Correlation of open cell-attached and excised patch clamp techniques

The excised patch clamp configuration provides a unique technique for some types of single channel analyses, but maintenance of stable, long-lasting preparations may be confounded by rundown and/or rapid loss of seal. Studies were performed on the amiloride-sensitive Na⁺ channel, located on the apical surface of A₆ cells, to determine whether the nystatininduced open cell-attached patch could serve as an alternative configuration.Compared to excised inside-out patches, stable preparations were achieved more readily with the open cell-attached patch (9% vs. 56% of attempts). In both preparations, the current voltage (I-V) relation was linear, current amplitudes were equal at opposite equivalent clamped voltages, and E _rev was zero in symmetrical Na⁺ solutions, indicating similar Na⁺ activities on the cytosolic and external surfaces of the patch. Moreover, there was no evidence that nystatin altered channel activity in the patch because slope conductance (3–4pS) and E _rev (75 mV), when the bath was perfused with a high K:low Na solution (E _Na=80 mV), were nearly equal in both patch configurations.Our results therefore indicate that the nystatininduced open cell-attached patch can serve as an alternative approach to the excised inside-out patch when experiments require modulation of univalent ions in the cytosol.We thank Dr. Olaf S. Andersen for his suggestions in the development of the open cell-attached recording technique. This work was supported by a National Institutes of Health grant (DK-18061)     

Can We Accurately Characterize Wildlife Resource Use When Telemetry Data Are Imprecise?

ABSTRACT Telemetry data have been widely used to quantify wildlife habitat relationships despite the fact that these data are inherently imprecise. All telemetry data have positional error, and failure to account for that error can lead to incorrect predictions of wildlife resource use. Several techniques have been used to account for positional error in wildlife studies. These techniques have been described in the literature, but their ability to accurately characterize wildlife resource use has never been tested. We evaluated the performance of techniques commonly used for incorporating telemetry error into studies of wildlife resource use. Our evaluation was based on imprecise telemetry data (mean telemetry error = 174 m, SD = 130 m) typical of field-based studies. We tested 5 techniques in 10 virtual environments and in one real-world environment for categorical (i.e., habitat types) and continuous (i.e., distances or elevations) rasters. Technique accuracy varied by patch size for the categorical rasters, with higher accuracy as patch size increased. At the smallest patch size (1 ha), the technique that ignores error performed best on categorical data (0.31 and 0.30 accuracy for virtual and real data, respectively); however, as patch size increased the bivariate-weighted technique performed better (0.56 accuracy at patch sizes >31 ha) and achieved complete accuracy (i.e., 1.00 accuracy) at smaller patch sizes (472 ha and 1,522 ha for virtual and real data, respectively) than any other technique. We quantified the accuracy of the continuous covariates using the mean absolute difference (MAD) in covariate value between true and estimated locations. We found that average MAD varied between 104 m (ignore telemetry error) and 140 m (rescale the covariate data) for our continuous covariate surfaces across virtual and real data sets. Techniques that rescale continuous covariate data or use a zonal mean on values within a telemetry error polygon were significantly less accurate than other techniques. Although the technique that ignored telemetry error performed best on categorical rasters with smaller average patch sizes (i.e., ≤31 ha) and on continuous rasters in our study, accuracy was so low that the utility of using point-based approaches for quantifying resource use is questionable when telemetry data are imprecise, particularly for small-patch habitat relationships.     

Time-courses of size-fractionated phosphate uptake: are larger cells better competitors for pulses of phosphate than smaller cells?

Summary Time-course experiments of phosphate uptake by size-fractionated phytoplankton were conducted in oligotrophic Kennedy and Sproat Lakes. The objective was to determine if large phytoplankton obtained more phosphate than smaller cells, when the nutrient was present at higher concentrations. Studies at Kennedy Lake revealed that uptake rates in the 0.2–3.0 m fraction were very sensitive to the time they were exposed to elevated concentrations; rates determined over the 60–120 min interval were less than 30% of those recorded over the 0–60 min interval. In contrast, there was little difference in uptake rates over these intervals for cells>3.0 m. At Sproat Lake phosphate incorporation into the two size fractions was followed after the aerial fertilization of the lake with inorganic nutrients. Following nutrient addition the proportion of phosphate entering the>3.0 m size fraction increased from ca. 35% to ca. 85%. Despite these observations, it is doubtful that larger cells are able to sequester enough phosphate from pulses to realize the same specific growth rates as their smaller counterparts.     

Non-morphogenic metabolism during shoot induction in radiata pine cotyledon explants

Summary The effects of excision, light and cytokinin (N⁶-benzyladenine) on¹⁴C-acetate metabolism in cotyledons ofPinus radiata (D. Don) were determined.¹⁴CO₂ was released and the distribution of radioactivity into lipids, sugars, organic acids and amino acids was determined. While light and cytokinin generally caused some increase in metabolism, the effect of excision, i.e., wounding, was most pronounced. Specific metabolites examined (citrate, malate, succinate, alanine, aspartate, glutamate and glutamine) were at least 50% greater in¹⁴C-labeling in excised cotyledons as compared to intact seedlings. This enhancement of wound metabolism would mask possible morphogenically-related changes occurring at that time. This research was supported by the Natural Sciences and Engineering Research Council of Canada Grant A-6467 to T.A. Thorpe.     

Discovery of isolated patches ofIcerya purchasi byRodolia cardinalis: A field study

The discovery of isolated patches of prey by the natural enemies of the cottony-cushion scaleIcerya purchasi Maskell was tested in the field on potted plants ofAcacia baileyana and citrus between November and February in South Australia. The survival of scales to adults in patches in the 4 fortnightly releases (cohort sets) was not significantly different between location-1 (under anAcacia tree harbouring scales and its natural enemies) and location-2 (about 500 m away from the nearest host plant of the scale). The temporal distribution of mortality in the scale cohorts was described by the Weibull model. The proportion of scales surviving at the 2 locations (on the 3^rd & 6^th fornight) was not significantly different suggesting that the total effect of all the mortality factors on the scales at the 2 locations was the same. The trends in prey patches destroyed in time could be explained from the period of activity of the natural enemies in the field.Rodolia cardinalis (Mulsant) had discovered the prey patches within a fortnight of the release of scale crawlers. The results substantiate earlier reports thatRodolia can find and destroy isolated scale colonies.      

Topography of the enteric nervous system in Peyer's patches of the porcine small intestine

The mechanisms of intercommunication between the immune and nervous systems are not fully understood. In the case of the intestine, the enteric nervous system is involved in the regulation of immune responses. It was therefore decided to employ immunohistochemical techniques to investigate the structural organization of the enteric nervous system in Peyer's patches of the porcine small intestine. Using antibodies against various nervous system-specific markers (protein gene product 9.5, neuron-specific enolase, neurofilament 200, S-100 protein and the glial fibrillary acidic protein), an intimate and specific structural association could be demonstrated between enteric nerves and the compartments of Peyer's patches: follicles, interfollicular regions and domes. Peyer's patches have a close topographical relationship to the two submucosal plexuses. Enteric nerves are located around the follicle in the interfollicular area — the so-called traffic area-and in the dome area, which plays an important role in the uptake and presentation of antigens.     

Identification of M cells and their distribution in rabbit intestinal Peyer's patches and appendix

The distribution of intestinal membranous (M) cells has been studied within the follicle-associated epithelium of rabbit Peyer's patches and appendix. Vimentin expression has been assessed as a primary criterion to identify rabbit M cells in tissue sections and in whole tissue preparations. This criterion has been compared to the use of the absence of alkaline phosphatase which, due to its heterogeneous distribution within the enterocyte population, is less reliable than vimentin expression as a marker for rabbit M cells. The pattern of vimentin immunostaining revealed that the majority of M cells are located in the periphery of the follicle-associated epithelium, the dome apex being largely free of M cells. This distribution was confirmed by scanning electron microscopy. Vimentin is also expressed by follicle-associated epithelial cells in the vicinity of crypts which lack the typical lymphocyte-containing pocket of M cells. Cytoplasmic peanut agglutinin binding coincides with vimentin-expression throughout the follicle-associated epithelium but is absent from vimentin-negative enterocytes. The co-localisation of these two phenotypic markers in both M cells and epithelial cells adjacent to crypts, which lack the typical morphology of fully developed rabbit M cells, suggests that they correspond to immature M cells which by their location appear to derive directly from undifferentiated crypt stem cells and not from mature columnar enterocytes.     

Aggregation and the maintenance of genetic diversity: An individual-based cellular model

Summary A cellular model, where each individual is explicitly defined, is used to describe a population of a mycophagous species ofDrosophila. Patches represent single fungal fruiting bodies which are only available as oviposition sites for a single fly generation. Standard competition equations are used to describe the interaction between larval genotypes at each patch. Dispersal of adults is obligatory and uses a simple model of patch choice to produce aggregated arrivals of adults at fresh patches. The degree to which aggregation of adults and eggs can promote coexistence of genotypes in a one-locus, two-allele system with dominance is explored. When both phenotypes (A- andaa) are aggregated, a polymorphism can be maintained for over 1000 generations even when the selective disadvantage of one phenotype (aa) is great. This model enhances the degree of polymorphism in a population, using aggregation. It does not preclude the operation of other methods which enhance the coexistence of genotypes. Therefore, it is acting to augment the degree of polymorphism maintained in species which exploit patchy and ephemeral habitats, including allDrosophila and a wide range of other organisms.     

Response of excised embryos of rice (Oryza sativa L.) to X-rays

Summary The response of rice (Oryza sativa L.) embryos to X-rays (M₁ to M₃) was studied. By means of irradiating excised embryos, both chlorophyll and macromutation were successfully induced in three genotypes of rice. However, differential responses in terms of mutation frequency, mutation spectrum and optimal levels of X-rays required for induction of mutation (chlorophyll as well as morphological) were found to exist between cultivars. In Satika and Ashkhata, LD₅₀ values and maximum induced seed sterility are concomitant to optimum level of radiation required for triggering chlorophyll mutation. However, optimum dose for induction of macromutation in Satika and Kerangserang is independent of either LD₅₀ and/or induced seed sterility.Chances of obtaining both dominant and locus specific recessive mutations in the immediate X-ray treated generation (M₁) are large. This indicates the very high degree of effectiveness of the excised embryo irradiation technique with rice.     

How landscape scale changes affect ecological processes in conservation areas: external factors influence land use by zebra (Equus burchelli) in the Okavango Delta

Most large‐bodied wildlife populations in sub‐Saharan Africa only survive in conservation areas, but are continuing to decline because external changes influence ecological processes within reserves, leading to a lack of functionality. However, failure to understand how landscape scale changes influence ecological processes limits our ability to manage protected areas. We used GPS movement data to calculate dry season home ranges for 14 zebra mares in the Okavango Delta and investigated the effects of a range of landscape characteristics (number of habitat patches, mean patch shape, mean index of juxtaposition, and interspersion) on home range size. Resource utilization functions (RUF) were calculated to investigate how specific landscape characteristics affected space use. Space use by all zebra was clustered. In the wetter (Central) parts of the Delta home range size was negatively correlated with the density of habitat patches, more complex patch shapes, low juxtaposition of habitats and an increased availability of floodplain and grassland habitats. In the drier (Peripheral) parts of the Delta, higher use by zebra was also associated with a greater availability of floodplain and grassland habitats, but a lower density of patches and simpler patch shapes. The most important landscape characteristic was not consistent between zebra within the same area of the Delta, suggesting that no single foraging strategy is substantially superior to others, and so animals using different foraging strategies may all thrive. The distribution and complexity of habitat patches are crucial in determining space use by zebra. The extent and duration of seasonal flooding is the principal process affecting habitat patch characteristics in the Okavango Delta, particularly the availability of floodplains, which are the habitat at greatest risk from climate change and anthropogenic disturbance to the Okavango's catchment basin. Understanding how the factors that determine habitat complexity may change in the future is critical to the conservation of large mammal populations. Our study shows the importance of maintaining flood levels in the Okavango Delta and how the loss of seasonal floodplains will be compounded by changes in habitat configuration, forcing zebra to change their relative space use and enlarge home ranges, leading to increased competition for key resources and population declines.