine, was evaluated Second instar D.pulex individualsof two clones differing in their strength of neck spine inductionwere offered as prey to both Chaoborus obscuripes and Chaoborusflavicans. We used logistic regression analysis to evaluatethe effect of morphometry on the vulnerability of Daphnia. Thepresence of a neck spine and increased total length protectedD.pulex from Chaoborus predation. However, individuals witha longer tail spine were more vulnerable to Chaoborus predationChaoborus obscuripes was able to eat daphnids with a neck spinedue to the larger gape size of this chaoborid. The smaller speciesC.flavicans almost always ate prey with no neck spine.     

Gall mite (Eriophyes laevis) infestation and leaf removal affect growth of leaf area in black alder (Alnus glutinosa) short shoots

Summary We measured the effects ofEriophyes laevis mite galls on the relative growth of short shoot leaf area ofAlnus glutinosa. A portion of leaves was artificially removed from a set of short shoots with both high and low gall density to cause local stress conditions. Nontreated high and low gall density short shoots were used as controls. The results show that the relative growth of leaf area measured for short shoots is negatively affected by high gall density. Artificial leaf removal, on the other hand, had positive effects on leaf area growth. Interestingly, the growth of leaf area did not differ for high gall density short shoots with leaf removal and noninfested short shoots with no leaf removal. This result may be caused by the combined, opposite effects of leaf removal and gall infestation.